DE10320299B4 - Method and device for improving the gray value representation of a pulse-width-controlled image display device - Google Patents

Abstract

Method for improving the gray scale representation in the case of a pulse-width-controlled image display device, in which the time interval available for an image representation is divided into successive differently weighted part-time intervals and the luminance signals associated with the pixels of the image to be displayed are generated by conversion into activation sequences assigned to the part-time intervals, the activation sequences respectively given numbers of sustain pulses and the number of sustain pulses for all activation sequences that are within a time interval for the representation of an image, is variable, characterized in that in an analysis of the image to be displayed, the maximum occurring brightness is determined, and that falls below a predetermined maximum brightness value as a function of the respectively found brightness, a signal is generated which the number of Sus tain pulses for activation sequences which lie within a time interval for the representation of an image, by a degree associated with the brightness changes, and that is determined when exceeding the predetermined maximum brightness value in an analysis of the image to be displayed, whether contiguous areas are present in the image to be displayed Whose brightness and areal extent are within predetermined ranges of values, and generating a signal that matches the number of sustain pulses for activating sequences that lie within a time interval for the representation of an image, depending on the respectively found value range pairs assigned degree changed.

Description

The invention relates to a method and a device for improving the gray value representation of a pulse width-controlled image display device.

Such a method and apparatus are used, for example, in plasma displays, which in the future will supplement or replace the color picture tubes currently used in higher-quality television sets. In the context of color picture tubes, the user of high quality televisions has been accustomed to a flicker free display since the late 1980's due to the 100Hz technology.

From the magazine Radio Television Electronics RFE, Issue 2, 1997, pages 18-20, a plasma display is known, which consists of two glass plates with matrix-like electrodes, between which there is a noble gas mixture. The image information is not displayed line by line in plasma displays as in cathode-ray tubes, but in full screen. Since the individual pixels can not be switched on and off individually at arbitrary times in the case of a plasma display, the activation of the pixels for the entire display must take place in an activation pass.

The activation of a plasma display takes place in several phases: an addressing or initialization phase, a holding or activation phase and a deletion phase.

In the addressing or initialization phase, all cells of the plasma display are electrically precharged, which are to be activated in the subsequent hold or activation phase. In the last step, the delete phase, the preloaded cells are unloaded again, the image information is deleted.

The time interval available for displaying a television picture is decomposed into part-time intervals of different duration or different weighting, during which a predetermined activation sequence is selected as a function of the brightness value of a respective picture element. This corresponds to a single or multiple illumination of the respective pixel during the time interval available for image display, wherein each illumination is assigned a predetermined period of time.

Such known plasma displays are manufactured and sold, for example, by the companies Fujitsu and NEC.

From the DE A1 198 33 597 For example, a method and apparatus for flicker reduction in pulse width controlled image display devices are known, especially in a color plasma display. Such a color plasma display serves, for example, to display television pictures. The color plasma display is controlled by means of a pulse width modulator, wherein the duration of a television picture is broken down into a series of subpictures or part time intervals, which are displayed one after the other. For flicker reduction, in particular a 50 Hz flicker reduction, the order of the part-time intervals and / or the activation sequences of the part-time intervals is specified such that the flickering of the images to be displayed is minimal.

Furthermore, from the DE-A1 198 37 307 a motion detector dependent change in the order of the part-time intervals known. In the presence of motions, the order of the part-time intervals is chosen such that motion artifacts are avoided. Otherwise, the order of the part-time intervals is selected such that 50 Hz flickering is reduced.

Furthermore, in the context of plasma displays, it is already known to detect the brightness of an image to be displayed, to derive a maximum permissible illumination duration from the detected brightness value for each of the part time intervals of the image to be displayed, and to allow the maximum permissible illumination duration for each of the partial time intervals for a change in the detected brightness value change. This change takes place in such a way that when the dark picture content or the low brightness value is detected, the maximum permissible lighting duration in each of the part-time intervals is increased by the same time duration. If, on the other hand, the brightness detection of the image to be displayed shows that the image content is altogether brighter, then the maximum permissible illumination duration for each of the part-time intervals is reduced by a time duration which is the same for all part-time intervals.

A disadvantage of this procedure is that the contrast of the image to be displayed is reduced, since with detected high brightness of the image to be displayed, the time for the representation of light image components is reduced and dark gray image components are displayed light gray when detected low brightness of an image to be displayed the loading described is pulled upwards with a constant offset, d. H. shine longer.

From the DE 101 12 622 Finally, a method and a device for improving the gray value resolution in a pulse width-controlled image display device is known. In the process, this becomes available for an image representation Time interval divided into successive weighted part-time intervals, with lower weight part time intervals and higher weight part time intervals are provided. If it is determined by evaluating the brightness of an image to be displayed that a dark image is present, then the use of higher weighted part time intervals is waived and instead the number of low weight part time intervals is increased by using additional low weight part time intervals, with the weights of the distinguish additional part-time intervals from the weights of the first part-time intervals with low weights. This achieves an improvement of the gray value resolution in the presence of dark images. A disadvantage of this method is that in commercial plasma displays with integrated control usually the assignment of the part-time intervals to be addressed for the display of a specific gray value in the non-accessible drive circuit fixed, that is not changeable.

Color plasma displays moreover have a regulation for controlling the power consumption. The purpose of this regulation is to protect the display from destruction due to overheating. For this it is known in the context of plasma displays to detect the power consumption either by measuring the Sustainer current or by evaluating the brightness of an image to be displayed. In the latter case, a maximum permissible lighting duration is derived from the detected brightness value for each of the part-time intervals of the image to be displayed, and the maximum permissible lighting duration for each of the part-time intervals changes when the detected brightness value changes. This change takes place in such a way that when the dark picture content or the low brightness value is detected, the maximum permissible lighting duration is selected in each of the part-time intervals. If, on the other hand, the brightness detection of the picture to be displayed shows that the picture content is altogether brighter, the maximum permissible lighting duration for each of the part-time intervals is reduced by one period of time. The reduction of the lighting duration follows - depending on the integral brightness of the image to be displayed - a function that achieves a limitation of the power at the upper permissible value.

Regardless of whether the measure of power is the Sustainer current or the integral brightness of the image being displayed, it is controlled by reducing the number of Sustainer pulses per sub-interval to realize the upper limit power limit. The reduction of the number of sustain pulses per part-time interval is proportional to the duration of a part-time interval.

The big disadvantage of this procedure is that with high brightness of the image to be displayed, the time for the representation of light image components is reduced, then white turns gray. In the case of low brightness of an image to be displayed, dark gray image constituents are then displayed in light gray in turn. This is particularly unpleasant in the image impression, if the brightness over the entire image area is low, because then the brightness transitions between the individual gray levels are very large. For the picture impression, this means that the step size between two brightness levels is very large. Low-brightness images over the entire screen appear too bright.

The DE 699 35 301 T2 deals with the control of the dynamic range of a display device. Here two grayscale levels are used. The signal to be displayed is examined for the maximum level of gray scale it contains. When this maximum gray scale level in the signal reaches a first gray scale level, a first maximum brightness is displayed. If the maximum gray scale level in the signal reaches only a second gray scale level that is lower than the first gray scale level, then a second maximum brightness less than the first maximum brightness is displayed. In said document also explains which input values which effect is achieved.

The EP 0 973 331 A1 describes an arrangement for controlling the luminance in an image display device, in which the image is divided into individual blocks, for each of these blocks an average light output is determined and this value is used to control the luminance.

Based on this prior art, the present invention seeks to provide a way how in a pulse width-controlled image display device, the gray value representation can be improved while avoiding the disadvantages known from the prior art.

This object is achieved by a method whose features are specified in claim 1 or by a device having the features specified in claim 12.

Advantageous embodiments and modifications of the invention will become apparent from the dependent claims.

By the method according to claim 1 it can be achieved that, for relatively dark images, without incisive bright surfaces, the step size between the brightness levels of two successive gray levels is reduced, whereby for such Image content results in an optimized representation, without resulting in an impairment of the representation of dark images with bright surfaces.

By means of the analysis possibilities of the image to be displayed specified in the claims, the equipment required for the image analysis is kept within reasonable limits. Further advantageous embodiments and developments emerge from the features of claims 3 to 7.

By analyzing several temporally successive images according to claim 8 can be achieved that the occurrence of sudden changes in the image content, the adjustment is gradual, creating a pleasant image impression. Particularly advantageous developments are given by the features of claims 9 and 10.

With the circuit arrangement according to claim 12 can be easily achieved an improvement in the representation of dark images without incisive bright surfaces, further advantageous embodiments of the circuit arrangement are characterized in the claims 13 and 14.

Further advantageous features of the invention will become apparent from the explanation of an embodiment with reference to FIGS.

It shows:

1 a block diagram of a television receiver with a pulse width controlled plasma display display;

2 and 2a exemplary diagrams for explaining the invention and

3 to 4c Further exemplary diagrams for explaining the invention.

The method and the arrangement according to the invention are described below in connection with a television receiver, without being limited thereto. Rather, they can be used in any application that uses a pulse-width-controlled plasma display display and displays image signals such. B. Data monitors or video monitors with corresponding plasma displays.

The 1 shows a block diagram of a television receiver with a pulse width controlled plasma display display. The television receiver 1 . 2 has a television signal processing part 1 and an image processing part 2 on. The television signal processing part 1 has a first entrance 17 to which the signals of an antenna device 19 be supplied. The signals of the input 17 are sent to a high frequency and intermediate frequency processing unit 4 and an audio signal processing unit 3 forwarded. At the output of the high frequency and intermediate frequency processing unit 4 is a CVBS signal, which is an analog / digital converter 5 is supplied. The supply of an external CVBS signal is via a second signal input 20 possible, other signals, eg. B. RGB, Y / C, YUV, etc. (not shown) may of course be fed at appropriate locations, if necessary, via additional circuits in the circuit. The output signal of the analog / digital converter 5 then becomes a so-called feature box 6 directed. The feature box 6 Performs certain functions such as demodulation of the composite video signal, freeze frame, zoom, format adjustment, image sharpness optimization, picture-in-picture, etc. The resulting digital components V, U, V of an image signal 21 are sent to a digital matrix unit 8th of the image processing part 2 forwarded. The feature box 6 In addition, the conversion of the interlaced signal into a line-jump-free signal and the necessary adaptation of the signals to the screen are used 14 through line interpolation. This is done with the help of the synchronization signals 23 . 24 for vertical and horizontal synchronization.

The digital matrix unit 8th also has a connection 27 for feeding one via an external signal input 18 supplied VGA signal, which by means of an analog / digital converter 25 is converted into a digital signal. At the output of the digital matrix unit 8th is an RGB signal 22 before, with which a pulse width modulator 10 is controlled. The between the digital matrix unit 8th and the pulse width modulator arranged image analyzer 34 and its operation will be described in detail below.

From the RGB signal 22 generates the pulse width modulator 10 the drive signals 26 for an address driver 11 , For this signal generation is with the pulse width modulator 10 a memory 9 coupled. The pulse width modulator 10 has a part-time interval weighting unit which is used to weight the part-time intervals, ie to determine their order and duration. The address driver device 11 controls the individual columns of the plasma display line by line 14 at. The associated time control takes place with the aid of the time control device 13 which defines the start of the part-time intervals and the times for the addressing and activation phase. The part-time interval line control device contained in the time control serves for this purpose. The timing controller 13 is with a horizontal driver 12 connected. This horizontal driver 12 is during the activation phases active. Power is supplied by a power supply 7 ,

While the operation and structure of the television signal processing part 1 is substantially similar to that of a conventional television receiver with picture tube, is the structure of the image processing section 2 fundamentally different. The main reason for this lies in the fact that the plasma display device 14 has a digital relationship between the input and the luminance. There are thus only two states: switched on or off. Nevertheless, in order to be able to achieve a large range of different intermediate shades of gray, the in 1 illustrated image processing part 2 used for image representation of a digital time division multiplex method. This will be the RGB signals 22 divided into several part-time intervals of different durations, ie part-time intervals of different weighting.

This is done with the help of the pulse width modulator 10 , as well as the pulse width modulator driving further units, such as the timing controller 13 and a memory 9 , Due to the inertia of the human eye appear on the plasma display device 14 no longer individual image changes, but a gray value, which depends on the average activation duration. If this duration is weighted in the part-time intervals, many gray levels can be displayed with few part-time intervals. With a binary weighting (1, 2, 4, 8, ...) two can be represented with the number of part-time intervals gray levels. In order to represent as many gray levels as possible, it is thus desirable to use as many part time intervals as possible, which is not possible due to technological constraints. The pulse width modulator 10 determined by an assignment that is dependent on its input signal level, for each pixel of the image to be displayed, the order and activation of the individual part-time intervals. In the case of a binary weighting, this allocation looks like that the digital most heavily weighted bit is assigned the longest part time interval, the second highest weighted bit is the second longest part time interval, and so on.

In 2 For example, an exemplary sequence of such part time intervals as taken during a frame is shown. The time for the representation of a frame is 20 milliseconds and is subdivided into eight part-time intervals, which are also referred to as subfields (SF1 to SF8). The subfields or part time intervals are binary weighted, as stated above. With such weighting, a total of 256 shades of gray can be represented from "black" (minimum brightness) to "white" (maximum brightness).

The individual part-time intervals are subdivided into an addressing phase, as shown by way of example on the subfield SF6 28 and a sustain phase 29 , During the addressing phase 28 all pixels of the plasma display device 14 addressed, which should light up in the subfield SF6. The addressing of the individual pixels is carried out in the manner already described above. While addressing the addressing phase 28 subsequent actual activation of the display in the sustain phase 29 be using a sustain pulse generator 31 who lives in the 1 illustrated horizontal driver 12 contains a number of sustain pulses specific to the subfield - in the present example the subfield SF6 -. These sustain pulses then cause a corresponding light emission of those pixels addressed during that subfield SF6.

To the plasma display device 14 To protect against overheating is in the horizontal driver 12 a video level integrator 30 included from the RGB signal 22 generates the integral of the frame and with a signal corresponding to the integral of the frame, a sustain pulse limiter 32 so applied to the sustain pulse generator 31 then acting as a limiting, if that of the video level integrator 30 to the sustain pulse limiter 32 supplied signal exceeds a predetermined value. The limitation of the sustain pulses takes place in such a way that as in 2a exemplified the number of sustain pulses 29 in each subfield, the maximum number of sustain pulses is reduced by a predetermined percentage. Although the weighting of the part-time intervals or subfields does not change among each other as a result of this measure, the number of gray values that can be displayed remains the same, but overall there is a reduction in the luminance of the plasma display device 14 causes, evenly over all representable gray values.

The consequences for the greyscale representation resulting from the procedure described above are described below in connection with FIGS 3 and 3a explained in more detail.

Assuming that a relatively dark image on the plasma display device 14 is present in 3 a gray scale 33 representing the range of minimum luminance to maximum luminance. For simplification, it is assumed below that the range of minimum luminance to maximum luminance can be represented by 12 discrete gray values G1 to G12. If a comparatively darker picture is present, this results in the gray area actually displayed in the picture 35 only the gray levels G1 to G9 includes. The consequence of this is that the increment between each discrete Brightness values G1, G2, etc. is relatively large, which in turn causes the gray transitions are very gradual. On the other hand, if there is a very bright picture, as in 3a shown, the power limit for the plasma display device described above 14 active. As a result, the occurring luminance is uniformly reduced so that white areas appear gray, but the number of gray levels that can be displayed remains unchanged, ie 12 discrete gray levels G1 to G12 can still be displayed, but the brightness values are shifted in the "black" direction. This effect is deliberately accepted in order to make small white areas appear brilliantly white in an overall rather darker picture.

In order to improve the overall gray scale representation, in particular for those images which are relatively dark, and moreover do not contain bright areas to be displayed brilliantly, as shown in FIG 1 an image analyzer 34 used that from the RGB signal 22 and the horizontal synchronization signal 23 or the vertical synchronization signal 24 a frame to be displayed is analyzed as to whether in the image white surfaces appear that are above a predetermined surface area and whether the image to be displayed in its integral brightness and / or in its maximum brightness value corresponds to predetermined values. Depending on the image analysis described above in the image analyzer 34 this produces an output signal that he uses to sustain the sustain pulse limiter 32 to the effect that this via the sustain pulse generator 31 reduces the number of sustain pulses per sub-interval or sub-field of a frame. The reduction of the sustain pulses per subfield happens z. As a percentage of the maximum number of sustain pulses occurring within a subfield. That in the image analyzer 34 The analyzed RGB signal of a frame is then displayed on the input of the pulse width modulator 10 given and with the sustain pulse correction described above on the plasma display device 14 brought to the display.

With this procedure can be, as in 4 shown that all displayable gray values G1 to G12 are advanced in the direction of black, so that also the gray area actually shown in the image 35 , ie the gray values G1 to G9 shift in the direction of black. As a result, the step size between two successive gray values z. For example, G1 and G2 are lower and the image darker overall.

As in 4a represented the effect described intensifies if the gray area actually shown in the picture 35 only to the gray value G6 is enough, so even further moves towards dark, the step size between two gray levels z. B. G1 and G2 will be even smaller.

Join now, as in 4b is shown as an example, in a dark picture, which is a gray area 35 includes, which reaches to gray scale G6, small bright areas 36 This is detected by the image analyzer 34 and increases above the sustain pulse limiter 32 and the sustain pulse generator 31 the number of sustain pulses per sub-interval or subfield z. For example, for all subfields within this frame percentage, so that for the representation of the bright areas 36 a lighter gray G12 is available.

Be as in 4c represented, the light, especially white surfaces 37 relative to the screen area larger, there is the need to set the maximum displayable gray value G12 to the maximum luminance, to a more brilliant representation of the bright areas 37 to reach. Here, of course, the increment between two successive gray values z increases again. B. G1 and G2, but this is, as already stated, in favor of a better representation of the bright areas accepted.

If the proportion of light or white areas continues to increase, the higher power limit, which has already been mentioned above, comes into effect 1 and 2 was described.

The in conjunction with 1 described image analyzer 34 offers the possibility of analyzing the image to be displayed according to all possible criteria and, depending on the analysis result, the sustain pulse limiter 32 so act on this in turn via the sustain pulse generator 31 to limit the number of sustain pulses per sub-interval or sub-field for part-time intervals or sub-fields occurring within the analyzed frame in such a way that an improvement in the gray value representation of dark images is achieved without at the same time affecting the representation of light areas.

We already indicated, exists with the image analyzer 34 the possibility of examining the image to be displayed with regard to the presence of bright image areas, the brightness value of such bright image areas, the areal extent of such bright image areas, the maximum occurring brightness value outside these bright image areas and the integral brightness value of the image. Further investigation possibilities are of course possible. Regardless of whether all or only part of the above mentioned evaluation options are used, you will be in the image analyzer 34 or with the image analyzer 34 operatively connected, provide a memory in which reference values are stored with respect to the image analysis, which are compared with the values that the image analyzer 34 from the image analysis wins, the reference values are then in turn associated with control values with which the image analyzer 34 the sustain pulse limiter 32 charged to over this and the sustain pulse generator 31 to generate the desired number of sustain pulses within the sub-time intervals or subfields of a frame.

The above in connection with the 1 to 4c described exemplary embodiment of the method according to the invention or the arrangement according to the invention can of course be supplemented and extended by the skilled person accessible measures. So it is for example in connection with the arrangement 1 readily imaginable, because image analyzer 34 in the feature box 6 to integrate, since it is not absolutely necessary for the image analysis, the RGB signal 22 to use.

It goes without saying that the method described above for simplification in connection with a gray value representation is to be applied to the three primary colors red, green, and blue used in a video image, nothing changes thereby in the basic mode of operation.

An advantageous development of the invention is to carry out the analysis of several successive images in terms of temporal filtering. This can be z. For example, brightness jumps in successive frames can not lead to an abrupt change in the number of sustain pulses generated, but to a gradual adaptation in the sense of a transition function.

Claims (14)

Method for improving the gray scale representation in the case of a pulse-width-controlled image display device, in which the time interval available for an image representation is divided into successive differently weighted part-time intervals and the luminance signals associated with the pixels of the image to be displayed are generated by conversion into activation sequences assigned to the part-time intervals, the activation sequences respectively predetermined numbers of sustain pulses and the number of sustain pulses for all activation sequences, which are within a time interval for the representation of an image, is variable, characterized in that in an analysis of the image to be displayed, the maximum brightness is determined, and that falls below a predetermined maximum brightness value as a function of the respectively found brightness, a signal is generated which the number of Sus tain pulses for activation sequences which lie within a time interval for the representation of an image, by a degree associated with the brightness changes, and that is determined when exceeding the predetermined maximum brightness value in an analysis of the image to be displayed, whether contiguous areas are present in the image to be displayed Whose brightness and areal extent are within predetermined ranges of values, and generating a signal that matches the number of sustain pulses for activation sequences that lie within a time interval for the representation of an image, depending on the value range pairs respectively found assigned degree changed. A method according to claim 1, characterized in that additionally determines the integral brightness of the image to be displayed and compared with the largest occurring in the image displayed individual brightness value or the brightness value of the brightest occurring in the image area and the brightness difference is assigned value ranges, which in turn associated with degrees of change and, depending on the value range in which the brightness difference lies, the number of already determined sustain pulses is changed by a degree associated with this value range. Method according to one of the preceding claims, characterized in that the change in the number of sustain pulses is carried out starting from a maximum number by reduction. Method according to one of the preceding claims, characterized in that the change in the number of sustain pulses for all activation sequences which lie within the time interval for the representation of the image follows a predetermined function, such that the function for each part-time interval the degree of Indicates change. A method according to claim 4, characterized in that the function is a linear function. A method according to claim 4, characterized in that the function is a logarithmic function. A method according to claim 4, characterized in that the function is an empirically determined function. Method according to one of the preceding claims, characterized in that the analysis of a plurality of successive images in the sense of a temporal filtering is performed and In the case of sudden changes in successive pictures, the change in the number of sustain pulses generated is made incrementally. A method according to claim 8, characterized in that the stepwise variation of the number of generated sustain pulses follows a predetermined transition function. A method according to claim 9, characterized in that the course of the transition function depends on the nature of the abrupt change. Method according to one of the preceding claims, characterized in that the pulse-width-controlled image display device is a ready-made image display device which already contains the drive circuits. Device for improving the gray value representation in a ready-made pulse-width-controlled image display device, with - drive means ( 9 - 13 ) for dividing the time interval available for an image representation into successive weighted part-time intervals and for generating brightness signals associated with the pixels of the image to be displayed, wherein the control means ( 9 - 13 ) perform a conversion of the activation sequences assigned to the time intervals, wherein the activation sequences each consist of predetermined numbers of sustain pulses that are generated by a sustain pulse generator ( 31 ), which has an input which can be acted upon externally and via this input the number of sustain pulses for activation sequences which lie within a time interval for the representation of an image, can be generated, with an image analyzer ( 34 ) for detecting the image brightness ratios of the image to be displayed, wherein the image analyzer ( 34 ) detects whether images are to be displayed with predominantly dark parts of the image without larger light image areas and then generates an output signal in dependence on determined image parameters, wherein the image analyzer ( 34 ) is designed to analyze the image to be displayed in terms of the presence of bright image areas, the brightness value of such bright image areas and the areal extent of such bright image areas, - with a sustain pulse limiter ( 32 ), via its input from the image analyzer ( 34 ), such that the sustain pulse limiter sends a signal to the sustain pulse generator ( 31 ) so as to change the number of sustain pulses for activation sequences which are within the time interval for the representation of the image to be displayed by a degree predetermined by the signal. Apparatus according to claim 12, characterized in that the image analyzer via its inputs with the image signal ( 22 ) and image synchronization signals ( 23 . 24 ) of an image to be displayed is applied. Apparatus according to claim 13, characterized in that the image signal, the RGB signal ( 22 ) and the image sync signal is the horizontal sync signal ( 23 ) and the vertical synchronization signal ( 24 ).

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