JP4172331B2 - Error diffusion processing method for display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an error diffusion processing method used for 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), and the like. As described above, in a display device that expresses digitally limited intermediate gradations, the present invention relates to an error diffusion processing method for a display device that can reduce image quality interference caused by multi-gradation processing by error diffusion processing. .
[0002]
[Prior art]
Among display devices that display video signals, for example, a PDP that displays gradation by dividing one field into a plurality of subfields, an FED that displays gradation by pulse width modulation (PWM), and a matrix type such as DMD In a display device, an image can be expressed only with a digitally limited number of gradations depending on the driving method.
[0003]
Normally, in television broadcasting and the like where the receiver is assumed to be a cathode ray tube (CRT), a gamma characteristic is given in advance on the transmitter side, and a linear scale is combined with the inverse gamma characteristic of the CRT on the receiver side. It is designed to have a tonal characteristic. However, in the display device as described above that displays an image with a digitally limited number of gradations, unlike the CRT, the display device itself has linear gradation characteristics. Therefore, in order to display an image with the same gradation characteristics as a display device using CRT that is usually used, the input image signal of the display device is subjected to a 2.2 power inverse gamma correction process to return to the linear gradation characteristics. It is necessary to display an image.
[0004]
On the other hand, in these display devices, the number of gradations (bit number) of the input signal may be larger than the number of gradations (bit number) that can be expressed by the display device. In some cases, the number of gradations (number of bits) expressed by the display device is intentionally reduced from the number of gradations (bits) of the input signal.
[0005]
Further, when the inverse gamma correction circuit performs the inverse gamma correction processing to return to the linear gradation, the number of bits may be temporarily increased from the number of bits that can be expressed by the display device. This is due to the following reason. When the inverse gamma correction process is performed to return to a linear gradation, the number of gradations at a low luminance level is impaired, and image quality interference often resulting from the loss of gradation continuity may occur. In particular, in the case of PDP, one field is composed of a plurality of subfields having different light emission weights, and gradation is expressed by selecting a plurality of subfields.
[0006]
Therefore, depending on the selection condition of the subfield, the visual luminance difference with respect to the adjacent gradation becomes large, and as a result, the pseudo-contour image quality interference may occur. Therefore, in order to prevent the gradation from being lost as much as possible, the inverse gamma correction processing is performed with the number of bits higher than the number of bits of the original signal, and the number of bits is increased and output.
[0007]
As described above, the number of bits of the input video signal or the number of gradations (first bit number) of the video signal output from the inverse gamma correction circuit is the number of gradations (second bit number) expressed by the display device. If it is greater than (), it is necessary to reduce the number of gradations (number of bits). If the number of gradations (number of bits) is reduced, gradations are impaired, and therefore, multi-gradation processing is performed using an error diffusion method.
[0008]
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 the three dots constituting the pixel of interest, and is a dot having a gradation number that cannot be expressed as it is with the second number of bits. A is a dot on the right, B is a lower left dot, C is a lower dot, and D is a lower right dot. As shown in FIG. 10, the first number of bits that cannot be expressed in the target dot P−the second number of bits is diffused with a certain weight applied to the plurality of peripheral dots A to D. It is a common method to perform multi-gradation processing so that an image corresponding to the first number of bits is obtained.
[0009]
For example, when the display device has only 8-bit gradation capability and gradation display is performed with the upper 8 bits of the 12-bit dot data, the dot data for the remaining lower 4 bits is given a certain weight, and the peripheral dots By diffusing to A to D, a gradation display equivalent to 12 bits is performed using a 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 that indicate the degree of weighting. A common error diffusion coefficient is used for the three primary color signals of R, G, and B.
[0010]
As a conventional error diffusion processing method for a display device, there is a prior application by the present applicant, described in Japanese Patent Application Laid-Open No. 2002-135608 (Patent Document 1). In the invention described in Patent Document 1, the diffusion location of error data to pixels located one or more lines behind the target pixel is changed with respect to at least one of the R, G, B signals, By changing it every time, the occurrence probability of image quality interference such as periodic pattern noise appearing when error diffusion processing is performed is drastically reduced, and high-quality display is realized.
[0011]
[Patent Document 1]
JP 2002-135608 A
[0012]
[Problems to be solved by the invention]
In the case of a display device as described above, particularly in the case of a PDP, by performing the multi-gradation processing by the error diffusion method as described above, the number of apparent gradations is increased and the image quality of the pseudo contour shape is increased. I try to reduce interference. However, in the past, the number of bits used for error diffusion for the three primary color signals of R, G, and B is set to a common bit number and a common error diffusion coefficient is used. When displaying a fixed pattern or the like, there is a problem that image quality interference such as periodic pattern noise peculiar to error diffusion may occur.
[0013]
Furthermore, the performance of display devices such as PDPs has been continuously improved by improving the structure of the panel and the materials constituting the inside of the panel, and the brightness of the panel has been increasing. For this reason, image quality interference such as periodic pattern noise peculiar to the above error diffusion tends to become more conspicuous. In particular, it has been clarified that an image having many low gradation portions has a problem that the image quality is further deteriorated as the brightness of the panel is increased.
[0014]
Although the invention described in Patent Document 1 can largely solve these problems, it has become clear that the following new problems exist. Even if the diffusion location of the error data is changed for each of R, G, B and each line, in the invention described in Patent Document 1, the change of the diffusion location is regular, and the light emission probability of each dot with respect to a certain display area ( The number of times of light emission becomes imbalanced. As a result, the difference in shading between the dots that emit much light and the dots that emit little light is clear, and the visual luminance difference between adjacent dots increases. Then, in an image having a large area of a low gradation part in a very dark part, the S / N in the dark part is poor and a sense of noise is felt a lot.
[0015]
In addition, in the case of a still image in which a very small level of video signal near black is uniformly present on the entire screen, depending on the signal level, light emission due to error diffusion occurs at regular intervals. This results in a binary state with dots that do not occur, causing image quality interference that becomes a beat-like image of vertical lines or diagonal lines, or a granular still image. In the case of a two-dimensional image such as a printed matter, there is no problem even if it becomes a granular still image. However, in the case of a display device that handles a three-dimensional image, particularly in the case of a television application, if it becomes a granular still image, the conventional CRT display This is not preferable because the device feels uncomfortable.
[0016]
The present invention has been made in view of such problems, such as periodic pattern noise that appears when error diffusion processing is performed on an image having a large area of a low-gradation portion in a very dark portion. It is an object of the present invention to provide an error diffusion processing method for a display device that can extremely effectively reduce image quality interference.
[0017]
[Means for Solving the Problems]
In order to solve the above-described problems of the prior art, the present invention reduces the color of a video signal having a first number of bits to a second number of bits that is smaller than the first number of bits. A predetermined number of low-order 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 composed of a plurality of dots forming a component In the error diffusion processing method of a display device, in which error data multiplied by an error diffusion coefficient is diffused to a plurality of peripheral pixels including a plurality of pixels located on a line behind the line on which the pixel of interest is located. When at least a part of a plurality of lines in the video period is defined as one area, the position of the target dot, which is the color component in the target pixel, in the line direction is set as a reference position in the one area, and the error data is set. The diffusion positions of a plurality of dots located at the rear of the line to spread the data, non-periodically displaced for each line within the number of dots set in advance in the left-right direction from the reference position ,And The diffusion position of the error data from the same reference position in the line direction in two adjacent lines is prevented from being the same, and the one area across a plurality of screens that are a plurality of fields or a plurality of frames is set for one hour. When the area is set, the diffusion position of a plurality of dots located in the rear line for diffusing the error data in each line in this one-hour area is a range of the number of dots set in advance in the horizontal direction from the reference position. Within a non-periodic displacement for each screen ,And An error diffusion processing method for a display device, characterized in that the diffusion position of the error data from the same reference position in the line direction on the same line of two adjacent screens is not the same is provided. .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an error diffusion processing method for a display device of the present invention will be described with reference to the accompanying drawings. 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 an error diffusion processing circuit 3 in FIG. 1, and FIGS. 6 is a diagram for explaining a preferred example of the error diffusion processing method of the present invention, and FIGS. 7 to 9 are diagrams for explaining the error diffusion processing method of the present invention.
[0019]
In the present embodiment shown in FIG. 1, a case is shown in which a PDP is used as a matrix type display device that can express an image only with a digitally limited number of gradations. Of course, the display device of the present invention is not limited to the PDP. In FIG. 1, three systems of video signals composed of R, G, and B signals that are color components are input to a video signal processing circuit 1. The video signal processing circuit 1 performs various types of video signal processing on these video signals and inputs them to the inverse gamma correction circuit 2. For example, the R, G, and B signals are 8-bit digital signals, that is, signals having 256 gradations.
[0020]
The inverse gamma correction circuit 2 performs reverse gamma correction processing with the same characteristics on the input R, G, and B signals, and outputs a 12-bit digital signal, that is, a signal of 4096 gradations as an example. The reason why the 8-bit digital signal is output as the 12-bit digital signal is to prevent the number of gradations from being damaged by the inverse gamma correction processing as described above.
[0021]
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 includes an R error diffusion processing circuit 3R, a G error diffusion processing circuit 3G, and a B error diffusion processing circuit 3B, and the R, G, and B signals are respectively error diffusion processing circuits 3R, 3G. , 3B. The error diffusion processing circuits 3R, 3G, and 3B perform error diffusion processing on the input R, G, and B signals and output the signals. That is, error data in which, for example, the lower 4 bits of the 12-bit digital signal are weighted with a certain weight is diffused into the upper 8 bits and output as an 8-bit digital signal.
[0022]
At this time, when the error data is diffused to the dots of the pixels located in the line behind the line where the pixel of interest is located (at least one line behind), as in the pixels B, C, and D in FIG. Is not constant, but the pixels for diffusing the error data are displaced in the left-right direction on the same line, and the diffusion locations are made different. This diffusion location is continuously changed for each line. The error data is diffused so that the change amount and change order of the diffusion location are aperiodic in the line direction and the field direction. Details of the non-periodic error data diffusion method will be described later.
[0023]
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. More specifically, when the video signal shifts from outside the effective video period to the effective video period, error data is generated without clearing the lower 4 bits obtained at the pixel of interest immediately before the effective video period to zero. To do. Normally, the target pixel 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 the left end of each line, but is not limited to this depending on the driving method.
[0024]
Not clearing to zero means that the lower 4 bits obtained at the pixel of interest immediately before the effective video period are held, or that a random value is substituted as a value corresponding to the lower 4 bits. In this process, light emission due to error diffusion occurs at regular intervals, resulting in a binary state of dots that emit light each time and dots that do not emit light each time, resulting in a beat-like image or a granular still image with vertical lines or diagonal lines. This is to prevent image quality interference.
[0025]
In addition, the process of changing the diffusion location and additionally not clearing the error data to zero outside the effective video period is performed using at least one signal (dot) of the pixel of interest composed of dots of the R, G, and B signals. ) It is preferable to perform the above processing on two signals (dots) of the R, G, B signals, and to perform the above processing on all signals (dots) of the R, G, B signals. Further preferred.
[0026]
In the present embodiment, as a more preferable example, in addition to changing the diffusion location, the common error diffusion coefficient is not used for the R, G, B signals, but the error diffusion coefficient for at least one signal is used as another signal. Or the number of bits used for error diffusion for at least one signal, that is, the number of bits diffused into the upper 8 bits is different from the number of bits used for error diffusion for other signals.
[0027]
In FIG. 1, the R, G, and B signals subjected to the error diffusion processing by the error diffusion processing circuits 3R, 3G, and 3B are input to the PDP 4. The PDP 4 displays various R, G, and B signals on the screen after performing various drive processes such as a subfield process. Here, the PDP 4 includes a panel and its driving unit.
[0028]
Here, a specific configuration of the error diffusion processing circuit 3 will be described with reference to FIG. The R error diffusion processing circuit 3R, the G error diffusion processing circuit 3G, and the B error diffusion processing circuit 3B have the same configuration, but the R error diffusion processing circuit 3R and the G error diffusion processing circuit 3G, B In at least one of the error diffusion processing circuits 3B for use, a dot to be subjected to error data diffusion is displaced. In addition to this, the error diffusion coefficient and the number of bits used for error diffusion are varied. The configuration of the G error diffusion processing circuit 3G and the B error diffusion processing circuit 3B is the same as that of the R error diffusion processing circuit 3R, so that the illustration is simplified and the description of the operation is omitted.
[0029]
In FIG. 2, the 12-bit R signal input from the inverse gamma correction circuit 2 is output through adders 31 and 32, which will be described later. Of the 12-bit data output from the adder 32, the lower 4 bits are This is input to the R error detection circuit 33R. The lower 4 bits correspond to the gradation difference lost by reducing the 12-bit digital signal (4096 gradations) to the 8-bit digital signal (256 gradations). The R error detection circuit 33R multiplies the input lower 4 bits of data by error diffusion coefficients corresponding to the peripheral dots A ′ to D ′ shown in FIG. 3A or FIG. Is generated.
[0030]
From the terminals a to d shown in the R error detection circuit 33R, error data obtained by multiplying the lower 4 bits of data by an error diffusion coefficient corresponding to the peripheral dots A 'to D' is output. In the case of FIG. 3A or FIG. 4A, the lower 4 bits of data are multiplied by 7/16, 3/16, 5/16, 1/16 from the terminals a to d, respectively. Error data is output. The relationship between the peripheral dots A ′ to D ′ and the peripheral dots A to D will be described later.
[0031]
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 is input to the adder 34. . The adder 34 adds the error data from the input terminals c and d and inputs the added error data 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 the result to the line memory 36.
[0032]
The random number generator 38 receives a horizontal synchronization signal, a vertical synchronization signal, and a displacement set value. The displacement set value means that when error data is diffused to the pixels located in the line behind the target pixel, the position of the target pixel in the line direction is used as the reference position, and the error data for the number of pixels in the horizontal direction from the reference position. The value is whether the pixel (at least one dot) to be diffused is displaced. The displacement amount setting value may be a predetermined fixed value. As a setting method of the displacement amount setting value, the displacement amount does not necessarily have to be bilaterally symmetric. For example, the displacement amount may be set within a range of 3 pixels in the right direction and 4 pixels in the left direction. The amount of displacement is not so large, and a noise feeling can be reduced by setting it to about several pixels. Therefore, it is preferable that the amount of displacement be less than 10 pixels in one direction.
[0033]
The random number generated by the random number generator 38 is generated for each line within the range of the displacement set value. In the above example, three types of 1 to 3 pixels in the right direction, four types of 1 to 4 pixels in the left direction, and normal processing that does not move in the left and right direction (0 pixels) are selected from a total of 8 types. A random number is randomly generated for each line (substantially including random). Further, the random number value is generated while controlling the appearance order before and after, that is, the appearance order in the vertical direction and the appearance order in the field (or frame) direction to be aperiodic. An example of the non-periodic change of the displacement amount will be described later. It is more preferable to change the displacement amount by changing the displacement amount setting value at the timing of the vertical synchronization signal.
[0034]
The timings of the read-side reset signal 38A and the write-side reset signal 38B are set for each line based on the input random number value and the horizontal synchronization signal timing, and are output from the random number generator 38. 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 and inputs it to the adder 31. Details of the above operation will be described later.
[0035]
Normally, error data written to the line memory 36 is generally cleared (reset) to zero outside the effective video period. On the other hand, in the present embodiment, the line memory 36 is not cleared to zero even outside the effective video period, that is, in the horizontal blanking period or the vertical blanking period. Thus, as described above, when the video signal shifts from outside the effective video period to the effective video period, the lower 4 bits obtained in the target pixel immediately before reaching the effective video period are not cleared to zero, and an error occurs. Generate data.
[0036]
The adder 31 adds the input R signal and the output of the line memory 36 and inputs the sum to the adder 32. Assuming that the input R signal is the noticed dot P ′ shown in FIG. 3A or FIG. 4A, the adder 31 is error data generated in the past for approximately one line with respect to the noticed dot P ′. The operation of adding the output of the line memory 36, that is, B ′ × 3/16 + C ′ × 5/16 + D ′ × 1/16 is performed.
[0037]
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 adds error data generated in the past of one dot to the output of the adder 31 obtained by adding error data generated in the past of approximately one line to the target dot P ′. The operation of adding 7/16 is performed. As described above, error data obtained by multiplying the peripheral dots A ′ to D ′ by the respective error diffusion coefficients is added to the target dot P ′ shown in FIG. 3A or 4A. Of the 12-bit data output from the adder 32, the lower 4 bits are input to the R error detection circuit 33R, and the above operation is repeated.
[0038]
The upper 8 bits of the 12-bit data output from the adder 32 are input to the limiter 37. The limiter 37 limits and outputs the amount of data obtained by adding error data to the target dot P ′ exceeding 8 bits (overflow).
[0039]
As described above, the error data addition process for the target dot P ′ is sequentially performed for each dot. As a result, as shown in FIG. 3A or FIG. This means that the minute data is multiplied by an error diffusion coefficient of 7/16, 3/16, 5/16, 1/16 and diffused to the peripheral dots A to D.
[0040]
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, and the B error diffusion processing is performed. The error diffusion coefficient set in the B error detection circuit 33B in the circuit 3B and the number of bits used for error diffusion are the error diffusion coefficient set in the R error detection circuit 33R and the G error detection circuit 33G and the number of bits used for error diffusion. It is different from.
[0041]
FIG. 3 shows a case where the error diffusion coefficients are made different. As shown in FIG. 3B, for the B signal, the data for the lower 4 bits in the target dot P is 9/16, 2 The error diffusion coefficients of / 16, 4/16, and 1/16 are multiplied to diffuse to the peripheral dots A to D.
[0042]
In this manner, the error diffusion processing circuits 3R, 3G, and 3B perform error diffusion on one signal or all signals in the R, G, and B signals in the target pixel that is configured by three dots of the R, G, and B signals. By varying the coefficients and performing error diffusion processing on the R, G, and B signals, 12-bit data is output as 8-bit data. Note that all of the error diffusion coefficients for the peripheral dots A to D may be made different, or only some of them may be made different. In the example of FIG. 3, the error diffusion coefficient for the peripheral dot D is 1/16, and the error diffusion coefficients for the other peripheral dots A to C are different. Note that it is better to make the error diffusion coefficient slightly different than to make it significantly different.
[0043]
As described above, even in the PDP 4 having only 8-bit display capability, it is possible to display an image that can be apparently recognized as a display image equivalent to 12 bits by using the visual integration effect. Further, a common error diffusion coefficient is not used as an error diffusion coefficient for the R, G, and B signals, and the diffusion location to pixels located at least one line behind the target pixel is at least one of the R, G, and B signals. Since each signal is changed continuously and randomly for each line, even when a fixed pattern is displayed, image quality interference such as periodic pattern noise peculiar to error diffusion represented by, for example, granularity or beat shape, etc. It is very difficult to recognize visually. Therefore, a display device with higher image quality can be provided.
[0044]
FIG. 4 shows a case where the number of bits used for error diffusion is varied. As shown in FIG. 4B, for the B signal, the lower 4th bit to the lower 2nd bit in the target dot P are shown. The three bits of data up to the above are multiplied by error diffusion coefficients of 4/8, 1/8, 2/8, and 1/8, and are diffused to the peripheral dots A to D.
[0045]
In this embodiment, error diffusion is performed using 3 bits from the lower 4th bit to the lower 2nd bit in the 12-bit B signal. However, the inverse gamma correction in the inverse gamma correction circuit 2 is applied to the B signal. At the processing stage, it is configured to output an 11-bit digital signal, that is, a 2048 gradation signal with the same inverse gamma correction characteristics as the R and G signals, and the lower 3 bits of data are multiplied by the above error diffusion coefficient. Then, it may be diffused to the peripheral dots A to D.
[0046]
In this case, if the inverse gamma correction processing of the B signal is realized by a look-up table (LUT) using a read only memory (ROM), the ROM capacity can be saved accordingly. There is an effect of becoming. Further, when the inverse gamma correction processing is 11 bits, all the processing performed by the B error diffusion processing circuit 3B is a processing circuit for 3 bits, so that circuit capacity is saved. There is also an effect that the delay of about one line in the line memory 36 can be reduced by one bit.
[0047]
In this manner, the error diffusion processing circuits 3R, 3G, and 3B perform error diffusion on one signal or all signals in the R, G, and B signals in the target pixel that is configured by three dots of the R, G, and B signals. The R, G, and B signals are subjected to error diffusion processing by changing the number of bits used for, thereby outputting 12-bit data (B signal is 11 bits) as 8-bit data. It should be noted that the number of bits used for error diffusion is better to be slightly different than to be significantly different.
[0048]
As described above, even in the PDP 4 having only 8-bit display capability, an image that can be recognized as a display image equivalent to 12 bits (B signal is equivalent to 11 bits) by using the visual integration effect. Can be displayed. The number of bits used for error diffusion for the R, G, and B signals is not common, and the diffusion location to pixels located one line or more behind the target pixel is at least one signal of the R, G, and B signals. Since it is changed continuously and randomly for each line, even when displaying a fixed pattern etc., image quality disturbance such as periodic pattern noise peculiar to error diffusion represented by, for example, granularity or beat shape is very visually It is hard to be recognized. Therefore, a display device with higher image quality can be provided.
[0049]
In this 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. However, the number of bits used for error diffusion is 3 bits or 4 bits. It is not limited to. It is preferable that not all of the lower bits of the first number of bits, which are the difference between the first number of bits and the second number of bits, be used for error diffusion, but a part thereof is used for error diffusion. As described above, the higher-order bits consecutive from the most significant bit (the lower-order fourth bit in the above example) of the lower-order bits are used.
[0050]
In this embodiment, the number of bits used for error diffusion of the R and G signals is 4 bits, and the error diffusion coefficients of the respective peripheral dots are the same. However, the error diffusion coefficients of the peripheral dots may be different.
[0051]
As an example, for the R signal, as shown in FIG. 5 (A), the error diffusion coefficients of 7/16, 3/16, 5/16, 1/16 are added to the data of the lower 4 bits in the target dot P. To the surrounding dots A to D, and for the G signal, as shown in FIG. 5B, the lower 4 bits of the data of the target dot P are 9/16, 2/16, The error diffusion coefficients of 4/16 and 1/16 are multiplied and diffused to the peripheral dots A to D. For the B signal, as shown in FIG. 4/8, 1/8, 2/8, 1/8 error diffusion for 3 bits of data from the first to the lower 2 bits (or data for the lower 3 bits if the inverse gamma correction is 11 bits) You may make it spread to surrounding dots AD by multiplying with a coefficient.
[0052]
In this manner, the error diffusion processing circuits 3R, 3G, and 3B perform error diffusion on one signal or all signals in the R, G, and B signals in the target pixel that is configured by three dots of the R, G, and B signals. By performing error diffusion processing on the R, G, and B signals by varying the coefficients, or by varying the number of bits used for error diffusion for one signal or all signals in the R, G, and B signals , 12-bit or 11-bit data is output as 8-bit data.
[0053]
Next, a description will be given of a method of changing, for each line, the diffusion location of pixels located on the line behind the pixel of interest to dots of at least one of R, G, and B signals. In the present embodiment, as a more preferred embodiment, a case where the diffusion location is made different for each of the R, G, and B signals will be described. FIG. 6 shows an example of changing the diffusion position of pixels located at the back of at least one line behind the target pixel for each R, G, B signal, and FIG. 7 exists at least one line behind the target pixel. An example of changing the diffusion location of the pixel to the dot for each line is shown.
[0054]
First, FIG. 6 will be described. The attention dots P shown in FIGS. 6A, 6B, and 6C are pixels located at the same place, and are three dots that constitute the attention pixel. Each error diffusion coefficient diffused to the dots A, B, C, and D shown in FIG. 6 is the same as each error diffusion coefficient diffused to the dots A, B, C, and D shown in FIGS. It's okay. In FIG. 6, description of the value of each error diffusion coefficient diffusing to dots A, B, C, and D is omitted.
[0055]
For the R signal of FIG. 6A, the target dot P is diffused to the right adjacent dot A, the directly lower dot B, the lower right dot C, and the lower right pixel D. For the G signal in FIG. 6B, the target dot P is diffused to the right adjacent dot A, the lower left dot B, the direct lower dot C, and the lower right dot D. With respect to the B signal in FIG. 6C, the target dot P is diffused to the right adjacent dot A, the lower left dot B, the lower left dot C, and the lower right dot D. In this way, the diffusion locations of the pixels located behind one or more lines of the pixel of interest (here, the pixels located behind one line) to the dots are made different for each of the R, G, and B signals.
[0056]
The R error diffusion processing circuit 3R, the G error diffusion processing circuit 3G, and the B error diffusion processing circuit 3B shown in FIG. 2 have the same circuit configuration, but R, G, and B signals as shown in FIG. The change of the diffusion location for each line can be easily realized, for example, by shifting the 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 of the diffusion location is realized by shifting the reading start position of the line memory 36, as shown in FIG. 6, the relative positional relationship between the dots B, C, and D (the order and the distance between the dots). Is not changed.
[0057]
The present invention is not limited to this, and the relative positional relationship between the dots B, C, and D may be shifted within the same line, or the dots B, C, and D may be positioned on different lines. Good. For example, the R signal may be diffused one line below the target dot P, the G signal may be diffused two lines below the target dot P, and the B signal may be diffused three lines below the target dot P. Further, for example, the relative positions of the dots B, C, and D with respect to the target pixel P including the dot A may be changed for each field. The start position of the write side reset signal in the line memory 36 may be shifted, or both the write side reset signal and the read side reset signal may be shifted.
[0058]
Next, FIG. 7 will be described. In FIG. 7, the first line to the fifth line... Represent the display lines of the PDP 4. It is assumed that the attention dot P is at the position shown in FIG. The target dot P is one of R, G, and B signals, and the dots B to N shown in the second and subsequent lines are signals of the same color as the target dot P.
[0059]
The error data is diffused from the attention dot P on the first line to the dot A on the right, the dot B immediately below, the dot C on the lower right, and the dot D on the lower right of the pixel. The error data is diffused to the surrounding pixels in the first line in the same manner except for the noticed dot P shown in the figure. Are diffused as D. Each error diffusion coefficient diffusing to the dots A, B, C, and D shown in FIG. 7 is the same as each error diffusion coefficient diffusing to the dots A, B, C, and D shown in FIGS. It's okay. In FIG. 7, the description of the value of the number of error diffusion coefficients each diffusing to dots A, B, C, and D is omitted.
[0060]
Next, in the second line, the dot B is the attention dot, in the third line, the dot F is the attention dot, and in the fourth line, the dot J is the attention dot. From the noticed dot B on the second line, it diffuses to the dot C on the right side, the dot E on the lower left, the dot F just below, and the dot G on the lower right. The value of the error diffusion coefficient that diffuses to the right adjacent dot C, the lower left dot E, the directly lower dot F, and the lower right dot G is the dot A, B, C, and D that diffuses from the target dot P on the first line. It is the same as each error diffusion coefficient.
[0061]
From the noticed dot F on the third line, it diffuses to the right adjacent dot G, the lower left dot H, the lower left dot I, and the lower right dot J. The value of the error diffusion coefficient that diffuses to the right adjacent dot G, the lower left dot H, the lower left dot I, and the directly lower dot J is the dot A, B, C, D that diffuses from the target dot P on the first line. It is the same as each error diffusion coefficient in. From the noticed dot J on the fourth line, it diffuses to the dot K on the right, the dot L directly below, the dot M on the lower right, and the dot N on the lower right of the pixel. The value of the error diffusion coefficient that diffuses to the right adjacent dot K, the right lower dot L, the lower right dot M, and the second lower right dot N is the dot A, B, C diffused from the target dot P of the first line. , D are the same as the respective error diffusion coefficients.
[0062]
The R error diffusion processing circuit 3R, the G error diffusion processing circuit 3G, and the B error diffusion processing circuit 3B shown in FIG. 2 have the same circuit configuration, but the diffusion locations for each line as shown in FIG. The change can be easily realized, for example, by shifting the read start position of the read side reset signal of each line memory 36 for each line. If the change of the diffusion location is realized by shifting the reading start position of the line memory 36, as shown in FIG. 7, the relative positions of the dots positioned one line behind the target dot P, B, F, J. The positional relationship (order and distance between each dot) is not changed.
[0063]
The present invention is not limited to this, and by shifting the relative positional relationship of each of the three dots positioned behind one line within the same line, or by switching the position of the rear line that diffuses for each line, 3 Two dots may be positioned on different lines. For example, the target dot P on the first line diffuses down one line, the target dot B on the second line diffuses down two lines, the target dot F on the third line diffuses down three lines, etc. Then, the diffusion distance in the line direction may be varied. Furthermore, for example, for each field or frame, the relative position with respect to the target pixel may be changed, including the dot located on the same line as the target pixel (dot A in the first line).
[0064]
The start position of the write side reset signal in the line memory 36 may be shifted, or both the write side reset signal and the read side reset signal may be shifted.
[0065]
FIG. 8 is a timing chart showing an example when the change of the diffusion location shown in FIG. 7 is performed by shifting both the write side reset signal and the read side reset signal of the line memory 36. As shown in FIGS. 8A to 8E, with reference to the position of the read-side reset of the first line, the delay amount between the read-side reset and the write-side reset (the time when the read-side reset is slightly shorter than one line) Setting is kept constant, and after the second line, both reset signal start positions are simultaneously shifted to the plus side and the minus side to change the diffusion location.
[0066]
In the example of FIG. 2, the random number generator 38 is used to change the spreading location as shown in FIG. 8, but the means for changing the spreading location is not limited to the random number generator. For example, a generation circuit to which an M series is applied may be used. The specific means for changing the diffusion location is arbitrary.
[0067]
Here, a specific example of a non-periodic error data diffusion method will be described with reference to FIG. In FIG. 9, the vertical direction indicates line numbers, and the horizontal direction indicates field (or frame) numbers. The video signal supplied to the display device of FIG. 1 can be an interlace signal or a non-interlace signal depending on the driving mode of the PDP 4. The example of FIG. 9 shows the case where the displacement amount of the pixel for diffusing the error data is set to 8 types including 3 pixels in the right direction and 4 pixels in the left direction, including 0 pixels that are not displaced as described above. Yes. In FIG. 9, the left direction is shown as + (plus) and the right direction is shown as-(minus). The example of FIG. 9 does not show the same state as FIG.
[0068]
As shown in FIG. 9, in the field (frame) 1, the displacement amount of the line 1 which is the highest line in the effective video period of the video signal is +4, the displacement amount of the next line 2 is +3, and the next line 3 The amount of displacement is -2. As described above, in this embodiment, the displacement amount of the pixel diffusing 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 for all the 480 lines. However, in order to simplify the circuit or software, the present embodiment is as follows.
[0069]
That is, eight lines 1 to 8 shown in FIG. 9 are defined as one area, and the displacement amount is selected aperiodically within the one area. In this example, the same amount of displacement is prevented from appearing within one region. Although not shown in the drawing, the same displacement amount as that of the lines 1 to 8 is set for the lines 9 to 16 as the next area. If it does in this way, it will become periodic if it sees between several area | regions, but it is aperiodic and substantially random within one area | region.
[0070]
Further, 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. . As described above, in this embodiment, the displacement amount of the pixel for diffusing the error data is sequentially changed within the displacement amount setting value for each field or frame screen. Although it is preferable to always set the amount of displacement at random in the field (frame) direction, in the present embodiment, the following is performed in order to simplify the circuit or software.
[0071]
In other words, eight fields (frames) 1 to 8 shown in FIG. 9 are defined as one time region, and the displacement amount is selected aperiodically within the one time region. The range surrounded by the thick solid line is the one hour region. In this example, the same displacement amount is prevented from appearing in the one-hour region. Although not shown in the drawing, the displacement amount is the same as that in the fields (frames) 1 to 8 in the fields (frames) 9 to 16 that are the next one-hour areas. If it does in this way, it will become periodic if it sees between several time domain, but it is aperiodic and substantially random within one time domain.
[0072]
This embodiment is also sufficiently effective in terms of preventing image quality disturbances such as vertical and oblique beat-like images and granular still images.
[0073]
【The invention's effect】
As described above in detail, according to the error diffusion processing method of the display device of the present invention, it appears when error diffusion processing is performed on an image having a large area of a low gradation portion in a very dark portion. It is possible to extremely effectively reduce image quality interference such as periodic pattern noise. Also, even if the brightness of the panel increases and the brightness step difference in the low gradation part increases, the light emission probability (number of times of light emission) of each dot by a certain area is further averaged, so that there are many areas near the low gradation Even if appears, the feeling of noise caused by error diffusion is not felt, and the deterioration of image quality due to the increase in the brightness of the panel can be suppressed as much as possible.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a display device using an error diffusion processing method of the present invention.
2 is a block diagram showing a specific configuration example of an error diffusion processing circuit 3 in FIG. 1. FIG.
FIG. 3 is a diagram for explaining a preferred example of an error diffusion processing method of the present invention.
FIG. 4 is a diagram for explaining a preferred example of an error diffusion processing method of the present invention.
FIG. 5 is a diagram for explaining a preferred example of an error diffusion processing method of the present invention.
FIG. 6 is a diagram for explaining a preferred example of the error diffusion processing method of the present invention.
FIG. 7 is a diagram for explaining an error diffusion processing method of the present invention.
FIG. 8 is a diagram for explaining an error diffusion processing method of the present invention.
FIG. 9 is a diagram for explaining an error diffusion processing method of the present invention.
FIG. 10 is a diagram showing a conventional example.
[Explanation of symbols]
1 Video signal processing circuit
2 Inverse gamma correction circuit
3 Error diffusion processing circuit
4 PDP

Claims (4)

When reducing the video signal having the first number of bits to the second number of bits that is smaller than the first number of bits, each pixel of interest formed of a plurality of dots forming color components The pixel of interest is located in error data obtained by multiplying at least a part of lower bits of the first bit number, which is the difference between the first bit number and the second bit number, by a predetermined error diffusion coefficient. In an error diffusion processing method of a display device that diffuses to a plurality of peripheral pixels including a plurality of pixels located in a line behind the line,
When at least a part of a plurality of lines within the effective video period of the video signal is defined as one area, the position in the line direction of the target dot that is the color component in the target pixel is set as a reference position within the one area, and the error The diffusion positions of a plurality of dots located in the rear line for diffusing data are displaced aperiodically for each line within the range of the number of dots set in the horizontal direction from the reference position , and adjacent 2 The error data diffusion position from the same reference position in the line direction in two lines is not the same,
When the one area over a plurality of screens that are a plurality of fields or a plurality of frames is defined as a one-hour area, a plurality of lines positioned in the rear line that diffuses the error data in each line in the one-hour area. The dot diffusion position is displaced aperiodically for each screen within a predetermined number of dots in the left-right direction from the reference position , and the same reference position in the line direction on the same line of two adjacent screens An error diffusion processing method for a display device, characterized in that the diffusion positions of the error data from the same are not the same.   When shifting from outside the effective video period of the video signal to the effective video period, the lower-order bits of the first number of bits obtained at the pixel of interest immediately before reaching the effective video period are not cleared to zero, and the error 2. The error diffusion processing method for a display device according to claim 1, wherein data is generated.   The color component is an R, G, B signal, and an error diffusion coefficient for at least one of the R, G, B signals in the target pixel is made different from an error diffusion coefficient for other signals. An error diffusion processing method for a display device according to claim 1 or 2.   The color components are R, G, and B signals, and the number of bits used for error diffusion for at least one of the R, G, and B signals in the pixel of interest is the number of bits used for error diffusion for other signals. 3. The error diffusion processing method for a display device according to claim 1, wherein the error diffusion processing method is different.

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