JP3521591B2 - Error diffusion processing device for display device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an error diffusion processing device of a display device using a display panel having a gradation number outside the factorial display of 2. The number of gradations out of the factorial display of 2 is, for example, 12 (2 to the third power is 2
4) and 28 (not 2 4 or 2 5), and the display panel means a digital display panel such as PDP (plasma display panel) or LCD (liquid crystal display panel).

[0002]

2. Description of the Related Art Recently, PDPs and LCDs have been attracting attention as thin and lightweight display devices. This PDP drive system is completely different from the conventional CRT drive system, and is a direct drive system using a digitized input video signal. Therefore, the brightness gradation emitted from the panel surface is determined by the number of bits of the signal to be handled.

PDPs are AC type and D type which have different basic characteristics.
It is divided into two types, C type. AC-type PDPs have sufficient characteristics in terms of brightness and life, but regarding gray-scale display, only a maximum of 64 gray-scale displays at the prototype level was reported, but the address / display separation type driving method (ADS) was used. A future 256-gradation method based on the subfield method) has been proposed.

In the ADS subfield method, for example, in the case of 8 bits and 256 gradations, one frame has a relative luminance ratio of 1, 2, 4, 8, 16, 32, 64, 128.
It is composed of 8 sub-fields, and 256 gradations are displayed by combining the brightness of 8 screens. Each subfield is composed of an address period for writing refreshed data for one screen and a sustain period for determining the luminance level of the subfield.

In the AC driving method as described above, as the number of gradations is increased, the number of bits in the address period as a preparation period for lighting and emitting the panel within one frame period is increased. The period is relatively short and the maximum brightness is low. In this way, since the brightness gradation emitted from the panel surface is determined by the number of bits of the signal to be handled, if the number of bits of the signal to be handled is increased, the image quality is improved, but the light emission luminance is reduced, and conversely If the number of bits is reduced, the light emission luminance is increased, but gradation display is reduced and the image quality is deteriorated.

The error diffusion process for minimizing the contrast error between the input signal and the emission luminance while reducing the bit number of the output diffusion output signal than the bit number of the input signal is a process for expressing a pseudo halftone. Yes, it is used when expressing light and shade with few gradations.

A conventional display device using a general subfield method and error diffusion processing is configured as shown in FIG. That is, the error diffusion circuit 10 performs error diffusion processing using the light emission luminance level set in the ROM 12 in advance, so that m (≦ n−) from the n-bit input video signal.
1) Obtain a spread output signal of bits. Next, the data conversion circuit 14 time-divides the m-bit diffused output signal into one frame into a plurality of sub-fields, and the display gradation number p (p = p
It is converted into a drive signal for displaying a halftone image by the PDP 16 of 2 m).

As a result, as shown in FIG. 5, although the light emission luminance level like the step of the solid line is momentarily output, the light emission luminance levels above and below the step of the solid line are actually output. Are alternately output at a predetermined ratio, so that they are recognized in an averaged state and become a corrected luminance line of y = x like a dotted line.

[0009]

However, the light emission luminance characteristic of the PDP 16 may change depending on the data to be displayed and may be different from the light emission luminance characteristic shown in FIG. 5. In such a case, as shown in FIG. However, in the method of adjusting to the typical emission luminance characteristic, there is a problem that it cannot fully adapt to the gradation characteristic, and a pseudo contour appears due to the gradation non-adaptation. In order to solve such a problem, the present applicant has already proposed a display device using a gradation adaptive error diffusion process as shown in FIG.

Further, in a case where one frame is composed of a plurality of sub-fields SF1 to SFm having different luminance relative ratios, and a combination of luminances of m screens is used to display 2 m gray scales, the luminance level of the drive signal is Is from "2 to the m-1" to "2
M-th power ”(eg, from“ 7 ”to“ 8 ”or“ 15 ”)
There is a problem that granular noise is seen on the screen corresponding to the changed portion when changing from "16" to "16". In order to solve such a problem, the present applicant has already proposed that, as shown in FIG. 7, at least two subfields of a plurality of subfields forming one frame have equal weighting. did.

That is, the display device using the gradation adaptive type error diffusion processing as shown in FIG.
The error diffusion circuit 10 obtains the emission luminance characteristic of the PDP 16 for each one or a plurality of frames based on the drive signal output from the error diffusion circuit 10.
a light emission luminance characteristic acquisition circuit 18 for outputting to a, and instead of the light emission luminance level provided from the ROM 12 of FIG. 4, the light emission luminance level is updated for each frame or every plural frames to perform error diffusion. Prevent the appearance of false contours.

Further, FIG. 7 showing a frame structure for preventing granular noise from appearing on the screen is shown in FIG. 7, in which a plurality of sub-frames constituting one frame have a relative luminance ratio of 1, 2,
Six subfields SF1, SF of 4, 4, 8 and 8
2, SF3, SF4, SF5, and SF6 are provided to prevent a large change in brightness when the brightness level changes, thereby preventing deterioration of image quality. At this time, the six subfields SF1, SF2, SF3, SF4, SF
28 with a combination of 5 and 6 screen brightness corresponding to SF6
Gradation display is performed.

A factorial of 2 as described above (eg 2 of 6)
PDP1 with a gradation number less than the power of 64 (eg 28)
Considering the case of performing error diffusion processing using 6,
In order to bring the gradation steps closer to a straight line, the ROM 12 of FIG.
A method is conceivable in which the light emission luminance level stored in advance is configured as shown in FIG. In other words, it is a method of compensating for a gradation that is insufficient in the factorial of 2 by using one gradation twice in the middle of the gradation. However, when the gradation adaptive error diffusion processing as shown in FIG. 6 is performed in response to the emission luminance characteristics as shown in FIG. 8, the following problems occur.

That is, the characteristics of the emission luminance level with respect to the drive signal of the PDP 16 are stepwise such that the same gray level in the middle is used twice as shown in FIG. 8 at regular intervals (for example, every one or multiple frames). Then, the emission brightness characteristic of the PDP 16 is obtained and the emission brightness level is updated. For this reason, at a continuous portion of the same brightness level (for example, in FIG. 8, the brightness level 32 of which the drive signal level exceeds 32 and is less than 64, or the brightness level 96 of which the drive signal level exceeds 112 and is less than 144), the pseudo gradation is generated. However, there is a problem in that it is not possible to obtain a smooth error diffusion processing result.

The present invention has been made in view of the above-mentioned problems, and pseudo halftone is performed by a gray scale adaptive error diffusion process using a display panel having a gray scale number outside the factorial display of 2. It is an object of the present invention to provide an error diffusion processing device for a display device, which is capable of producing smooth and continuous gradation when an image is displayed.

[0016]

According to a first aspect of the present invention, an m (≤n-1) -bit diffused output signal is obtained from an n-bit input video signal by performing error diffusion processing using light emission luminance characteristics. An error diffusion circuit and an m-bit diffusion output signal obtained by this error diffusion circuit are time-divided into a plurality of subfields in one frame, and the number of display gradations k (<2 to the m-th power)
Data conversion circuit for converting into a drive signal for displaying a halftone image on the display panel, and the light emission of the display panel corresponding to the preset correction luminance line Q based on the drive signal obtained by the data conversion circuit. and light emission luminance characteristic acquisition circuit for obtaining a luminance line P at regular intervals, said comprising a memory storing a preset corrected luminance line Q, the set emission luminance line P from the level 0 of the driving signal The emission luminance level gradually increases up to a level Dk corresponding to the number of display gradations k at a ratio of 1: 1, and the emission luminance level repeats the maximum luminance level for a drive signal exceeding the level Dk. set, set in the memory stored correction luminance line Q
Is set so as to intersect the level of each step of the set emission brightness level of the emission brightness line P , which increases stepwise,
The error diffusion circuit is characterized by performing an error diffusion process using the emission luminance characteristic obtained by the luminance characteristic acquisition circuit and the corrected luminance line Q set and stored in the memory.

In order to perform gradation adaptive error diffusion processing,
The light emission luminance characteristic obtained by the light emission luminance characteristic acquisition circuit at regular intervals is from the level 0 of the drive signal to the number of display gradations k.
Level Dk corresponding to (eg 12) (eg 17
Up to 6), the emission brightness level is increased stepwise at a ratio of 1: 1, and the emission brightness level is preset to repeat the maximum brightness level (for example, 176) for the drive signal exceeding the level Dk. Since it corresponds to the emission luminance line P , the same luminance level is not used twice in the staircase portion before saturation. Moreover, the correction luminance line Q used together with the light emission luminance characteristic in the error diffusion circuit is set so as to intersect with the level of each step of the set light emission luminance line P in the stepwise increasing light emission luminance level. Therefore, gradation-adaptive error diffusion can produce smooth and continuous gradation.

According to a second aspect of the present invention, in the first aspect of the invention, the data conversion circuit is obtained by an error diffusion circuit so that granular noise is not visible on the screen corresponding to the changed portion of the brightness level. The m-bit spread output signal is time-divided from one frame into a plurality of subfields including at least two subfields having the same weighting, and a halftone image is displayed on a display device having a number of display gradations k (<2 m power). Is converted into a signal for displaying.

[0019]

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of an error diffusion processing device for a display device according to the present invention. FIG. 1A shows a block diagram of the apparatus. In this figure, 20 is an error diffusion circuit for performing an error diffusion process for minimizing a density error between the input video signal and the emission brightness of the PDP 16a. . The error diffusion circuit 20 is
Alternatively, by performing error diffusion processing using the emission luminance level obtained and updated for each of a plurality of frames and the corrected luminance line Q stored and set in the memory 22 in advance, an input image of 8 (in the case of n = 8) bits is obtained. 4 from the signal (m ≦ n−1, m
= 4), it is configured to obtain a spread output signal of bits.

A data conversion circuit 14a is coupled to the output side of the error diffusion circuit 20. This data conversion circuit 1
Reference numeral 4a denotes a diffusion output signal output from the error diffusion circuit 20, and four subfields SF1, SF2, in which one frame is weighted as 4, 2, 1, 4 as shown in FIG.
The number of display gradations is 12 (k = 12) by time division into SF3 and SF4.
In the case of PDP 1), the PDP 1 is converted into a drive signal for displaying a pseudo halftone image of 176 gradations (an example of gradations less than 256 of 2 8 gradations (n = 8)).
It is configured to output to 6a.

On the output side of the data conversion circuit 14a,
A light emission luminance characteristic acquisition circuit 18a mainly including a display area calculation unit that obtains a display area ratio of one or a plurality of frames of the PDP 16a and a luminance deviation amount calculation unit that obtains a luminance deviation amount of each level is connected. . The light emission luminance characteristic acquisition circuit 18a forms a preset light emission luminance line P (line indicating the light emission luminance characteristic) as shown in FIG. 1B based on the drive signal obtained by the data conversion circuit 14a. The corresponding emission brightness characteristics of the PDP 16a for each one or a plurality of frames are obtained and output to the error diffusion circuit 20.

The set emission luminance line P is shown in FIG.
As shown in (b), from the level 0 of the drive signal to the level Dk (= 176) corresponding to the number k of display gradations, the emission brightness level is 0, 16, 32, ... 176 at a ratio of 1: 1. Drive signal (192,
268, 224, ...) The emission brightness level is set to repeat the maximum brightness level 176.

As shown in FIG. 1B, the correction luminance line Q preset and stored in the memory 22 has a level Dk (corresponding to the display gradation number k from the level 0 of the drive signal of the emission luminance line P). = 176), 0, 16, 32,
176 is set so as to intersect with the level of each step of the emission luminance level that increases stepwise.

A gamma correction circuit 24 is connected to the preceding stage of the error diffusion circuit 20. This gamma correction circuit 24
Is the level Dk of the set emission brightness line P among the emission brightness levels obtained by the emission brightness characteristic acquisition circuit 18a.
Drive signals (192, 208, 224, ...) And emission brightness levels (176, 176, 176 ...) It is intended to correct the linearity between brightness levels.

Next, the operation of FIG. 1A will be described with reference to FIG.
(B) will be described together. The error diffusion circuit 20 performs an error diffusion process using the emission luminance characteristic obtained and updated by the emission luminance characteristic acquisition circuit 18a for each one or a plurality of frames and the corrected luminance line Q preset and stored in the memory 22. Thus, from the 8 (when n = 8) bit video signal input through the gamma correction circuit 24, 4 (m =
4) obtain the spread output signal of bits.

The data conversion circuit 14a includes an error diffusion circuit 2
The diffused output signal of 0 is converted into a drive signal corresponding to the subfield display method and output to the PDP 16a. This PDP
As shown in FIG. 2, the drive signal to 16a is provided with four subfields SF1, SF2, SF3, SF4 in one frame.
Time division, and using the combination of the brightness of 4 screens,
This is a drive signal for displaying a pseudo halftone image of 176 gradations on the PDP 16a of gradation (when k = 12).

The emission luminance characteristic acquisition circuit 18a is based on the drive signal obtained by the data conversion circuit 14a.
Corresponding to the preset emission luminance line P as shown in (b), the emission luminance characteristic of the PDP 16a for each one or a plurality of frames is obtained and output to the error diffusion circuit 20. For this reason,
The error diffusion circuit 20 performs gradation adaptive error diffusion processing using the emission luminance characteristic obtained and updated for each one or a plurality of frames and the corrected luminance line Q set and stored in the memory 22.

As described above, the emission brightness characteristics obtained and updated by the emission brightness characteristic acquisition circuit 18a for performing the gradation adaptive error diffusion processing are the display gradation number 12 from the level 0 of the drive signal. Level 1 corresponding to (k = 12)
Up to 76 (Dk = 176), the emission luminance level increases stepwise at a ratio of 1: 1, and the emission luminance level repeats the maximum luminance level 176 for a drive signal exceeding the level 176. Since it corresponds to the characteristic, the same brightness level is not used twice in the staircase before saturation. Moreover, the correction luminance line Q used together with the light emission luminance characteristic in the error diffusion circuit 20 is set so as to intersect with the level of the light emission luminance level that has been set stepwise in each step. Therefore, gradation-adaptive error diffusion can produce smooth and continuous gradation.

In the upper saturation part of the set emission brightness line P, the emission brightness level becomes the maximum brightness level 176 for the drive signal levels (192, 208, 224, ...) Exceeding the drive signal level 176. Since it is set to repeat, the light emission luminance characteristic acquisition circuit 18 corresponds to this.
Although the upper part of the emission luminance characteristic obtained and updated by a is saturated, the linearity of the upper saturation part is corrected in advance by the gamma correction circuit 24, so that a predetermined gradation can be obtained.

In the above embodiment, a gamma correction circuit is provided, and the relationship between the drive signal of the PDP corresponding to the upper saturation portion of the set emission brightness line P and the emission brightness level is gamma corrected to obtain a predetermined gradation. Although the present invention is configured so as to be obtained, the present invention is not limited to this, and a gamma correction circuit may be omitted. It should be noted that the difference in gradation at the high brightness level is not easily perceived by human eyes.

In the above embodiment, in order to prevent granular noise from being seen on the screen corresponding to the portion where the brightness level changes, as shown in FIG. 2, one frame is divided into two subfields SF1 having the same weight, The case of time division into four subfields SF1 to SF4 including SF4 has been described, but the present invention is not limited to this, and one frame can be used for time division into a plurality of subfields.

For example, as shown in FIG. 3, one frame is divided into two sets of subfields (SF1 and SF6, which have the same weighting) in order to prevent granular noise from being seen on the screen corresponding to the brightness level changing portion. It is also possible to use a time-divided subfield including six subfields SF1 to SF6 including SF2 and SF5). Alternatively, it is also possible to use one frame time-divided into a plurality of subfields having different weightings.

In the above embodiment, the display panel is the PDP.
However, the present invention is not limited to this, and can be applied to the case of a digital display panel (for example, LCD).

[0035]

According to the present invention, in a device for displaying a pseudo-halftone image on a display device by the subfield method and the gradation adaptive error diffusion process, the gradation adaptive error diffusion process is performed at regular intervals. The emission luminance characteristics obtained and updated (for example, for each one or a plurality of frames) have emission luminance levels from the level 0 of the drive signal to the level Dk (for example, 176) corresponding to the display gradation number k (for example, 12). It corresponds to a preset emission luminance characteristic that the emission luminance level repeats the maximum luminance level (for example, 176) for a drive signal that exceeds the level Dk and increases stepwise at a ratio of 1: 1. Therefore, the same brightness level is not used twice in the staircase before saturation. Moreover, the correction luminance line used together with the light emission luminance characteristic in the error diffusion circuit is set so as to intersect the level of each step of the set light emission luminance characteristic which gradually increases. Therefore, smooth and continuous gradation can be generated by gradation adaptive error diffusion.

The data conversion circuit time-divides the m-bit diffused output signal obtained by the error diffusion circuit into a plurality of subfields including two subfields having at least equal weighting, and the number of display gradations k (<2 to the mth power)
When the display device is configured to convert into a signal for displaying a halftone image, it is possible to prevent granular noise from being seen on the screen corresponding to the portion where the brightness level changes.

Among the emission brightness characteristics obtained by the emission brightness characteristic acquisition circuit, the higher order of the emission brightness characteristics corresponding to the emission brightness characteristics between the drive signal and the emission brightness level exceeding the set emission brightness level Dk. Is saturated, but the linearity of the upper saturation part is corrected in advance by the gamma correction circuit, so that a predetermined gradation can be obtained.

[Brief description of drawings]

1A and 1B show an embodiment of an error diffusion processing device for a display device according to the present invention, wherein FIG. 1A is a block diagram of the device, and FIG. 1B is a gradation adaptive error diffusion by the device of FIG. FIG. 9 is a light emission luminance characteristic chart set in advance corresponding to the light emission luminance characteristics obtained and updated by the processing.

2 illustrates the structure of one frame time-divided by a data conversion circuit when the number of display gradations k of the PDP of FIG.
It is explanatory drawing of the drive sequence in 2-gradation display.

3 is an explanatory diagram of a drive sequence in 28 gradation display by a subfield method when the number of display gradations k of the PDP in FIG. 1 is 28;

FIG. 4 is a block diagram of an error diffusion processing device of a display device using a general subfield method and an error diffusion process.

FIG. 5 is a characteristic diagram showing a typical example of emission luminance characteristics.

FIG. 6 is a block diagram of an error diffusion processing device of a display device which performs gradation adaptive error diffusion processing.

FIG. 7 is an explanatory diagram of a drive sequence in 28 gradation display.

FIG. 8 is pre-stored in a ROM, which is conceived to bring the steps of the gradation closer to a straight line when the error diffusion process is performed in the PDP displaying the gradation number less than the factorial of 2 (for example, 12). It is a characteristic view of a light emission luminance level.

[Explanation of symbols]

10, 10a, 20 ... Error diffusion circuit, 12 ... ROM,
14, 14a ... Data conversion circuit, 16, 16a ... PDP
(Example of display device), 18, 18a ... Emission brightness characteristic acquisition circuit, 22 ... Memory (correction brightness line Q is stored),
24 ... Gamma correction circuit, Dk ... Drive signal level corresponding to display gradation number k, k ... Display gradation number of PDP, P ...
Preliminarily set emission luminance line (emission luminance characteristic), Q ... Corrected luminance line preset and stored, SF1 to SF4 ... Subfield.

Front page continuation (72) Inventor Junichi Onodera 1116 Suenaga, Takatsu-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu General Co., Ltd. ) References JP-A-9-81072 (JP, A) JP-A-9-179522 (JP, A) JP-A-9-146492 (JP, A) JP-A-7-140923 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G09G 3/00-3/38

Claims (2)

(57) [Claims] 1. An error diffusion process using light emission luminance characteristics is performed to convert m (≦ n−) from an n-bit input video signal.
1) An error diffusion circuit for obtaining a bit diffusion output signal and an m-bit diffusion output signal obtained by the error diffusion circuit
A data conversion circuit that time-divides a frame into a plurality of subfields and converts into a drive signal for displaying a halftone image on a display panel with a display gradation number k (<2 to the m-th power), and this data conversion circuit Based on the obtained drive signal, the emission brightness of the display panel corresponding to the preset correction brightness line Q
And light emission luminance characteristic acquisition circuit for obtaining a line P at regular intervals, before
Note that the preset emission luminance line P has a memory for storing a preset correction luminance line Q , and the emission luminance level P set in this manner has an emission luminance level from level 0 of the drive signal to level Dk corresponding to the number k of display gradations. Level D gradually increasing at a ratio of 1: 1
For a drive signal exceeding k, the emission luminance level is set to repeat the maximum luminance level, and the corrected luminance line Q set and stored in the memory is the set emission luminance line.
The error diffusion circuit is set so as to intersect with the level of the gradually increasing emission brightness level of P , and the error diffusion circuit sets the emission brightness characteristic obtained by the brightness characteristic acquisition circuit and the corrected brightness set and stored in the memory. An error diffusion processing device for a display device, which performs an error diffusion process using a line Q. 2. A data conversion circuit, the spread output signal of m bits obtained by the error diffusion circuit, display floor to time-divided into a plurality of subfields including two subfields equal at least weighting 1 frame Key k (<2 to the m-th power)
2. The error diffusion processing device for a display device according to claim 1, wherein the error diffusion processing device is converted into a signal for displaying a halftone image on the display device.