JPH11212517A - Multi-gradational image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the disorder of gradations of a half-tone display by determining an encoding method according to a combination of the movement of an observer's gaze on a display screen or an approximate value of the movement, the degree of image signal level variation of an input image signal on the screen, and the degree of image signal level variation in its temporal direction. SOLUTION: When an input image is displayed by supplying a gaze detecting circuit 2 with an input image signal 1 as, for example, a digital signal representing the value of a video signal with 8 bits, the movement of the observer who does tracing on the screen is detected. At the same time, an image level variation detecting circuit 3 detects an image variation pattern on the screen and detects whether the variation degree is large or small. A combination deciding circuit 4 determines the operation of a selecting circuit 5 according to a combination of the outputs of the gaze detecting circuit 2 and image level variation detecting circuit 3. Namely, an encoding method of a subfield encoding means is determined according to a combination of the signal level variation degree of the input image signal 1 on the screen and the signal level variation degree in its temporal direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device for displaying a multi-gradation display by dividing one field of an image into a plurality of sub-field images and displaying the divided images. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-tone image display device capable of displaying a tone display with improved tone disturbance.

[0002]

2. Description of the Related Art When a multi-tone image is displayed using a display device based on binary display such as a plasma display, one field of the image is divided into a plurality of subfields, and each subfield is divided into a plurality of subfields. There is known a method of displaying an image by giving a predetermined luminance weight and controlling the presence or absence of light emission for each subfield. For example, in order to display 256 gradations, one field of the input signal is divided into eight subfields, and the luminance weight of each subfield is set to “1”, “2”, “4”, “8”, "16",
"32", "64", and "128". Assuming that the input signal is an 8-bit digital signal, this is assigned to eight sub-field images in order from the least significant bit and displayed. Each subfield image is a binary image.

[0003]

However, in such a conventional method of displaying 256 gradations using eight subfields, a so-called pseudo-contour-like gradation disturbance may occur in moving image display. Are known.

[0004] The generation of a pseudo contour when displaying a moving image will be described with reference to FIGS. 15 and 16. FIG. 15 shows a case where an image having two adjacent patterns of level “15” and level “16” (an example of which is shown in FIG. 16) is displayed, and when the adjacent pattern follows a pattern that has been translated. This shows what is being observed. In a display device that divides one field of an input image into a plurality of subfields and performs gradation display, when a still image is displayed,
The average luminance of one field of the observed image is A in FIG.
It is expressed by the integral of the light emission between -A ', and the gradation is correctly displayed.

On the other hand, when a moving image is displayed, on the retina, between BB ′ in FIG.
The emission integral during C 'is observed. Between BB ', the combined value of each bit is almost 0, and the sum of each bit between CC' is almost "31". As described above, when a portion where two levels “15” and “16” are adjacent to each other is observed, in the level change portion, the observed luminance level is significantly disturbed by the motion of the image as shown in FIG. Although FIG. 15 illustrates that light emission is continuously performed with a predetermined width for each subfield, in an actual plasma display, each subfield has the number of times corresponding to each luminance weight. Although it is composed of a set of pulsed light emission, the gradation disturbance at the time of displaying a moving image is essentially the same.

FIG. 15 shows only 5 subfields out of 8 subfields for simplicity. As described above, since an attempt is made to express a halftone by integrating the luminance of each subfield in the time direction, if the line of sight moves in a moving image, the image at a position different from the original pixel position over time elapses. Since the weight of each bit is integrated, there is a problem that the halftone display is greatly disturbed.

Since this halftone disturbance is recognized so that a false contour appears in the image, it is hereinafter referred to as a moving image pseudo contour.

Further, the movement of the line of sight on the display screen of the observer when a moving image is displayed on a normal image display device has a strong correlation with the movement of the image on the display image device. And the movement of the image is not particularly distinguished.

[0009]

In order to solve the above-mentioned problems, a multi-tone image display device according to the present invention comprises:
A subfield encoding unit that divides a field into a plurality of subfields, and encodes the luminance of each subfield in an on or off state for each of the subfields; An image display device for controlling and displaying an image, wherein the movement of a line of sight or an approximate value of the movement of a line of sight on a display screen of an observer when a moving image is displayed on the image display device, An encoding method in the sub-field encoding means is determined based on a combination of a signal level variation in a screen and a signal level variation in the time direction of the input image signal.

[0010] Further, the approximate value of the amount of movement of the line of sight is a value approximated by a change value in the time direction of each pixel of the input image signal.

Further, the approximate value of the amount of movement of the line of sight is a value approximated by a motion vector value of a plurality of pixels detected from the input image signal.

Further, the approximate value of the amount of movement of the line of sight is a value obtained by correcting a change value in the time direction of each pixel of the input image signal with an edge component of the input signal.

The approximate value of the amount of movement of the line of sight is corrected by a value obtained by correcting a change value of the input image signal in the time direction for each pixel by a correction value determined by a coding method in the subfield coding means. It is characterized by having done.

Further, when the correction value determined by the encoding method in the subfield encoding means continuously changes the input image signal in accordance with the encoding method, the correction value determined by the temporal change of the luminance value to be displayed. It is characterized by the degree of discontinuity.

Further, the degree of change in the signal level of the input image signal within the screen is a gradient of the signal level of the input image signal.

Further, the gradient of the signal level of the input image signal is calculated from the horizontal or vertical gradient of the input image signal, or the horizontal and vertical gradients of the input image signal. It is characterized in that the inclination is adjusted.

Further, the degree of change in the signal level of the input image signal within the screen is obtained by correcting the inclination of the signal level of the input image signal by a correction value determined by an encoding method in the subfield encoding means. Value.

Further, when the correction value determined by the encoding method in the subfield encoding means changes the input image signal continuously according to the encoding method, the temporal value of the displayed luminance value is changed. It is characterized by the degree of discontinuity.

Further, the degree of change in the signal level of the input image signal in the screen is a value calculated from a representative value, a maximum value and a minimum value of the image signal level in a predetermined area of the input image signal. And

The degree of change in the image signal level of the input image signal within the screen is determined by detecting a flat area of the image from the image including the pixel of interest in the input image signal, and defining a shape isolated from the detected flat area. And a value calculated from the representative value, the maximum value, and the minimum value of the image signal level of the region from which the pixel region has been removed.

Further, the degree of change in the signal level of the input image signal within the screen is an edge component of the input image signal.

Further, the degree of change in the signal level in the time direction of the input image signal is a value obtained by arithmetically operating images of two or more fields separated by a predetermined short field period.

The signal level change degree of the input image signal in the time direction is obtained by performing arithmetic operation on images of two or more fields separated by a predetermined short field period. It is a value corrected by the component.

Further, the encoding method in the subfield encoding means may use a large luminance weight in a portion where the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is small. It is characterized in that gradation control is performed with priority given to a combination that suppresses on-control of a subfield as much as possible.

Further, the encoding method in the sub-field encoding means may be arranged such that, in a portion where the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is detected largely, The present invention is characterized in that the coding method is limited to coding in which the level increase of the input image signal and the distribution of the light emission pattern have a strong monotonically increasing correlation.

In the encoding method in the sub-field encoding means, in a portion where the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is detected largely, The coding is limited to coding in which the level increase of the input image signal and the distribution of the light emission pattern have a strong monotonically increasing correlation, and the coding is performed so that an error between the input image signal and the display luminance is almost canceled in adjacent pixels. The method is characterized in that the conversion method is controlled.

If the encoding method in the sub-field encoding means is such that the change in the signal level of the region of interest is small among the changes in the image signal level of the input image signal in the screen, The encoding is characterized in that the switching of the on-control or the off-control of the subfield having the largest luminance weight is suppressed as much as possible in the focused area.

When the degree of change in the image signal level of the region of interest is small among the degrees of change in the image signal level of the input image signal, the image signal of the input image signal is focused on. Of the image signal levels of the region, using a signal subjected to amplitude limitation limited to a range including a large number, the encoding method in the subfield encoding means in the region of interest sets the largest luminance weight The encoding is characterized in that the switching of the on-control or the off-control of the subfield is suppressed as much as possible.

The encoding method in the sub-field encoding means may include a step of detecting a large amount of movement of the line of sight of the observer with respect to the display screen of the image display device or an approximate value of the amount of movement of the line of sight. A portion where the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is detected to be small, and a region of interest of the signal level change degree within the screen of the input image signal And a portion where the degree of change of the signal level is small.

The encoding method in the sub-field encoding means may include a step of detecting a large amount of movement of an observer's line of sight or an approximate value of the amount of movement of the line of sight with respect to a display screen of the image display device; A portion where the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is detected to be small, and a region of interest of the signal level change degree within the screen of the input image signal Are changed by a portion where the degree of change of the signal level is small and a boundary between these portions.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention (claim 1) divides one field of an input image signal into a plurality of subfields,
An image display device comprising the subfield encoding means for encoding the luminance of each subfield to an on or off state for each of the subfields, and performing gradation control by the subfield encoding means to display an image Wherein an encoding method in the subfield encoding means is determined based on a combination of a degree of change in the signal level of the input image signal in a screen and a degree of change in the signal level of the input image signal in a time direction. It is characterized by the following.

For this purpose, a subfield encoding method which prioritizes the elimination of the pseudo-contour of the moving image is used in the image portion where the pseudo-contour of the moving image is likely to occur due to the combination of the specific image pattern and the motion of the specific image. By using a subfield encoding method that prioritizes gradation display characteristics in an image portion in which a moving image pseudo contour does not occur due to image motion, it is possible to realize good image display over both a still image and a moving image display. .

In the multi-tone image display device according to the present invention (claim 2), the approximate value of the amount of movement of the line of sight is a value approximated by a change in the time direction of each pixel of the input image signal. Because of this feature, it is possible to provide a means for easily detecting a value approximating the movement of the line of sight that follows when the observer observes the moving image displayed on the image.

Further, in the multi-tone image display device of the present invention (claim 3), the approximate value of the amount of movement of the line of sight is a value approximated by a motion vector value of a plurality of pixels detected from the input image signal. Because of the feature, it is possible to change the sub-field encoding method by approximating the movement of the line of sight that follows when the observer observes the moving image displayed in the image, the still image and the moving image display Good image display can be realized in both cases.

In the multi-tone image display device according to the present invention (claim 4), the approximate value of the amount of movement of the line of sight is a change in the time direction of the input image signal for each pixel, and the edge component of the input signal. Since the feature is to use the value corrected in the above, it is possible to prevent a slight movement of the image at the edge portion of the image from being converted into a large temporal change,
The motion amount can be correctly approximated without excessively evaluating the motion amount at the edge portion of the image.

In the multi-tone image display device according to the present invention (claim 5), the approximate value of the amount of movement of the line of sight is obtained by converting the temporal change value of each pixel of the input image signal into the subfield encoding means. Is characterized by using a value corrected by the correction value determined by the encoding method in the above, so that the encoding method evaluates the motion detection sensitivity particularly high in a signal level portion where a moving image false contour is likely to be noticeably generated. Therefore, it is possible to provide a means for appropriately detecting a motion, preventing a false contour of a moving image from occurring, and realizing a high-quality image display.

Further, the correction value determined by the encoding method in the sub-field encoding means in the multi-tone image display device of the present invention (claim 6) can be obtained by continuously converting the input image signal according to the encoding method. If you change it,
Characterized by the degree of temporal discontinuity of the displayed luminance value, the encoding method can be used to evaluate the motion detection sensitivity particularly at the signal level where video false contours are likely to occur significantly. In addition, it is possible to provide a means for appropriately detecting a motion, eliminating a gradation display disturbance at the time of displaying a moving image, and realizing a high-quality image display.

Further, the multi-tone image display device according to the present invention (claim 7) is characterized in that the gradient of the signal level of the input image signal is used as the degree of change in the signal level of the input image signal within the screen. I have. Since the gradient of the signal level of the input image signal can be relatively easily detected by a linear operation of a plurality of pixels, and in many cases, there is a correlation between the gradient of the signal level and the degree of the false contour of a moving image, It is possible to provide a means for effectively grasping an image pattern and an image motion in which pseudo contours are likely to occur, effectively eliminating moving image pseudo contours, and realizing high-quality image display.

Further, in the multi-tone image display device according to the present invention (claim 8), the gradient of the signal level of the input image signal is
Horizontal or vertical gradient of the input image signal,
Alternatively, a gradient calculated from the horizontal gradient and the vertical gradient of the input image signal is used. The calculation of the inclination of the image only in the horizontal direction and the inclination of only the vertical direction can be relatively easily calculated, and the inclination of the two-dimensional image can be easily calculated by using the square root of the two. be able to. In many cases, there is a correlation between the signal level gradient and the degree of the pseudo contour of the moving image. Therefore, this configuration makes it easy to effectively and effectively grasp the image pattern and the motion of the image in which the pseudo contour of the moving image is likely to occur. It is possible to provide a means for effectively eliminating the contour and realizing high-quality image display.

Further, the multi-tone image display device of the present invention (claim 9) corrects the gradient of the signal level of the input image signal by the correction value determined by the encoding method in the subfield encoding means. Since the corrected value is used as the degree of change in the signal level of the input image signal within the screen, it is possible to select and detect an image portion in which a moving image pseudo contour is likely to be noticeably generated. It is possible to provide a means for effectively eliminating the contour and realizing high-quality image display.

Further, in the multi-tone image display device of the present invention (claim 10), the correction value determined by the encoding method in the subfield encoding means is used to continuously convert the input image signal according to the encoding method. Is changed to the degree of temporal discontinuity of the displayed luminance value. At the point where the light emission pattern becomes discontinuous in time, moving image false contours are likely to occur.Therefore, considering the luminance discontinuity at the time of moving image display, which tends to occur according to the subfield encoding method, select A field coding method can be determined.

Further, in the multi-tone image display device according to the present invention (claim 11), the degree of change in the signal level of the input image signal within the screen is determined in a pixel area temporally or spatially close to the pixel of interest. , The representative value, the maximum value, and the minimum value of the image signal level in this area are detected. For this reason, the distribution range of the image signal is limited within a region centered on the pixel of interest, and a subfield encoding method that minimizes the generation of moving image false contours in this distribution range is selected and adopted. Becomes possible.

In the multi-tone image display device according to the present invention (claim 12), a representative value of an image signal level in a flat pixel area including a pixel of interest, The maximum and minimum values are detected. For this reason, a region centered on the pixel of interest is a flat portion of the image, and the distribution range of the image signal is limited. Can be adopted. Note that it is empirically known that a flat portion of an image is relatively conspicuous even though the absolute amount of a generated pseudo contour of a moving image is small, and a flat portion of an image has a small spatial variation of an image signal level. In some cases, it is difficult to approximate the amount of movement of the line of sight using only the temporal difference between images, and so on. It is possible to reduce disturbance.

Further, according to the multi-tone image display device of the present invention (claim 13), the degree of change in the image signal level of the input image signal within the screen is determined based on the image including the pixel of interest in the input image signal. Detecting a region, and calculating a value calculated from a representative value and a maximum value and a minimum value of an image signal level of the region in which a pixel region having an isolated shape is removed from the detected flat region. Therefore, it is possible to stabilize the switching of the encoding method in the above, and to improve the effect of reducing the false contour of the moving image in the flat portion of the image.

Further, the multi-tone image display device of the present invention (claim 14) is characterized in that an edge component of the input image signal is used as the degree of change in the signal level of the input image signal within the screen. For this reason, it is possible to determine a subfield encoding method by specifically detecting a case where there is a sharp edge component and the occurrence of a moving image false contour is relatively inconspicuous visually.

In the multi-tone image display device according to the present invention (claim 15), the signal level change degree of the input image signal in the time direction is a value obtained by arithmetically operating an image of a predetermined plurality of fields. It is characterized by: With this value, the movement of the line of sight can be relatively easily approximated, and the subfield encoding method can be determined according to the movement of the image.

In the multi-tone image display device according to the present invention (claim 16), the value obtained by arithmetically operating images of a plurality of fields is used as the time-dependent signal level change degree of the input image signal. It is characterized in that it is a value corrected by the edge component of the input image signal. For this reason, when using the difference between a plurality of images as the amount of motion, it is possible to prevent the amount of motion from being overestimated at the edge portion of the image, to cause only slight image motion, and to reduce the pseudo contour of the moving image. If this has not happened, the subfield encoding method can be appropriately selected.

Further, in the multi-tone image display device according to the present invention (claim 17), in a portion where the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is small, It is characterized in that gradation control is performed with priority given to a combination that suppresses ON control of a subfield having a large luminance weight as much as possible.

The applicant's earlier application “Japanese Patent Application No. 9-162258”
As shown in the figure, among the combinations of on / off of the subfields capable of expressing the predetermined luminance, the encoding that suppresses the ON control of the subfield having the large luminance weight as much as possible is the worst case of generating the pseudo contour of the moving image as a whole. Since the value is suppressed, even in a region where the motion of the image cannot be accurately detected for some reason, it is possible to minimize the generation of the false contour of the moving image.

Further, the encoding method in the subfield encoding means in the multi-tone image display device of the present invention (claim 18) is characterized in that the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the amount of movement of the line of sight. In a portion where the approximate value of the motion amount is detected to be large, the encoding method is limited to an encoding method in which the level increase of the input image signal and the distribution of the light emission pattern have a strong monotonically increasing correlation.

In encoding using only a combination in which the level increase of the input image signal and the distribution of the light emission pattern have a monotonically increasing correlation, almost no generation of moving image pseudo-contours is observed. By using the encoding, it is possible to prevent the generation of a pseudo contour of a moving image.

Further, the encoding method in the subfield encoding means in the multi-tone image display device of the present invention (claim 19) is characterized in that the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the amount of movement of the line of sight. In the part where the approximate value of the motion amount is detected to be large, the coding is limited to coding having a strong correlation between the level increase of the input image signal and the light emission pattern distribution, and the input image signal and the display luminance The encoding method is characterized in that the encoding method is controlled such that the error of (1) is almost canceled in the adjacent pixels.

For this reason, when an image is displayed only on a code that hardly generates a pseudo contour of a moving image, the limitation of the number of displayable gradations is compensated for. As a result, a sufficient number of gradations for practical use can be ensured, and good image display can be performed.

Further, the multi-tone image display device according to the present invention (claim 20) provides a multi-gradation image display device in which, when the degree of change of the image signal level of the area of interest is small among the degree of change of the image signal level of the input image signal. Uses, as an image signal of the input image signal, a signal subjected to an amplitude limitation that limits an image signal level of a region of interest to a range including a large number of the image signal levels, and performs the processing in the region of interest. The encoding method in the sub-field encoding means is characterized in that encoding is performed with the switching of the on-control or the off-control of the sub-field having the largest luminance weight suppressed as much as possible.

For this reason, it is possible to shape the shape of the region detected as the image flat portion and encode the image signal in this region, suppress unnecessary switching of the encoding method, and perceive the noise as noise. The generation of false contours of moving images can be suppressed.

Further, according to the encoding method of the subfield encoding means in the multi-tone image display device of the present invention (claim 21), the region of interest in the degree of signal level change in the screen of the input image signal is When the degree of change of the signal level of the subfield is small, the coding is performed in such a manner that switching between ON control and OFF control of the subfield having the largest luminance weight is suppressed as much as possible in the region of interest. . For this reason, it is possible to suppress the on / off switching control of the subfield having a large luminance weight, which is a main cause of the generation of the moving image pseudo contour, and to suppress the occurrence of the moving image pseudo contour in the area.

Further, the encoding method in the subfield encoding means in the multi-tone image display device according to the present invention (claims 22 and 23) is characterized in that the amount of movement of the observer's line of sight with respect to the display screen of the image display device or the line of sight A portion where the approximate value of the amount of movement of the observer is detected to be large, a portion where the amount of movement of the observer's line of sight to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is detected to be small, and the input image signal In this case, the change is made in accordance with the portion of the signal level change degree in the area of interest out of the signal level change degree in the screen.

For this purpose, the amount of movement of the observer's line of sight and the level of change of the input image signal level are not determined and encoded independently, but the amount of movement of the observer's line of sight and the input image signal level are not determined. It is possible to determine an encoding method that organically combines the degree of change and the like. In other words, the first encoding method and the amount of movement of the observer's line of sight are unknown in a portion where the amount of movement of the line of sight of the observer is detected and the degree of change of the input image signal level is large, but the amount of movement of the line of sight of the observer is unknown. In the part where the degree of change is small, the second encoding method is selected, and in the part where the amount of movement of the observer's line of sight is detected to be small, the third encoding method is selected. It is possible to use an optimal subfield encoding method based on a combination of the degree of change in the input image signal level.

Further, in the encoding method of the subfield encoding means in the multi-tone image display device of the present invention (claims 24 and 25), the switching of the encoding method is conspicuous at the boundary where the encoding method is changed. It is characterized by selecting an encoding method so as not to cause a wide range of good image display in a still image and a moving image.

(Embodiment 1) Hereinafter, Embodiment 1 of the present invention (claims 1, 18, 19, and 22) will be described with reference to the drawings. FIG. 1 is a configuration diagram of a plasma display that is a multi-tone image display device according to the first embodiment.

In FIG. 1, reference numeral 1 denotes an input image signal, and reference numeral 2 denotes a line-of-sight movement detecting circuit for detecting the movement of the line of sight of an observer with respect to the input image signal. Reference numeral 3 denotes an image level change detection circuit for detecting a spatial change of the image level with respect to the input image signal.
Is a combination judging circuit for judging a combination of the output states of the above-mentioned eye movement detecting circuit 2 and image level change detecting circuit 3; 5 is a moving picture coding circuit for coding a moving picture portion of an input image; Is a still image encoding circuit for encoding a still image portion of an input image, 8 is a selection circuit,
Reference numeral 9 denotes a subfield control circuit for converting a signal representing a luminance level into a subfield pattern which is a binary signal.

The input image signal 1 is, for example, a digital signal expressing the value of a video signal in 8 bits. The input image signal 1 is supplied to a line-of-sight detection circuit 2 to detect a movement that the observer would follow on the screen when the input image is displayed. At the same time, the image level change detection circuit 3 detects an image change pattern in the screen and detects the magnitude of the change. The combination determination circuit 4 determines the operation of the selection circuit 5 based on the combination of the output states of the visual line detection circuit 2 and the image level change detection circuit 3. FIG. 2 shows an example of the determination operation in the combination determination circuit 4.

As can be seen from FIG.
Determines the operation of the selection circuit 5 based on the movement of the line of sight and the degree of change in the image level. That is, when the fluctuation of the image level in the screen is large and the movement of the line of sight is large, the selection circuit 5 selects 5a.

On the other hand, when the movement of the line of sight is small or when the degree of change of the image level in the screen is small, the selection circuit 5
Selects 5b. A moving image encoding circuit 6 for encoding the input image signal 1 using an encoding method suitable for a moving image is connected to 5a, and an encoding method suitable for a still image is used for the input image signal 1 for 5b. Image encoding circuit 7 for encoding
Is connected. The signal 5c selected by the selection circuit 5 is converted by the subfield circuit 9 into a binary subfield pattern signal, and the plasma display 1
0 is supplied. The plasma display 10 emits pulse light in the number of times proportional to 5c, and realizes a gray scale display.

In the first embodiment of the present invention, the number of subfields is eight and the number of display gradations is 256 for simplicity. The luminance weight and the order of each subfield are the same as in the conventional example, ie, “1”, “2”, “4”,
They are "8", "16", "32", "64", and "128".

In general, when the fluctuation of the image level in the screen is large and the movement of the line of sight is large, the pseudo contour of the moving image is likely to be generated. Conversely, when there is no movement of the line of sight or when there is no change in the level of the image in the screen. Does not generate a moving image pseudo-contour, and thus attempts to control an encoding method when an image signal is converted into a subfield pattern according to the state of an image or the movement of a line of sight.

Note that, in principle, a pseudo-contour of a moving image does not occur in a still image portion. However, since the subject is stationary, an observer often watches the image depending on the image content, and a sufficient gradation display characteristic is required. You. For example, in the case of a single color, it is often the case that at least 256-color gradation expression is necessary.

Although it is often not necessary to accurately reproduce an image in an individual pixel unit in a portion having a strong movement, it is often the case that the entire subject makes a meaningful movement, and the line of sight follows the movement. It is necessary to suppress so-called moving image false contours as much as possible.

By adopting the configuration as shown in FIG. 1, it is possible to perform encoding while securing the gradation display characteristics of 256 colors in a still image portion, and perform encoding with priority on suppression of a pseudo contour of a moving image in a moving image portion. As a result, good image display can be performed for both still images and moving images.

Hereinafter, the configuration and operation of the moving picture coding circuit 6 will be described. The moving picture coding circuit 6 can be configured as shown in FIG. 3, for example. In FIG.
Is an addition circuit, and 602 is a display signal encoding circuit, the operation of which is defined by the input / output characteristics shown in FIG. 603 is a display error detection circuit, 604 to 607 are delay circuits, and 608 to 6
11 is a coefficient circuit. The image signal of the moving image portion is encoded by the display signal encoding circuit 602 via the addition circuit 601. The input of the display signal encoding circuit 602 changes from “0” to “2”.
55 ", while the display signal encoding circuit 60
As can be seen from FIG. 4, the output of No. 2 is an output limited to nine types.

That is, when the input level is “1”, only the first subfield of the luminance weight “1” is turned “ON”. When the input level is “2”, the first subfield of the luminance weight “1” is also turned on. Only the field is controlled to be “on”. Similarly, for example, when the input level is “6” to “11”
In the case of, the output of the display signal encoding circuit 602 includes the first sub-field of the luminance weight “1”, the second sub-field of the luminance weight “2”, and the third sub-field of the luminance weight “4”. The state is controlled to be “ON”.
That is, even if the input level changes from "6" to "11", the output of the display signal encoding circuit 602 is limited to a constant value and output.

As described above, for the input levels “0” to “255” of the display signal encoding circuit 602, the output of the display signal encoding circuit 602 is limited to nine types of signals. When these nine signals are converted into a subfield pattern by the subfield circuit 9 and supplied to the plasma display 10 to emit light, the increase in the input level and the distribution of the light emission pattern have a monotonically increasing correlation. As a result, almost no generation of moving image false contours is observed.

However, when the encoded output is displayed as it is, “0”, “1”, “3”, “7”, “1”
Only 9 gradations of 5 "," 31 "," 63 "," 127 ", and" 255 "are displayed, and the original 256 gradations cannot be displayed, and a display error occurs depending on the input level.

The display error detection circuit 603 detects the difference between the output of the addition circuit 601 and the output of the display signal encoding circuit 602, and supplies the difference to the coefficient circuits 608 to 611 via the delay circuits 604 to 607. Then, they are supplied to the adders 601 to form loops. This loop is known as the “error diffusion method”, and diffuses the display error generated at the pixel, that is, the error between the addition circuit 601 and the display signal encoding circuit 602, to four surrounding pixels, thereby obtaining the original loop. It is intended to approximately realize a gradation display. In the case of this example, the four peripheral pixels are the right, lower right, lower, and lower left pixels of the pixel, and the above-described display errors are distributed to these pixels at a ratio of 7: 1: 5: 3, respectively.

This method is different from the so-called “tissue dither method”, in which fixed pattern disturbance and unnecessary reduction in resolution are small, gradation can be satisfactorily ensured, and it is often used in liquid crystal devices and the like. It is a technique that has been used. However, when this error diffusion process is used for a display device such as a plasma display which has a relatively high response speed to display a still image and observe it from a close distance, a noise-like pattern due to this error diffusion is detected. There are side effects, and it is not preferable to use the error diffusion method for all moving images and still images. However, by using the above-described limited coding and error diffusion method only for the moving image part, the noise-like pattern is not so noticeable, and the pseudo-outline of the moving image is almost completely suppressed, while the side effect of the noise-like pattern and the like is suppressed. Image display in which the occurrence of the image is suppressed.

In a moving image portion, a noise-like pattern may be observed due to error diffusion. However, in an actual operation of the plasma display, a light emission pattern is distributed over a plurality of subfields. ,
It emits light over a certain period of time, causing a spatial filter effect.In the case of a moving image, the line of sight moves following the subject, and noise due to error diffusion formed on the retina during this time Since the pattern is almost random and averaged, the level of the noise-like pattern that is practically perceived is considerably low, indicating that sufficient gradation characteristics can be secured.

Since the still image encoding circuit 7 performs the same encoding as the conventional example in accordance with the conversion rule shown in FIG. 5, it goes without saying that 256 gradations are correctly displayed.

As described above, according to the present embodiment, the movement of the line of sight of the observer who observes the image is detected, and the change in the image signal level in the screen is detected. After determining the part where the image is likely to occur, the moving image part and the still image part are encoded differently and the driving using the subfield is performed in the plasma display, so that the occurrence of the moving image pseudo contour is suppressed. In the still image portion, an image with 256 gradations can be correctly displayed. In the moving image coding, since it is fair that a display error is canceled by surrounding pixels, a sufficient number of displayable gradations can be realized even in a moving image portion.

(Embodiment 2) Hereinafter, Embodiment 2 of the present invention (claims 1, 2, 4 to 12, 15 to 19, and 22) will be described.
Will be described with reference to the drawings. The description of the same parts as in the first embodiment will be omitted, and only the parts that are essentially different from the first embodiment will be described.

The second embodiment of the present invention is intended to further suppress the generation of a moving image false contour in an image flat portion, in addition to the function of the first embodiment of the present invention. That is, in general, the moving image pseudo contour is remarkably observed when the motion of the image is large and the inclination of the image is within a certain range. Such a portion can be detected and countermeasured by the method according to the first embodiment of the present invention described above.

However, even after such measures have been taken, when the image quality is evaluated in consideration of a further improvement in image quality, gradation disturbance sometimes occurs in an image flat portion included in a moving object. It turned out to be acceptable. It has been found that this is a noise-like moving image pseudo-contour generated when the visual line follows the image flat portion, even if the signal level is slightly inclined even in the image flat portion. The second embodiment of the present invention aims at eliminating the gradation disturbance in the flat portion of the image.

FIG. 6 is a configuration diagram of a plasma display which is a multi-tone image display device according to the second embodiment of the present invention. 6, 1 is an input image signal, 21 is a frame memory, 22 is a difference detection circuit, 23 is a difference correction circuit, 24 is an edge correction circuit, 31 is a horizontal inclination detection circuit, 32 is a vertical inclination detection circuit, 33 Is an edge detection circuit, 34 is a two-dimensional inclination detection circuit, 35 is an inclination correction circuit, 36 is an image flat part detection circuit, 37 is a maximum value detection circuit, 38 is a representative value detection circuit, 39 is a minimum value detection circuit, 4
0 is a distribution determination circuit, 41 is a combination determination circuit, 51 is a selection circuit, 61 is a moving image coding circuit, 71 is a still image coding circuit, 81 is a flat part coding circuit, and 90 is an input 8-bit digital value. A subfield control circuit that converts a subfield pattern into ten subfields, wherein 100 has a luminance weight of “1” for one field,
"2", "4", "8", "16", "24", "3"
This is a plasma display that emits light while being divided into ten subfields of 2 "," 40 "," 56 ", and" 72 ".

The operation of the second embodiment configured as described above will be described below. The input image signal 1 is
After being supplied to the moving image encoding circuit 61, the still image encoding circuit 71, and the flat portion encoding circuit 81, and one of them is selected by the selection circuit 51, the same as in the first embodiment of the present invention,
The signal is converted into a binary subfield pattern signal by the subfield control circuit 90, and the plasma display 1
00 is supplied.

The plasma display 100 realizes a gray scale display by performing pulse emission in the number of times proportional to the input image signal value during one field period. The configuration of the moving picture coding circuit 61 is almost the same as that of FIG. 3 of the first embodiment of the present invention, except that the coding method of the display signal coding circuit 602 of the first embodiment is FIG. On the other hand, in the second embodiment, the portion corresponding to the display signal encoding circuit performs encoding based on the conversion rule shown in FIG. That is, as can be seen from FIG. 7, the output is “0”, “1”, “3”, “7”, “15”, “15” for 256 input signal levels “0” to “255”. 3
1 "," 55 "," 87 "," 127 "," 183 ",
It is assumed that the number is limited to 11 kinds of “255”.

In this coding method, similarly to the case of FIG. 4, the distribution of the light emission pattern monotonously spreads with the increase of the input signal level, and the correlation of the monotone increase between the input signal level and the light emission pattern is obtained. It has a strong characteristic, and therefore has a characteristic that a moving image false contour hardly occurs. That is, the 11 types of codes shown in FIG. 7 only increase the number of subfields that are turned on with an increase in the input signal level, and there are no subfields that are turned off when the input signal level is increased. It can be said that the coding is limited to the combinations that do not have such a combination, and that the temporal change of the light emission is monotonously increased with respect to the change of the input signal level. For this reason, it can be interpreted that almost no generation of a moving image false contour is observed.

On the other hand, the still image encoding circuit 71 encodes the input image signal 1 according to a conversion rule as shown in FIG. This encoding gives priority to a combination that suppresses light emission of a subfield having a large luminance weight as much as possible. Such encoding is performed by displaying 256 gradations as shown by the earlier application of the present applicant. The number of possible gradations is maintained, and the amount of generation of the moving image false contour is relatively small over the entire range of the input image level. For this reason, when the still image portion is encoded by the still image encoding circuit 61,
Sufficient gradation display characteristics can be maintained, and even if a moving image portion is erroneously processed as a still image, a generated moving image false contour can be reduced.

Next, a system for detecting the motion of an image will be described. First, a difference between one frame of an image is obtained by the frame memory 21 and the difference detection circuit 22. The detected inter-frame difference reflects the "movement of the image" to some extent, but since the level at which the moving image false contour is likely to occur differs depending on the level of the image, the difference correction circuit 23 performs correction in accordance with this level. . For this correction, for example, the coefficients shown in FIG. 9 can be used.

In FIG. 9, a portion having a large value is corrected so as to increase the motion of the image, and a reverse portion is corrected so as to reduce the motion of the image. The correction value in FIG. 9 can be determined from the encoding characteristics of the still image encoding circuit 71. When a moving image is temporarily encoded and displayed using the still image encoding circuit 71, a moving image pseudo contour occurs. The numerical value at an easy signal level is increased. The output of the difference correction circuit 23 is corrected by the edge correction circuit 24 according to the strength of the edge. That is, in the edge portion of the image, the difference output becomes large even with a slight movement of the image,
Since the movement of the image cannot be correctly reflected, by correcting the output of the difference correction circuit 23 in a portion where the edge of the image is strong, it is possible to obtain a signal closer to the movement of the line of sight. As described above, by the processing between the frame memory 21 and the edge correction circuit 24, it is possible to detect the motion of the image that is similar to the motion of the line of sight that causes the generation of the false contour of the moving image.

Next, in order to more accurately detect a portion where a false contour of a moving image is likely to occur in an image, a gradient of an image signal in a screen is detected. Horizontal inclination detection circuit 31
And the vertical gradient detection circuit 32 detects the horizontal and vertical gradients of the screen, respectively. Since these can be performed by one-dimensional calculation, it can be realized at low cost. An edge portion can be detected from the local maximum of the horizontal and vertical gradients using the edge detection circuit 33, and a two-dimensional gradient detection circuit can be detected based on the sum of squares of the horizontal and vertical gradients. 34 of image 2
The dimensional gradient can be detected.

Moving image pseudo-contours tend to occur in portions where the image has a high degree of inclination, and can be used as candidates for a moving image pseudo-contour occurrence region using the two-dimensional inclination of the image. Because the intensity of the false contour of the moving image varies not only depending on the degree but also on the level of the pixel of interest,
By correcting the inclination detected by the inclination correction circuit 35 in accordance with the level of the image signal, it is possible to more reliably detect a portion where a pseudo contour is likely to occur. In addition,
The correction in the inclination correction circuit 35 is performed by the difference correction circuit 23.
The same correction coefficients as those used in the correction shown in FIG. 9 can be used. As described above, by the processing between the horizontal inclination detection circuit 31 and the inclination correction circuit 35, it is possible to detect the degree of change in the image level and to select an area where a moving image false contour easily occurs.

The image flat part detection circuit 36 detects, from the input image signal, an area where the signal level has little change in space or an area where there is little change in space and time, as an image flat part. The maximum value, representative value,
The minimum value is detected by the maximum value detection circuit 37, the representative value detection circuit 38, and the minimum value detection circuit 39, respectively, and the distribution state of the signal level in the flat region is determined by the distribution determination circuit 40 based on these values. As a result, the region of the flat portion in the image and the distribution range of the signal in this region are determined. The output of the distribution judging circuit 40 is supplied to the flat part encoding circuit 81 to determine the operation condition.

The flat part encoding circuit 81 determines an encoding method according to the representative value and distribution state of the image signal level of the detected image flat part. For example, it is possible to select encoding such that the peak value of the pseudo contour of the moving image is equal to or less than a predetermined value within the range between the maximum value and the minimum value of the image signal level of the detected image flat portion. FIGS. 10 and 11 show examples of coding in the flat part coding circuit 81. FIG. For example, if the maximum value of the image signal level of the detected image flat portion is “18”
Assuming that “0” and the minimum value are “100”, the image flat part performs encoding according to the conversion rule based on FIG.

In this way, the image signal level becomes "9
During the period from "6" to "183", the ninth subfield having the largest luminance weight among the subfield patterns that emit light does not change at all, and the generation of a strong moving image false contour can be avoided.

In addition, assuming that the maximum value of the image signal level of the detected image flat portion is "200" and the minimum value is "95", the image flat portion is coded according to the conversion rule based on FIG.

In this way, the image signal level becomes "7
During the period from "2" to "255", no change occurs in the tenth subfield having the largest luminance weight among the subfield patterns that emit light, and generation of a strong moving image false contour can be avoided.

In the above configuration, the detected representative value is not directly used. However, when the detected maximum value and minimum value are far from the detected representative value, or when the maximum value is 255 In the case of a special pattern in which the value is close to and the minimum value is close to 0, the detected area is not regarded as a flat image area. And so on.

As described above, in the image flat portion, the encoding is performed in accordance with the signal distribution in the flat region, whereby
Since the switching of the on / off control of the subfield having the largest luminance weight is suppressed in each image flat portion, the generation of the moving image false contour can be further reduced. Since the original image is flat and uniform in the flat part of the image, it may be relatively conspicuous when moving image false contours and noise occur, and suppressing this noise-like moving image false contour is effective in improving image quality. Is big.

In the image flat part, since the difference between frames is small and it is often difficult to detect motion, only the image flat part is detected and separately encoded as in the embodiment of the present invention. By doing so, it is possible to more reliably suppress the generation of the moving image false contour also in this portion.

FIG. 12 shows a method of controlling the image signal encoding method based on the detected amount of motion of the image and the level change degree image of the image in the screen in the third embodiment. As shown in FIG. 12, when both the detected motion amount and the degree of change of the in-screen image level are “large”, a moving image pseudo-contour appears strongly, so moving image coding is adopted. Further, when the change in the in-screen image level is large but the detected amount of motion is small, the still image coding is performed because it is certain that the region is a still image region. Since the part of the screen where the degree of change in the image level is small can be a still image part and a flat part of the moving image, the generation of a moving image pseudo-contour at the image signal level in this area can be considered. Flat part coding that can be suppressed is adopted.

As described above, according to the present embodiment, in addition to the still image portion and the moving image portion of an image, even in a flat image portion where it is difficult to distinguish between a still image and a moving image, a moving image pseudo contour is suppressed. can do.

(Embodiment 3) Embodiment 3 of the present invention (claims 1 to 19, 22 to 25) will be described below with reference to the drawings. The description of the first embodiment of the present invention and the same parts as those of the first embodiment of the present invention will be omitted, and only the parts that are essentially different from those will be described. The third embodiment has the functions of the first and second embodiments,
It is an object of the present invention to smoothly shift an encoding method at a switching boundary between a moving image encoding method, a still image encoding method, and a flat portion encoding method.

FIG. 13 differs from FIG. 6 in that combination determination circuit 42 is configured to output transition area signal 43 in addition to the conventional selection output, and that clock pulse input 83 Line pulse input 8
4. A field pulse input 85 is provided.

As in the case of FIG. 6, the combination judging circuit 42 judges the area of each of the moving image portion, the still image portion, and the flat image portion of the input image signal by determining the motion, the degree of inclination of the image, the degree of change of the signal, and the like. Do from. In addition, a boundary portion between these regions is detected, and a transition region signal 44 is output in addition to the region selection signal 43. The selection circuit 52 selects a coded signal according to each region of the moving image portion, the still image portion, and the flat image portion of the input image signal. The coding method is alternately switched at a boundary portion in units, lines, and frames. As a result, even if the coding method is switched in a portion where the change in the image signal is small, the switching operation is inconspicuous and the coding method can be switched smoothly for each area.

As described above, according to the present embodiment, the coding method can be smoothly shifted at the switching boundary between the moving picture coding method, the still picture coding method, and the flat part coding method.

(Embodiment 4) Embodiment 3 of the present invention (claims 1 to 22) will be described below with reference to the drawings. The description of the first embodiment and the same parts as those of the first embodiment will be omitted, and only the parts that are essentially different from those will be described.

In the third embodiment, in addition to the function of the second embodiment, the shape of a region detected as an image flat portion is shaped and the image signal in this region is encoded, thereby making unnecessary coding. It is intended to suppress the occurrence of a moving image false contour which is perceived as noise by suppressing the switching of the conversion method.

In FIG. 14 showing the plasma display according to the third embodiment, the difference from the case of FIG. 6 is that an isolated point removing circuit 75 is provided after the conventional image flat portion detecting circuit 36, and That is, the limiters 76 are provided before the flat portion coding circuit 71, respectively.

The signal representing the image flat portion detected by the image flat portion detection circuit 36 may have a small-area hollow portion inside the region or may have a shape of an elongated region in the peripheral portion. . If the coding method is switched while the shape of the image flat portion remains as such, there is a possibility that these unique points may be observed as noise. Therefore, an unnecessary region is removed by the isolated point removal circuit 75 in the output of the image flat portion detection circuit 36, and the coding method is switched unnecessarily by shaping the shape of the region detected as the image flat portion. And the frequency of perceived noise is reduced.

A limiter 76 is provided in front of the flat portion coding circuit 71, and in a region handled as a flat image portion by the flat portion coding circuit 71, a range in which the generation of a moving image pseudo contour is suppressed to a predetermined value or less. The image signal level.
By doing so, even if there is a sudden signal that greatly deviates from the average distribution of the signal in the flat portion in the region detected as the flat portion, by clipping this portion, The signal level inside the flat area falls within a predetermined range, and it is possible to suppress the generation of the false contour of the moving image.

The limit range of the signal level in the limiter 76 can be linked with the flat part encoding method determined by the distribution determination circuit 40. That is, when the encoding method in the image flat part complies with the rule shown in FIG. 10, the upper limit value of the limiter 76 is set to “183” and the lower limit value is set to “96”. By providing the limiter and encoding the image flat part in this way, the image signal in the image flat area can be limited to a signal with less occurrence of a moving image false contour.

As described above, according to the present embodiment, it is possible to suppress the generation of the pseudo contour of the moving image due to the isolated signal in the flat portion of the image, and to improve the effect of reducing the pseudo contour of the moving image in the flat portion of the image. can do.

In the first to fourth embodiments, the number of subfields and the luminance weight of each subfield have been described by way of example. However, the present invention is not limited to this. In particular, when the number of sub-fields can be increased, a sub-field having a large luminance weight can be divided into a larger number of sub-fields having a small luminance weight. Needless to say, the size of the image can be reduced, and a higher-quality moving image can be displayed.

Also, the order of the subfields and the encoding method are not particularly limited to those described in the embodiment, and can be modified within the scope described in the claims of the present invention.

[0114]

As described above, according to the multi-tone image display device of the present invention, the following effects can be obtained.

The present invention (claim 1) provides subfield coding based on various combinations of a signal level change degree of an input image signal in a screen and a signal level change degree of the input image signal in a time direction. The encoding method in the means is determined. For this reason, in image parts where moving image pseudo contours are likely to occur, such as a combination of a specific image pattern and a specific image motion, a sub-field encoding method that prioritizes the elimination of moving image pseudo contours is used. Accordingly, in an image portion where a moving image false contour does not occur, a subfield encoding method giving priority to gradation display characteristics can be used, and good image display can be realized in both still image display and moving image display.

Further, the present invention (claim 2) is characterized in that a value approximated by a temporal change value of each pixel of the input image signal is used as an approximate value of the amount of movement of the line of sight. Can easily be detected as a value approximating the movement of the line of sight when observing.

Further, the present invention (claim 3) is characterized in that a value approximated by a motion vector value in a unit of a plurality of pixels detected from the input image signal is used as an approximate value of the amount of movement of the line of sight. In addition, using a technique such as block matching, it is possible to detect a value approximating the movement of the line of sight.

Further, according to the present invention (claim 4), a value obtained by correcting a temporal change value of each pixel of an input image signal with an edge component of the input signal is used as an approximate value of the amount of movement of the line of sight. The feature is. For this reason, it is possible to prevent the slight movement of the image at the edge portion of the image from being converted into a large temporal change, and to accurately approximate the movement amount without excessively evaluating the movement amount at the edge portion of the image. can do.

The present invention (claims 5, 6, 9, 10)
Compensates for the amount of movement of the line of sight according to the encoding method in the subfield encoding means, so that it is possible to evaluate the motion detection sensitivity particularly at a signal level portion where a moving image false contour is likely to occur significantly. In addition, it is possible to provide a means for appropriately detecting a motion and preventing a false contour of a moving image from occurring, thereby realizing high-quality image display.

Further, according to the present invention (claims 7 and 8), since a candidate for an image portion in which a moving image pseudo contour is likely to be generated is calculated from the inclination of the image, a moving image pseudo contour is easily generated. An image part can be obtained.

Further, according to the present invention (claims 11 to 13), a representative value, a maximum value, and a minimum value in a set area where an image signal level is in a substantially constant range in a screen of an input image signal are determined. Since it is obtained, control for encoding the image signal in this area while suppressing the generation of the moving image false contour becomes possible.

Further, the present invention (claim 14) is characterized in that an edge component of the input image signal is used as the degree of change in the signal level of the input image signal in the screen.
For this reason, it is possible to determine a subfield encoding method by specifically detecting a case where there is a sharp edge component and the occurrence of a moving image false contour is relatively inconspicuous visually.

Further, the present invention (claim 15) is characterized in that the signal level change degree of the input image signal in the time direction is a value obtained by arithmetically operating an image of a predetermined plurality of fields. With this value, the movement of the line of sight can be relatively easily approximated, and the subfield encoding method can be determined according to the movement of the image.

Further, according to the present invention (claim 16), a value obtained by performing an arithmetic operation on an image of a plurality of fields as a signal level change degree of the input image signal in a time direction is calculated by an edge component of the input image signal. It is characterized by being a corrected value. For this reason, when using the difference between a plurality of images as the amount of motion, it is possible to prevent the amount of motion from being overestimated at the edge portion of the image, to cause only slight image motion, If this has not happened, the subfield encoding method can be appropriately selected.

Further, according to the present invention (claim 17), in a portion where the amount of movement of the image or the amount of movement of the line of sight is small, the gradation control is preferentially given to the combination which suppresses the ON control of the subfield having a large luminance weight as much as possible. Therefore, even in a region where the motion of the image cannot be accurately detected due to some cause, the generation of the moving image false contour can be minimized.

Further, according to the encoding method of the subfield encoding means of the present invention (claim 18), the level increase of the input image signal and the light emission pattern can be achieved in a portion where a large amount of image movement or eye movement is detected. Is a coding method limited to coding in which the distribution has a monotonically increasing correlation. In such encoding, the occurrence of a moving image pseudo-contour is hardly observed. Therefore, by using this coding in a portion where the movement of the line of sight is large, the occurrence of the moving image pseudo-contour can be almost eliminated. In addition, by using an encoding method according to claim 19 in which the error between the input image signal and the display luminance is almost canceled in the neighboring pixels, the generation of the false contour of the moving image is almost eliminated. In addition, even in a portion where the movement of the image is sharp, a sufficient number of gradations can be ensured practically and a good image display can be realized.

Further, according to the present invention (claim 20), when the degree of change in the image signal level of the area of interest is small among the degrees of change in the image signal level of the input image signal, the present invention For the image signal, a signal subjected to amplitude limitation limited to a range that includes a large number of image signal levels of the region of interest is used, and the subfield encoding means in the region of interest uses Since the encoding method is configured to be an encoding that suppresses the switching of the ON control or the OFF control of the subfield having the largest luminance weight as much as possible, it is possible to suppress the switching of the encoding method unnecessarily, It is possible to suppress the generation of a moving image pseudo contour that is perceived as noise.

In the encoding method in the subfield encoding means according to the present invention (claims 22 and 23), the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is obtained. A portion that is detected to be large, a portion where the amount of movement of the observer's line of sight to the display screen of the image display device or an approximate value of the amount of movement of the line of sight is detected to be small, and a signal level change in the screen of the input image signal It is characterized in that the degree of change is changed in accordance with the part of the degree of change in the signal level of the region of interest out of the degrees. For this reason, the amount of movement of the observer's line of sight and the degree of change of the line of sight of the observer,
It is possible to determine the encoding method that organically combines the degree of change of the input image signal level, etc., and the optimal subfield encoding method by combining both the amount of movement of the observer's line of sight and the degree of change of the input image signal level Can be used.

Further, in the encoding method in the subfield encoding means according to the present invention (claims 24 and 25), the encoding method is selected so that the switching of the encoding method is not conspicuous at the boundary where the encoding method is changed. This makes it possible to perform wide and good image display in a still image and a moving image.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a plasma display according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an operation example in a combination determination circuit 4;

FIG. 3 is a diagram illustrating a configuration example of a moving image encoding circuit.

FIG. 4 is a diagram showing a conversion rule of a display signal encoding circuit 602.

FIG. 5 is a diagram showing a conversion rule in a still image encoding circuit 7;

FIG. 6 is a configuration diagram of a plasma display according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a display signal encoding method according to Embodiment 2 of the present invention.

FIG. 8 is a diagram illustrating a conversion rule in a still image encoding circuit 71 according to the second embodiment.

FIG. 9 is a diagram showing correction coefficients in a difference correction circuit 23 and a gradient correction circuit 35.

FIG. 10 is a diagram showing an example of a conversion rule in an image flat part according to the second embodiment of the present invention.

FIG. 11 is a diagram showing another example of a conversion rule in an image flat part according to the second embodiment of the present invention.

FIG. 12 is a diagram showing an operation example in the combination determination circuit 4;

FIG. 13 is a configuration diagram of a plasma display according to a third embodiment of the present invention.

FIG. 14 is a configuration diagram of a plasma display according to a fourth embodiment of the present invention.

FIG. 15 is a diagram showing a principle of generating a moving image false contour in a conventional plasma display.

FIG. 16 is a diagram showing an example of a pattern image in which two levels are adjacent to each other;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 input image signal 2 gaze motion detection circuit 3 image level change detection circuit 4, 41, 42 combination determination circuit 5, 51, 52 selection circuit 6, 61 video encoding circuit 7, 71 still image encoding circuit 9, 90 subfield Control circuit 10, 100 Plasma display 21 Frame memory 22 Difference detection circuit 23 Difference correction circuit 24 Edge correction circuit 31 Horizontal inclination detection circuit 32 Vertical inclination detection circuit 33 Edge detection circuit 34 Two-dimensional inclination detection circuit 35 Slope correction circuit 36 Image flat part detection circuit 37 Maximum value detection circuit 38 Representative value detection circuit 39 Minimum value detection circuit 40 Distribution judgment circuit 43 Area selection signal 44 Transition area signal 75 Isolated point removal circuit 76 Limiter 81 Flat part coding circuit 83 Clock pulse input 84 Line pulse input 85 Field pulse input 601 Addition circuit 602 Display signal encoding circuit 603 Display error detection circuit 604 to 607 Delay circuit 608 to 611 Coefficient circuit

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H04N 5/66 G06F 15/68 320A

Claims (25)

[Claims] 1. A sub-field encoding means for dividing one field of an input image signal into a plurality of sub-fields and encoding the luminance of each of the sub-fields to an on state or an off state for each of the sub fields. An image display device for displaying an image by controlling the gradation by the subfield encoding means, wherein the movement of the line of sight or the movement of the line of sight on the display screen of the observer when displaying a moving image on the image display device And an image signal level change degree in the screen of the input image signal,
A multi-tone image display device, wherein an encoding method in the sub-field encoding means is determined based on a combination of the input image signal and a degree of change in an image signal level in a time direction. 2. The multi-tone image display device according to claim 1, wherein the approximate value of the amount of movement of the line of sight is a value approximated by a change value in the time direction of each pixel of the input image signal. . 3. The multi-tone image display according to claim 1, wherein the approximate value of the amount of movement of the line of sight is a value approximated by a motion vector value of a plurality of pixels detected from the input image signal. apparatus. 4. The method according to claim 1, wherein the approximate value of the amount of movement of the line of sight is a value obtained by correcting a change value in the time direction of each pixel of the input image signal with an edge component of the input signal. The multi-tone image display device according to the above. 5. The approximate value of the amount of movement of the line of sight is a value obtained by correcting a temporal change value of each pixel of the input image signal by a correction value determined by an encoding method in the subfield encoding means. 2. The multi-tone image display device according to claim 1, wherein: 6. A correction value determined by an encoding method in said subfield encoding means is a temporal value of a luminance value displayed when an input image signal is continuously changed according to said encoding method. 6. The multi-tone image display device according to claim 5, wherein the degree of discontinuity is a degree of discontinuity. 7. The multi-tone image display device according to claim 1, wherein the degree of change in the image signal level of the input image signal in a screen uses a gradient of the image signal level of the input image signal. 8. The inclination of the image signal level of the input image signal is obtained from the horizontal or vertical inclination of the input image signal, or the horizontal and vertical inclinations of the input image signal. 8. The multi-tone image display device according to claim 7, wherein the inclination is calculated. 9. The degree of change in the image signal level of the input image signal within the screen is determined by adjusting the gradient of the image signal level of the input image signal by a correction value determined by an encoding method in the subfield encoding means. The multi-tone image display device according to claim 7 or 8, wherein the corrected value is a corrected value. 10. A correction value determined by an encoding method in said subfield encoding means is a time of a luminance value to be displayed when said input image signal is continuously changed according to said encoding method. 10. The multi-tone image display device according to claim 9, wherein the degree of continuity is a degree of continuity. 11. The degree of change in the image signal level of the input image signal in the screen includes a representative value of the image signal level in a predetermined area of a pixel area temporally or spatially close to a pixel of interest in the input image signal. 2. The multi-tone image display device according to claim 1, wherein the value is a value calculated from the maximum value and the minimum value. 12. An image signal level change degree of the input image signal in a screen is calculated from a representative value, a maximum value, and a minimum value of image signal levels in a flat region of an image including a pixel of interest in the input image signal. 2. The multi-tone image display device according to claim 1, wherein the value is a value. 13. The image signal level change degree of the input image signal in a screen is determined by detecting a flat region of an image from an image including a pixel of interest in the input image signal, and determining a shape isolated from the detected flat region. 2. The multi-tone image display device according to claim 1, wherein the multi-tone image display device is a value calculated from a representative value, a maximum value, and a minimum value of an image signal level of a region from which the pixel region is removed. 14. The multi-tone image display device according to claim 1, wherein the degree of change in the image signal level of the input image signal in the screen is an edge component of the input image signal. 15. The multi-tone image display device according to claim 1, wherein the degree of change in the image signal level in the time direction of the input image signal is a value obtained by arithmetically operating images of a plurality of fields. . 16. The image signal level change degree of the input image signal in the time direction is a value obtained by correcting a value obtained by arithmetically operating an image of a plurality of fields by an edge component of the input image signal. The multi-tone image display device according to claim 1, wherein 17. An encoding method in the subfield encoding means, wherein a portion having a small amount of movement of the line of sight of the observer with respect to the display screen of the image display device or an approximate value of the amount of movement of the line of sight has a large luminance weight. 2. The multi-tone image display device according to claim 1, wherein the tone control is performed with priority given to a combination that suppresses the on-control of the sub-field as much as possible. 18. An encoding method in the subfield encoding means, wherein the movement amount of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the movement amount of the line of sight is detected largely. 2. The multi-tone image display device according to claim 1, wherein the encoding method is limited to encoding in which the level of the input image signal and the distribution of the light emission pattern have a strong monotonically increasing correlation. 19. An encoding method in the sub-field encoding means, wherein, in a portion where the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is detected largely, The coding is limited to coding in which the level increase of the input image signal and the distribution of the light emission pattern have a strong monotonically increasing correlation, and the coding is performed so that an error between the input image signal and the display luminance is almost canceled in adjacent pixels. 2. The multi-tone image display device according to claim 1, wherein a conversion method is controlled. 20. When the degree of change in the image signal level of the region of interest is small among the degrees of change in the image signal level of the input image signal, the image signal of the input image signal is focused on. Of the image signal level of the area,
Using an amplitude-limited signal limited to a range that includes a large number, the encoding method in the sub-field encoding means in the region of interest, the ON control of the sub-field having the largest luminance weight or 2. The multi-tone image display device according to claim 1, wherein the coding is such that the switching of the off control is suppressed as much as possible. 21. An encoding method in the sub-field encoding means, wherein the degree of change in the image signal level of the region of interest is small among the degrees of change in the image signal level of the input image signal. 2. The multi-gradation image display device according to claim 1, wherein the coding is performed in such a manner that switching between on-control and off-control of a subfield having the largest luminance weight is suppressed as much as possible in a region where the luminance is weighted. 22. An encoding method in said sub-field encoding means, wherein: a portion in which an amount of movement of a line of sight of an observer with respect to a display screen of the image display device or an approximate value of the amount of movement of the line of sight is detected largely; A portion in which the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is detected to be small, and a signal of a region of interest among the degrees of change in the image signal level of the input image signal 2. The multi-tone image display device according to claim 1, wherein the change is made in accordance with a combination with a portion having a small level change. 23. An encoding method in the sub-field encoding means, wherein a large amount of movement of the observer's line of sight with respect to the display screen of the image display device is detected, and a part where the degree of change in the input image signal level is large is used. 1 is selected, the second coding method is selected in a portion where the degree of change in the input image signal level is small, and the third coding method is selected in a portion where the amount of movement of the line of sight of the observer is detected to be small. 21. The multi-tone image display device according to claim 20, wherein a method is selected. 24. An encoding method in said subfield encoding means, comprising: a portion in which an amount of movement of a line of sight of an observer with respect to a display screen of the image display device or an approximate value of the amount of movement of the line of sight is detected largely; A portion where the amount of movement of the line of sight of the observer with respect to the display screen of the image display device or the approximate value of the amount of movement of the line of sight is detected to be small, and a region of interest of the signal level change degree within the screen of the input image signal 2. The multi-tone image display device according to claim 1, wherein the signal level is changed by a combination with a portion where the degree of change of the signal level is small and a boundary portion between them. 25. An encoding method in the sub-field encoding means, wherein a large amount of movement of an observer's line of sight with respect to a display screen of the image display device is detected, and a degree of change in an input image signal level is large. The first encoding method is selected in the image region portion, the second encoding method is selected in the second image region portion where the degree of change in the input image signal level is small, and the amount of movement of the observer's line of sight is small. 3. The method according to claim 1, wherein a third encoding method is selected in a detected third image area, and a fourth encoding method is selected in a boundary between the first to third image areas. 22
The multi-tone image display device according to the above.