KR100888577B1 - Method of processing error diffusion in a display device - Google Patents

Abstract

Provided is an error diffusion processing method of a display device that can effectively reduce image disturbance such as periodic pattern noise that appears when error diffusion processing is performed on an image having a large area of an extremely dark low gradation portion.

A plurality of lines of the effective video period are set as one area, and the one area over a plurality of screens which are a plurality of fields or a plurality of frames is set as one time area. For each line in one region, the pixel diffusing the error data is displaced aperiodically in the left and right directions. In each line of one time region, the pixel diffusing the error data is displaced aperiodically in the left and right directions. The displacement amount may be a predetermined fixed value and may not necessarily be symmetrical.

Error diffusion processing method, inverse gamma correction circuit, display device, PDP

Description

Error diffusion processing method of display device {METHOD OF PROCESSING ERROR DIFFUSION IN A DISPLAY DEVICE}

1 is a block diagram showing an embodiment of a display device using the error diffusion processing method of the present invention.

FIG. 2 is a block diagram showing a specific configuration example of the error diffusion processing circuit 3 in FIG. 1.

3 is a view for explaining a preferred example of the error diffusion processing method of the present invention.

4 is a view for explaining a preferred example of the error diffusion processing method of the present invention.

5 is a view for explaining a preferred example of the error diffusion processing method of the present invention.

6 is a view for explaining a preferred example of the error diffusion processing method of the present invention.

7 is a view for explaining the error diffusion processing method of the present invention.

8 is a view for explaining the error diffusion processing method of the present invention.

9 is a view for explaining the error diffusion processing method of the present invention.

10 is a diagram showing a conventional example.

※ Explanation of codes for main parts of drawing

1: Image signal processing circuit 2: Inverse gamma correction circuit

3: error diffusion processing circuit 4: PDP

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an error diffusion processing method used in a display device, and in particular, a plasma display panel display device (PDP), a field emission display device (FED), a digital micromirror device (DMD), an electroluminescence display (EL). The present invention relates to an error diffusion processing method of a display device capable of reducing image quality disturbance caused by multi-gradation processing by an error diffusion process.

Among display devices for displaying video signals, for example, a matrix display device such as a PDP for dividing one field into a plurality of subfields for gray scale display, an FED for gray scale display by pulse width modulation (PWM), and even a DMD. According to the driving method, an image can be represented only with a digitally limited gradation number.

Normally, in television broadcasting or the like, in which a receiver is assumed to be a cathode ray tube (CRT), gamma characteristics are preliminarily performed on the transmitter side, and linear gray scale characteristics are in addition to the inverse gamma characteristics of the CRT on the receiver side. However, in the above display device which displays images with digitally limited gradation numbers, unlike the CRT, the display device itself has a linear gradation characteristic. Therefore, in order to display an image with the same gradation characteristics as a CRT display device, which is commonly used, it is necessary to perform an inverse gamma correction process of 2.2 power on the input video signal of the display device and return the image to a linear gradation characteristic. .

On the other hand, in these display devices, the number of grayscales (bits) of the input signal may be larger than the number of grayscales (bits) that can be expressed by the display device. In addition, the number of gray scales (bits) represented by the display device may be intentionally reduced to the number of gray scales (bits) of the input signal.

In addition, when the inverse gamma correction circuit performs the inverse gamma correction process to return the linear gray scale, the number of bits may be increased once than the number of bits that can be represented by the display device. This is for the following reason. When the inverse gamma correction process is performed to return to linear gradation, the number of gradations of low luminance level is damaged, which sometimes causes image quality disturbance due to the loss of continuity of gradation. In particular, in the case of the PDP, one field is constituted by a plurality of subfields having different weights of light emission amounts, and a plurality of subfields are selected to express gradation.

Therefore, depending on the selection situation of the subfield, the visual luminance difference with respect to the adjacent gray scales becomes large, and as a result, an image quality disturbance of a pseudo contour may occur. Therefore, in order to prevent the gradation from being damaged as much as possible, an inverse gamma correction process is performed at a bit number higher than the number of bits of the original signal, and the number of bits is raised and output.

In this way, when the number of bits of the input video signal or the number of grayscales (first number of bits) of the video signal output from the inverse gamma correction circuit is larger than the number of grayscales (second number of bits) represented by the display device, There is a need to reduce the gradation number (bit number). If the gradation number (bit number) is reduced, the gradation is damaged. Therefore, multi-gradation processing is performed by using the error diffusion method.

The multi-gradation processing by the error diffusion method is performed as follows as an example in order to obtain an image corresponding to the first number of bits exceeding the digitally limited second number of bits. In Fig. 10, P is one of three dots constituting the pixel of interest, and is a dot having a gradation number that cannot be expressed as it is in the second bit number. A is the right side dot, B is the bottom left dot, C is the dot just below, and D is the right bottom dot. As shown in FIG. 10, by spreading the first bit number and the second bit number that cannot be expressed in the dot P of interest by adding a constant weight to the plurality of peripheral dots A to D, the image corresponding to the first number of bits in appearance is obtained. It is a general method to process multi-gradation as much as possible.

For example, in the case where the display device has only 8 bits of gradation capability, and the gradation display by the upper 8 bits of the 12 bits of dot data, a constant weight is added to the remaining lower 4 bits of dot data and the surrounding dots By spreading to A to D, gradation display equivalent to 12 bits is executed by using the visual integration effect. In Fig. 10, 7/16, 3/16, 5/16, and 1/16 attached to the peripheral dots A to D are examples of error diffusion coefficients indicating the degree of weight. In addition, a common error diffusion coefficient for the three primary colors signals R, G, and B is used.

As an error diffusion processing method of a conventional display device, there is a source described by the present applicant and that described in Japanese Laid-Open Patent Publication No. 2002-135608. According to the invention described in the above publication, error diffusion is performed by changing the diffusion location of error data to a pixel located at least one line behind the pixel of interest with respect to at least one of the R, G, and B signals, or by changing each line. The probability of occurrence of image quality disturbance such as periodic pattern noise that appears when the processing is performed is reduced to realize high quality display.

In the case of the display device described above, in particular a PDP, by performing the multi-gradation processing by the error diffusion method as described above, the number of external tones is increased and the quality contour of the pseudo contour is reduced. have. By the way, conventionally, the number of bits used for error diffusion for the three primary colors signals R, G, and B is used as the common number of bits, and the common error diffusion coefficient is used. When displaying, there is a problem that image quality disturbance such as periodic pattern noise peculiar to error diffusion may occur.

In addition, performance of display devices such as PDPs is continuously improved due to improvement of the structure of the panel, the material constituting the inside of the panel, and the like, and the high luminance of the panel is being advanced. For this reason, there is a tendency for image quality disturbance such as periodic pattern noise peculiar to the error diffusion to become more and more prominent. In particular, it has been found that there is a problem that the image quality deteriorates further as the panel becomes higher in the image in which there are many low gradations.

The invention described in Japanese Laid-Open Patent Publication No. 2002-135608 can usually solve these problems, but it has been found that the following new problems exist. Even if the diffusion place of the error data is changed every R, G, B or line, in the invention described in the above publication, the diffusion place is regularly changed, and the emission probability (light emission count) of each dot with respect to a certain display area becomes unbalanced. As a result, the difference in shade between the dots with high light emission and the dots with low light emission is assured, and the visual luminance difference between adjacent dots is increased. And in the image in which the area of the extremely dark low gradation part is large, S / N of a dark part is bad and a lot of noise feeling is felt.

In addition, in the case of a still picture in which a very small level video signal is constantly present in the entire screen, the light emitted by error diffusion occurs at regular intervals depending on the signal level. The dot is in a state having two values of non-dots, causing an image quality disturbance that becomes a bit line image of vertical lines or diagonal lines, or becomes a granular still image. In the case of a two-dimensional image such as a printed matter, even if it is a granular still image, there is no problem. However, in the case of a display device that handles a three-dimensional image, especially in a television application, when the image is a granular still image, there is no sense of discomfort in the conventional CRT display. It is not desirable to feel.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and the display can effectively reduce image disturbance such as periodic pattern noise which appears when error diffusion processing is performed on an image having a large area of an extremely dark low gradation part. An object of the present invention is to provide an error diffusion processing method of a device.

The present invention is directed to a plurality of dots that form color components when a video signal having a first number of bits is reduced to a second number of bits having a smaller number of bits than the first number of bits in order to solve the problems of the prior art described above. The pixel of interest is located in error data obtained by multiplying a predetermined error diffusion coefficient by at least a part of the lower bits of the first number of bits, which is the difference between the first number of bits and the second number of bits in each pixel of interest. In an error diffusion processing method of a display device in which a plurality of peripheral pixels including pixels located in a line behind a line are diffused, when at least a part of a plurality of lines in an effective video period of the video signal are defined as one region, Within this region, the position in the line direction of the pixel of interest is a reference position, and at least one dot of the pixel for diffusing the error data is positioned on the reference position. In this one time area, when the one area that spans a plurality of lines or a plurality of frames, which is aperiodic, is shifted aperiodically within the range of the preset number of pixels in the left and right directions, At each line, at least one dot of a pixel that diffuses the error data is displaced for each screen non-periodically within a range of preset number of pixels in the left and right directions from the reference position. To provide a treatment method.

EMBODIMENT OF THE INVENTION Hereinafter, the error diffusion processing method of the display apparatus of this invention is demonstrated with reference to attached drawing. Fig. 1 is a block diagram showing an embodiment of a display device using the error diffusion processing method of the present invention. Fig. 2 is a block diagram showing a specific configuration example of the error diffusion processing circuit 3 in Fig. 1, Figs. Is a view for explaining a preferred example of the error diffusion processing method of the present invention, Figures 7 to 9 are views for explaining the error diffusion processing method of the present invention.

In this embodiment shown in FIG. 1, the case where PDP is used as a matrix type display device in which an image can be represented only by a digitally limited gradation number is shown. Of course, the display device of the present invention is not limited to the PDP. In Fig. 1, video signals of three systems composed of R, G, and B signals as color components are input to the video signal processing circuit 1. The video signal processing circuit 1 performs various video signal processings on these video signals and inputs them to the inverse gamma correction circuit 2. The R, G, and B signals are, for example, 8-bit digital signals, that is, signals having 256 gray levels.

The inverse gamma correction circuit 2 performs inverse gamma correction processing having the same characteristics on the inputted R, G, and B signals, respectively, and outputs as a digital signal of 12 bits, that is, a 4096 gray level signal. The output of the 8-bit digital signal as the 12-bit digital signal is to prevent the gray level from being damaged by the inverse gamma correction process as described above.

The R, G, and B signals output from the inverse gamma correction circuit 2 are input to the error diffusion processing circuit 3. The error diffusion processing circuit 3 is composed of an R error diffusion processing circuit 3R, a G error diffusion processing circuit 3G, and a B error diffusion processing circuit 3B. Input to error diffusion processing circuits 3R, 3G, 3B. The error diffusion processing circuits 3R, 3G, and 3B perform error diffusion processing on each of the inputted R, G, and B signals and output them. That is, error data, for example, which has given a constant weight to the lower 4 bits in the 12-bit digital signal, is spread to the upper 8 bits and output as an 8-bit digital signal.

At this time, when the error data is diffused to the dots of each pixel located at the line (at least one line behind the line) behind the line where the pixel of interest is located, as shown in pixels B, C, and D in FIG. Instead of making the place constant, the pixels for diffusing the error data are displaced left and right on the same line, thereby making the diffusion sites different. The diffusion site is changed continuously for each line. The error data is spread so that the amount of change and the change order of the diffusion sites are aperiodic in the line direction and the field direction. Details of the method of spreading the aperiodic error data will be described later.

Preferably, the error data is not cleared (reset) to zero outside the effective video period, that is, in the horizontal blanking period or the vertical blanking period. Specifically, when transitioning from the valid video period to the valid video period outside of the video signal, error data is generated without clearing the lower 4 bits obtained from the pixel of interest immediately before reaching the valid video period to zero. Normally, the pixel of interest immediately before reaching the effective video period is a pixel located at the uppermost line of the effective video period of the video signal and at the left end of each line, but is not limited thereto.

Not clearing to zero means keeping the lower 4 bits obtained from the pixel of interest immediately before reaching the effective video period, or substituting a random value as a value corresponding to the lower 4 bits. In this process, light emission due to error diffusion occurs at regular intervals, and the light emission results in a state having two values: a dot that emits light every time and a dot that does not emit light every time, resulting in a bit line image or a granular still image of a vertical line or an oblique line. This is to prevent interference in image quality.

In addition, the process of changing the diffusion location or in addition to not clearing the error data to zero outside the effective video period is performed on at least one signal (dot) among the pixels of interest composed of dots of the R, G, and B signals. . It is preferable to perform the above process for two signals (dots) among the R, G, and B signals, and more preferably to perform the above process for all the signals (dots) of the R, G, and B signals.

In this embodiment, as a more preferable example, in addition to the change in the diffusion location, the error diffusion coefficient for at least one signal is not used for other signals, instead of using a common error diffusion coefficient for the R, G, and B signals. The number of bits used for error diffusion for at least one signal, that is, the number of bits spread in the upper 8 bits, is different from the number of bits used for error diffusion for another signal.

In addition, the R, G, and B signals which have been error-diffused by the error diffusion processing circuits 3R, 3G, and 3B in FIG. 1 are input to the PDP 4. The PDP 4 displays R, G, and B images on the screen after performing various driving processes such as subfield processing. The PDP 4 here includes a panel and its driving portion.

Hereinafter, the specific structure of the error diffusion processing circuit 3 is demonstrated using FIG. The R error diffusion processing circuit 3R, the G error diffusion processing circuit 3G, and the B error diffusion processing circuit 3B all have the same configuration, but the R error diffusion processing circuit 3R and G error diffusion processing In at least one of the circuit 3G and the error diffusion processing circuit 3B for B, the dot to be diffused is error-displaced. In addition, the error diffusion coefficient and the number of bits used for error diffusion are different. The configurations of the G error diffusion processing circuit 3G and the B error diffusion processing circuit 3B are common to the R error diffusion processing circuit 3R, which simplifies the illustration and omits the description of the operation. do.

In Fig. 2, the 12-bit R signal input from the inverse gamma correction circuit 2 is output via the adders 31 and 32 described later, and the lower 4 bits of the 12 bit data output from the adder 32 are shown. Is input to the R error detection circuit 33R. The lower four bits correspond to the difference of the damaged gradation by reducing the 12-bit digital signal (4096 gradation) to the 8-bit digital signal (256 gradation). The error detection circuit 33R for R multiplies the error data by the error diffusion coefficients according to the peripheral dots A 'to D' shown in FIG. 3 (A) or 4 (A) with respect to the input lower 4 bits of data. It happens.

From the terminals a to d of the R error detection circuit 33R, error data obtained by multiplying the lower 4 bits of data by the error diffusion coefficient according to the peripheral dots A 'to D' is output. In the case of Fig. 3A or Fig. 4A, the error data obtained by multiplying the data of the lower 4 bits by 7/16, 3/16, 5/16, and 1/16 from the terminals a to d, respectively. Is output. The relationship between the peripheral dots A'-D 'and the peripheral dots A-D is mentioned later.

The error data output from the terminal a is input to the adder 32, the error data output from the terminal b is input to the adder 35, and the error data output from the terminals c and d are input to the adder 34. The adder 34 adds the error data from the input terminals c and d and inputs it to the adder 35. The adder 35 adds the error data output from the terminal b and the output of the adder 34 and inputs it to the line memory 36.

The random number generator 38 inputs a horizontal synchronous signal, a vertical synchronous signal, and a displacement setting value. The displacement amount setting value is used when the error data is diffused to a pixel located at a line behind the pixel of interest, and the error data is diffused several pixels from the reference position to the left and right directions from the reference position. The value which displaces a pixel (at least one dot). This displacement amount setting value may be a predetermined fixed value. As the setting method of the displacement amount setting value, the displacement amount may not necessarily be left-right symmetrical, for example, may be set within the range of 3 pixels in the right direction and 4 pixels in the left direction. Since the amount of displacement is not too large and a few pixels is used to reduce noise, it is preferable to set it to less than 10 pixels in one direction.

The random number generated by the random number generator 38 is generated for each line within the range of the displacement amount setting value. In the above example, a random number selected from three types of 1 to 3 pixels in the right direction, 4 types of 1 to 4 pixels in the left direction, and 8 types of normal processing (0 pixels) which do not move in the left and right directions, Occurs randomly (including substantially random) per line. The random number value is generated while controlling such that the order of appearance before and after, i.e., the order of appearance in the up-down direction and the appearance in the field (or frame) direction is aperiodic. An example of aperiodic change in the displacement amount will be described later. Further, it is better to change the displacement amount by varying the displacement amount setting value at the timing of the vertical synchronization signal.

The timing of the read side reset signal 38A and the write side reset signal 38B is set for each line and output from the random number generator 38 based on the value of the input random number and the timing of the horizontal synchronization signal. The read side reset signal 38A and the write side reset signal 38B output from the random number generator 38 are input to the line memory 36. The line memory 36 delays the output of the adder 35 by a time slightly shorter than one line based on the timing of the read side reset signal 38A and the write side reset signal 38B. 31). Details of the above operation will be described later.

By the way, it is common to clear (reset) the error data recorded in the line memory 36 to 0 outside the effective video period. In contrast, in the present embodiment, the line memory 36 is not cleared to zero outside the effective video period, that is, in the horizontal blanking period or the vertical blanking period. As a result, as described above, when the transition from the valid video period to the valid video period is performed, error data is generated without clearing the lower 4 bits obtained from the pixel of interest immediately before reaching the valid video period to zero. .

The adder 31 adds the input R signal and the output of the line memory 36 and inputs it to the adder 32. When the input R signal is set as the attention dot P 'shown in FIG. 3 (A) or FIG. 4 (A), the adder 31 has the error which occurred in the past about 1 line with respect to the attention dot P'. The operation of adding the output of the line memory 36 as data, that is, B'x3 / 16 + C'x5 / 16 + D'x1 / 16 is executed.

The adder 32 adds the output of the adder 31 and the error data output from the terminal a of the R error detection circuit 33R. That is, the adder 32 selects A '× 7/16, which is error data generated in the past one dot, with respect to the output of the adder 31 which adds the error data generated in the past about one line with respect to the dot P' of interest. The addition operation is performed. Thus, the error data obtained by multiplying the dot D 'of interest shown in Fig. 3A or Fig. 4A by the respective error diffusion coefficients to the peripheral dots A' to D 'is added. Of the 12 bits of data output from the adder 32, the lower 4 bits are again input to the R error detection circuit 33R, and the above operation is repeated.

The upper 8 bits of the 12 bits of data output from the adder 32 are input to the limiter 37. The limiter 37 outputs the limit (overflow) exceeding 8 bits of the value of the data obtained by the addition process of the error data for the dot P 'of interest.

As described above, the addition process of the error data for the dot P 'of interest is performed sequentially for each dot, as a result of the lower 4 bits of the dot P of interest as shown in FIG. 3 (A) or FIG. 4 (A). This means that the data is multiplied by error diffusion coefficients of 7/16, 3/16, 5/16, and 1/16 to diffuse into the surrounding dots A to D. FIG.

In the example shown in FIG. 2, the error diffusion coefficient set in the G error detection circuit 33G in the G error diffusion processing circuit 3G is the same as the error diffusion coefficient set in the R error detection circuit 33R. The error diffusion coefficient set in the B error detection circuit 33B in the B error diffusion processing circuit 3B or the number of bits used for error diffusion is used for the R error detection circuit 33R and the G error detection circuit 33G. It is different from the error diffusion coefficient set in the above and the number of bits used for error diffusion.

Fig. 3 shows a case in which the error diffusion coefficients are different, and as shown in Fig. 3B, for the B signal, 9/16, 2/16, 4 is applied to the data for the lower 4 bits in the dot P of interest. Multiply the error diffusion coefficients by / 16, 1/16 so that the surrounding dots A to D are spread.

In this way, the error diffusion processing circuits 3R, 3G, and 3B are used for one signal or all signals in the R, G, and B signals in the pixel of interest composed of three dots of the R, G, and B signals. By performing error diffusion processing on the R, G, and B signals with different error diffusion coefficients, 12 bits of data are output as 8 bits of data. In addition, all of the error diffusion coefficients with respect to the surrounding dots A-D may differ, and only a part may differ. In the example of FIG. 3, the error diffusion coefficient for the peripheral dots D is common to 1/16, and the error diffusion coefficients for the other peripheral dots A to C are different. The error diffusion coefficient should be slightly different rather than greatly different.

Even in the PDP 4 having only 8-bit display capability as described above, by using the visual integration effect, it is possible to display an image that can be recognized as a display image equivalent to 12 bits in appearance. In addition, a diffusion error to a pixel located at least one line or more behind the pixel of interest without using a common error diffusion coefficient as an error diffusion coefficient for the R, G, and B signals is determined by the R, G, and B signals. Since at least one signal is continuously changed randomly from line to line, even when displaying a fixed pattern or the like, image quality disturbances such as periodic pattern noise characteristic of error diffusion, such as error diffusion represented by granularity or bit shape, are very visually significant. It is hard to be recognized. Therefore, a higher quality display device can be provided.

Fig. 4 shows a case where the number of bits used for error diffusion is different. As shown in Fig. 4B, for the B signal, the 3 bits from the lower 4 bits to the lower 2 bits in the dot P of interest are shown. The data is multiplied by the error diffusion coefficients of 4/8, 1/8, 2/8, and 1/8 to diffuse into the surrounding dots A to D.

In the present embodiment, error diffusion is performed using 3 bits from the lower 4 bits to the lower 2 bits in the B signal of 12 bits, but the inverse gamma in the inverse gamma correction circuit 2 is applied to the B signal. In the step of the correction process, an 11-bit digital signal, i.e., a 2048 gray level signal, is output with the same inverse gamma correction characteristic as that of the R and G signals, and the lower 3 bits of the data are multiplied by the error diffusion coefficient to obtain a peripheral dot You may diffuse to A-D.

In this case, when the inverse gamma correction process of the B signal is realized by the lookup table (LUT) using the ROM (ROM), the ROM capacity is saved by that amount. In addition, when the inverse gamma correction process is 11 bits, since the processing executed by the error diffusion circuit 3B for B all ends in the processing circuit for 3 bits, the circuit capacity is saved. There is also an effect that the delay of approximately one line in the line memory 36 is also at least one bit.

In this way, the error diffusion processing circuits 3R, 3G, and 3B are used for one or all signals in the R, G, and B signals in the pixel of interest composed of three dots of the R, G, and B signals. By varying the number of bits used for error diffusion, the error diffusion processing is performed on the R, G, and B signals, thereby outputting 12 bits of data (11 bits of the B signal) as 8 bits of data. In addition, the number of bits used for error diffusion may be slightly different from that of greatly different.

Even in the PDP 4 having only 8-bit display capability as described above, by using the visual integration effect, an image that can be recognized as a display image of 12 bits equivalent (11 bits equivalent) is apparently displayed. Can be. In addition, at least one signal of the R, G, and B signals may be diffused to a pixel located one or more lines behind the pixel of interest without having the same number of bits used for error diffusion for the R, G, and B signals. Since each row line is randomly changed continuously, even when displaying a fixed pattern or the like, image quality disturbances such as periodic pattern noises unique to error diffusion represented by, for example, granularity or bit shape, are hardly recognized visually. Therefore, it becomes possible to provide a higher quality display device.

In the present embodiment, the number of bits used for error diffusion of the B signal is 3 bits, and the number of bits used for error diffusion of the R and G signals is 4 bits, but the number of bits used for error diffusion is 3 bits or 4 bits. It is not limited. When not all of the lower bits of the first number of bits, which is the difference between the first number of bits and the second number of bits, are used for error diffusion, but a part of the lower bits is used for error diffusion. Consecutive higher bits from the most significant bit of (in the above example, the lower fourth bit) are used.

In this embodiment, the number of bits used for the error diffusion of the R and G signals is set to 4 bits, and the error diffusion coefficients of the respective peripheral dots are the same, but the error diffusion coefficients of the peripheral dots may be different.

As an example, for the R signal, as shown in Fig. 5A, 7/16, 3/16, 5/16. The error diffusion coefficient of 1/16 is multiplied so as to spread to the surrounding dots A to D. As for the G signal, as shown in FIG. 5 (B), 9/16, Multiply the error diffusion coefficients 2/16, 4/16, and 1/16 to spread to the surrounding dots A to D. For the B signal, as shown in FIG. Error diffusion coefficient of 4/8, 1/8, 2/8, 1/8 to 3 bits of data to the lower 2 bits (or lower 3 bits of data if reverse gamma correction processing is 11 bits) It may be multiplied by so as to diffuse into the surrounding dots A to D.

In this way, the error diffusion processing circuits 3R, 3G, and 3B are used for the one pixel or all the signals in the R, G, and B signals in the pixel of interest composed of three dots of the R, G, and B signals. By varying the error diffusion coefficient or by varying the number of bits used for error diffusion of one signal or all signals in the R, G, and B signals, the error diffusion process is performed on the R, G, and B signals, thereby performing 12 bits. Alternatively, 11 bits of data are output as 8 bits of data.

Next, a description will be given of a method of changing the diffusion place to the pixel dot located in the line behind the pixel of interest with respect to at least one signal of the R, G, and B signals for each line. In this embodiment, a more preferred embodiment will be described in which the diffusion location is different for each of the R, G, and B signals. FIG. 6 shows an example of a case where the diffusion location of a pixel located at least one line behind the pixel of interest is changed for each of the R, G, and B signals, and FIG. 7 is a view of the pixel present at least one line behind the pixel of interest. An example of the case where the diffusion point to a dot is changed for each line is shown.

First, FIG. 6 will be described. Dots of interest P shown in FIGS. 6A, 6B, and 6C are pixels located at the same place and are three dots constituting the pixel of interest. Each error diffusion coefficient diffused to A, B, C, and D shown in FIG. 6 is the same as each error diffusion coefficient diffused to dots A, B, C, and D shown in FIGS. . In FIG. 6, description of the value itself of each error diffusion coefficient spreading to dots A, B, C, and D is omitted.

As for the R signal in Fig. 6A, the dot A on the right side in the dot P of interest, the dot B immediately below, the dot C on the lower right side, and the dot D on the lower right side of two pixels are diffused. In the G signal of Fig. 6B, the dot A on the right side in the dot P of interest, the dot B on the lower left side, the dot C immediately below, and the dot D on the lower right side are diffused. In the signal B of FIG. 6C, the dot A on the right side in the dot P of interest, the dot B on the lower left of the two pixels, the dot C on the lower left, and the dot D immediately below are spread. In this way, the diffusion sites of the pixels located one or more lines behind the pixel of interest (here, the pixels located one line behind) into dots are different for each of the R, G, and B signals.

The R error diffusion processing circuit 3R, G error diffusion processing circuit 3G, and B error diffusion processing circuit 3B shown in FIG. 2 have the same circuit configuration, but R as shown in FIG. The change of the spreading area for each of the G and B signals can be easily realized by shifting the read start position of the read side reset signal of each line memory 36 for each of the R, G and B signals. If the change in the diffusion location is realized by shifting the read start position of the line memory 36, as shown in Fig. 6, the relative positional relationship (the distance between the dots or the respective dots) of the dots B, C, and D is changed. It doesn't work.

This invention is not limited to this, You may make it shift the relative positional relationship of dots B, C, and D, or place dots B, C, and D in another line in the same line. For example, the R signal may be spread below one line of the dot P of interest, the G signal may be spread below two lines of the dot P of interest, and the B signal may be spread below three lines of the dot P of interest. Further, for example, the dot A may also be included in each field to change the relative positions of the dots B, C, and D with respect to the pixel P of interest. Alternatively, the start position of the recording side reset signal of the line memory 36 may be shifted or both of the recording side reset signal and the read side reset signal may be shifted.

Next, FIG. 7 is demonstrated. 7, the first to fifth lines in FIG. Indicates a display line of the PDP 4. It is assumed that the dot P of interest is at the position shown in FIG. 7 of the first line. The dot of interest P is one of the signals of R, G, and B, and it is assumed that the dot N is a signal of the same color as the dot of interest P from the dot B shown after the second line.

From the dot P of interest in the first line, error data is diffused into dot A on the right side, dot B on the right side, dot C on the bottom right, and dot D on the right side of two pixels. The spreading position of the error data to the peripheral pixels in the first line is the same as the noticeable dot P shown in the drawing, with the right side dot A, the right dot B, the right bottom C C, and the right of 2 pixels. The following dots are diffused as D. The error diffusion coefficients diffused into dots A, B, C, and D shown in FIG. 7 are the same as the error diffusion coefficients diffused into dots A, B, C, and D shown in FIGS. Just do it. In FIG. 7, the description of the value itself of each error diffusion coefficient diffused to dots A, B, C, and D is omitted.

Next, dot B is the attention dot in the second line, dot F is the attention dot in the third line, and dot J is the attention dot in the fourth line. From the spot dot B of the 2nd line, it spreads to the dot C of the right side, the dot E of the lower left, the dot F of the right underneath, and the dot G of the lower right. The values of the error diffusion coefficients diffused to the right side dot C, the bottom left dot E, the right bottom dot F, and the right bottom dot G are the dots A, B, C, It is equal to each error diffusion coefficient in D.

From the dot F of attention of the 3rd line, it spreads to the dot G of the right side, the dot H of the lower left of 2 pixels, the dot I of the lower left, and the dot J immediately below. The values of the error diffusion coefficients diffused to the right side dot G, the two pixels left lower dot H, the lower left dot I, and the dot J immediately below are the dots A, B, It is equal to the error diffusion coefficient of C and D. From the dot J of the 4th line, it spreads to the dot K of the right side, the dot L just below, the dot M of the lower right, and the dot N of 2 pixels lower right. The values of the error diffusion coefficients that are diffused into the right side dot K, the right bottom dot L, the right bottom dot M, and the right bottom dot N, the two pixels right dot N are the dots A, B, It is equal to the error diffusion coefficient of C and D respectively.

The R error diffusion processing circuit 3R, G error diffusion processing circuit 3G, and B error diffusion processing circuit 3B shown in FIG. 2 have the same circuit configuration, but are each line as shown in FIG. The change of the diffusion point can be easily realized by shifting the read start position of the read side reset signal of each line memory 36 from line to line, for example. When the diffusion point is changed by shifting the read start position of the line memory 36, attention dots P, B, F, J,... The relative positional relationship (the sequence or the distance between each dot) of the dots located one line behind is not changed.

The present invention is not limited to this, but shifts the relative positional relationship of each of the three dots located behind one line in the same line, or switches the position of the rear line diffused for each line, so that the three dots are different from each other. It may be located at. For example, it spreads down one line from the attention dot P of a 1st line, spreads below 2 lines from the attention dot B of a 2nd line, and 3 lines from the attention dot F of a 3rd line. The distance to be diffused downward or the distance to be diffused in the line direction may be different. Further, for example, a dot (dot A in the first line) located in the same line as the pixel of interest for each field or frame may also be included to change the relative position with respect to the pixel of interest.

Alternatively, the start position of the recording side reset signal of the line memory 36 may be shifted or both of the recording side reset signal and the read side reset signal may be shifted.

FIG. 8 is a timing chart showing an example in which the change of the diffusion place shown in FIG. 7 is shifted between both the write side reset signal and the read side reset signal of the line memory 36. As shown in Figs. 8A to 8E, the amount of delay between the read side reset and the write side reset based on the position of the read side reset of the first line (the read side reset corresponds to one line). After the constant is set at a slightly shorter time, the change of the diffusion location is realized by simultaneously shifting both reset signal starting positions after the second line to the positive side and the negative side.

In the example of FIG. 2, the change of the diffused place as shown in FIG. 8 is realized by using the random number generator 38, but the means for changing the diffused place is not limited to the random number generator. For example, it may be a generation circuit using the M series. The specific means of changing the diffusion site is arbitrary.

Here, with reference to FIG. 9, the specific example of the spreading method of aperiodic error data is demonstrated. In Fig. 9, the longitudinal direction represents a line number, and the lateral direction represents a field (or frame) number. As the video signal supplied to the display device of FIG. 1, there may be a case of an interlaced signal and a case of a non-interlaced signal depending on the driving mode of the PDP 4. In the example of FIG. 9, as described above, the displacement amount of the pixel diffusing the error data is three pixels in the right direction, four pixels in the left direction, and eight cases including zero pixels not displaced. It is shown. In FIG. 9, the left direction is shown as + (plus) and the right direction as-(minus). In addition, the example of FIG. 9 does not show the same state as FIG.

As shown in Fig. 9, in field (frame) 1, the displacement amount of line 1 which is the top line of the effective video period of the video signal is +4, the displacement amount of the subsequent line 2 is +3, and the displacement amount of the next line 3 is -3. It is 2. Thus, in this embodiment, the displacement amount of the pixel which spreads the error data is sequentially changed within the range of the displacement amount setting value for each line. When the number of lines in the effective video period is 480, it is preferable to set the displacement amount randomly in all the 480 lines. However, for the sake of simplicity of the circuit or software, the present embodiment is as follows.

That is, the eight lines of the lines 1-8 shown in FIG. 9 are made into one area | region, and the displacement amount is selected aperiodically in this one area | region. In this example, the same displacement amount does not appear in one region. Although illustration is abbreviate | omitted, also in the line 9-16 which is the next one area | region, it is set as the displacement amount similar to the lines 1-8. In this way, although it is periodical when it sees between several area | regions, it is substantially random aperiodically in one area | region.

For example, in line 1, the displacement amount of the field (frame) 1 is +4, the displacement amount of the next field (frame) 2 is +2, and the displacement amount of the next field (frame) 3 is -3. Thus, in this embodiment, the displacement amount of the pixel which spreads the error data is sequentially changed within the range of the displacement amount setting value for each screen of the field or frame. Although it is preferable to always set the displacement amount randomly in the field (frame) direction, for the sake of simplicity of the circuit or software, this embodiment is as follows.

That is, eight fields (frames) of the fields (frames) 1 to 8 shown in FIG. 9 are set as one time region, and the displacement amount is selected aperiodically in this one time region. The area surrounded by the thick solid line is one time region. In this example, the same displacement amount does not appear in one time domain. Although not shown, the same amount of displacement as those of the fields (frames) 1 to 8 is also used for the fields (frames) 9 to 16, which are the next one time areas. In this way, although viewed between a plurality of time domains, it is periodic, but aperiodic substantially random in one time domain.

Also in this embodiment, it is effective effectively in preventing the image quality disturbance which becomes a bit-shaped image and a granular still image of a vertical line or an oblique line.

As described in detail above, according to the error diffusion processing method of the display device of the present invention, image disturbance such as periodic pattern noise that appears when error diffusion processing is performed on an image having a large area of an extremely dark low gradation part exists. Can be reduced very effectively. In addition, even if the panel becomes higher in brightness and the luminance step difference in the low gradation portion is increased, the emission probability (light emission count) of each dot is more averaged in a predetermined area, so even if there are many images near the low gradation, noise due to error diffusion A feeling of a sense is not felt, and deterioration of the image quality by high brightness of a panel can be suppressed as much as possible.

Claims (2)

The first bit in each pixel of interest composed of a plurality of dots forming a color component when the video signal having the first number of bits is reduced to the second number of bits having a smaller number of bits than the first number of bits; A pixel located in a line behind the line where the pixel of interest is located, the error data obtained by multiplying a predetermined error diffusion coefficient by at least a part of the lower bit of the first bit number, which is a difference between the number and the second bit number; In the error diffusion processing method of the display device to diffuse to the points of the plurality of peripheral pixels, When at least a part of a plurality of lines in the effective video period of the video signal is set as one region, the position in the line direction of the pixel of interest in the one region is set as the reference position and is located at the rear line for diffusing the error data. By shifting the position of at least one point of the pixel to shift the read start position of the memory holding the error data, aperiodically shifts for each line within the range of the preset number of pixels in the left and right directions from the reference position, When the one area over a plurality of screens, which are a plurality of fields or a plurality of frames, is set as one time area, the position of at least one point of a pixel that diffuses the error data in each line in the one time area is determined. And shifting the reading start position of the memory holding the error data non-periodically for each screen within the range of the preset number of pixels in the left and right directions from the reference position. The method of claim 1, When shifting from the effective video period to the effective video period of the video signal, the error data is generated without setting the lower bits of the first number of bits obtained from the pixel of interest immediately before reaching the valid video period to zero. Error diffusion processing method of the display device.

Images