JP3334401B2 - Error diffusion processing device for display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an error diffusion processing device for a display device which performs pseudo halftone display by error diffusion.

[0002]

2. Description of the Related Art Recently, as a thin and lightweight display device, P
DP (plasma display panel) has attracted attention. The driving method of this PDP is completely different from the conventional CRT driving method, and is a direct driving method using digitized video input signals. Therefore, the luminance gradation emitted from the panel surface is determined by the number of bits of the signal to be handled. PDP is Ru divided into AC type and a DC type 2 system having different basic properties.

[0003] In the AC type PDP, sufficient characteristics have been obtained with respect to luminance and lifetime. However, as for gradation display, only a maximum of 64 gradation display has been reported at the prototype level, but the address / display separation type has been reported. A method of 256 gradations in the future by a driving method (ADS subfield method) has been proposed.

One frame has a relative luminance ratio of 1, 2,
It is composed of eight subfields of 4, 8, 16, 32, 64 and 128, and displays 256 gradations by combining the luminance of eight screens. Each subfield is composed of an address period in which data for one refreshed screen is written and a sustain period for determining a luminance level of the subfield. In the address period, first, wall charges are initially formed on each pixel at the same time for the entire screen, and then a sustain pulse is applied to the entire screen to perform display. The brightness of the subfield is proportional to the number of sustain pulses and is set to a predetermined brightness. In this way, 256 gradation display is realized.

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

The error diffusion process for minimizing the shading error between the input signal and the emission luminance while reducing the number of bits of the output drive signal from the number of bits of the input signal is a process for expressing a pseudo halftone. , Which is used when expressing gradation with a small number of gradations. In a conventional general error diffusion circuit, a video signal of an original pixel Ai, j of p (for example, 8) bits is input from a video signal input terminal to the error diffusion circuit, and the number of bits is further reduced to q ( For example, 4) light is emitted from the PDP by performing processing for reducing the number of bits.

A light emission luminance characteristic calculation unit such as a ROM measures and stores the light emission luminance characteristic of the PDP from representative input data (solid line) as close as possible to y = x (dotted line) shown in FIG. Keep it. This light emission luminance characteristic is sent to an error amount calculation unit to calculate an error, which is added to an input video signal by a processing circuit unit and diffused to perform pseudo halftone display.

As a result, although the light emission luminance level is instantaneously like a stair-like solid line, it is actually recognized in an averaged state, and becomes a corrected luminance line similar to the dotted line y = x. .

However, the light emission luminance characteristics of a display device such as a PDP vary depending on data to be displayed, and there are cases where the light emission luminance characteristics deviate greatly from y = x (dotted line) as shown by a solid line in FIG. . In such a case, according to the method of adjusting to the typical emission luminance characteristics as shown in FIG. 6, data other than when the representative characteristics are obtained cannot be adapted to the gradation characteristics. There has been a problem that a pseudo contour due to gradation non-adaptation appears.

Therefore, the applicant of the present invention has proposed a ROM
Instead of the light emission luminance characteristic given from the above, the light emission luminance characteristic for each of one or more frames is calculated based on the luminance deviation characteristic obtained from the load factor of input data of a display device such as a PDP, and is calculated for one or more frames. We proposed a device that updates the light emission luminance characteristics every time and performs error diffusion to prevent the appearance of false contours.

To explain this with reference to FIG. 7, a reproduced output signal is obtained by adding a reproduction error generated in the past from an original pixel by an error diffusion circuit 11 to a quantized input original pixel video signal to obtain a pseudo halftone. In the display device, a light emission luminance characteristic acquisition circuit 20 is coupled to the error diffusion circuit 11, and the light emission luminance characteristic acquisition circuit 20 converts M bits of video data by M counters corresponding to each bit. A display number counter 21 for counting the number of display of each bit in one or a plurality of frames;
A display area ratio calculation unit 22 that calculates the display area ratio (Sk) by dividing the number of display dots counted by the above by the total number of dots.
A light emission luminance deviation characteristic measuring unit 23, which comprises a ROM, and obtains a luminance deviation characteristic of each bit; a luminance deviation amount calculating unit 24, which obtains a luminance deviation amount of each level based on data of the light emission luminance deviation characteristic measuring unit 23; Is an error diffusion processing device for a display device.

The operation of the above configuration will be described. The error diffusion circuit 11 performs an error diffusion process by the error amount calculation unit 12 and the processing circuit unit 13 based on the given light emission luminance characteristics, and performs pseudo halftone display. When data is transmitted from the error diffusion circuit 11 to the light emission luminance characteristic acquisition circuit 20, the display number counter 21 converts the M-bit video data into one or a plurality of frames of each bit by M counters corresponding to each bit. The number of display dots in the sub-field K, that is, the number of displayed dots, is counted. The display area ratio calculation unit 22 calculates the display area ratio (Sk) by dividing the “number of display dots of the subfield K” counted by the display number counter 21 by the “total number of dots”.
Then, the luminance deviation characteristic of each bit is obtained by the light emission luminance deviation characteristic measuring section 23, and the luminance deviation amount of each level is obtained by the luminance deviation amount calculating section 24 via the maximum luminance calculating section 25 as necessary.

When this is expressed by an equation, the light emission luminance level Yn of an arbitrary input level n is determined by taking into account the luminance deviation depending on the display area ratio (Sk) of each subframe. Is performed by the light emission luminance characteristic acquisition circuit 20. Here, the luminance deviation characteristic (δ) obtained from the display area ratio (Sk) and the load ratio of the input data is generally a characteristic line as shown in FIG. 3, and the function for obtaining this δ is a light emission luminance deviation characteristic. It is stored in the measuring unit 23.

The calculation of the luminance deviation amount of each level is as follows. This is transmitted to the error diffusion circuit 11 after updating the gradation characteristic for every one or a plurality of frames. Error diffusion circuit 11
Then, based on the light emission luminance characteristics, error diffusion processing is performed and output to a PDP. With such a configuration, when the light emission luminance characteristic is changed by data to be displayed as shown by a solid line, a dotted line, and a chain line in FIG. 5, the gradation characteristic is updated accordingly. Then, since the luminance is not adjusted to a typical light emission luminance characteristic as in the related art, it is possible to sufficiently adapt to the gradation characteristic even for data that changes every moment.

[0015]

However, since the gradation characteristic is updated every one or a plurality of frames as described above, the gradation linearity is improved, but the diffusion noise particularly in a low-level image is visually recognized. There was a problem of being noticeable. That is,
At a low level, the whole image is dark and close to a black level, so that there is a problem that even if the diffusion pattern is a slight white spot, it is visually conspicuous.

According to the present invention, the light emission luminance characteristic for each frame or a plurality of frames is calculated based on the luminance deviation characteristic obtained from the load factor of the input data of the display device, and is updated to perform error diffusion, thereby performing pseudo contour. It is an object of the present invention to obtain a device which prevents the appearance of the noise, especially in which the diffusion noise at low levels is inconspicuous.

[0017]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and an error diffusion circuit 11 generates a quantized input original pixel video signal in the past from the original pixel. In a device for adding a reproduction error to obtain a diffused output signal and perform pseudo halftone display, a light emission luminance characteristic acquisition circuit 20 is coupled to the error diffusion circuit 11, and this light emission luminance characteristic acquisition circuit 20 Display data counter 21 that counts the number of displays in one or a plurality of frames of each bit by using M counters corresponding to each bit of the video data of A display area ratio calculation unit 22 for calculating a display area ratio (Sk) by dividing by a number;
A light emission luminance deviation characteristic measuring section 23 for obtaining a luminance deviation characteristic of each bit; a luminance deviation amount calculating section 24 for calculating and outputting a luminance deviation amount based on data of the light emission luminance deviation characteristic measuring section 23; An error diffusion processing device for a display device, comprising: an adding unit 28 for adding a constant value to the luminance deviation amount obtained by the amount calculating unit 24 to obtain a light emission luminance level larger than the actual value.

[0018]

In the error diffusion circuit 11, the luminance deviation amount of a level other than the low level, which is constantly updated by the luminance deviation amount calculating unit 24, and the fixed luminance deviation amount set in advance by the fixed constant generation unit 27, And performs error diffusion processing based on the light emission luminance characteristics of the above, and outputs the result to the PDP. For this reason, even if the light emission luminance characteristic changes according to the data to be displayed, the light emission luminance characteristic is not adjusted to the representative light emission luminance characteristic, so that it can sufficiently adapt to the gradation characteristic even for data that changes every moment.
At this time, since the light emission luminance level is set to be higher than the actual light emission level in the adding unit 28, the generation of noise at a low level is reduced.

[0019]

An embodiment of the present invention will be described below with reference to FIG. PD driven by the address / display separated driving method (ADS subfield method) as a display device
The case where P is used will be described as an example. The number N of display gradations that can be achieved by the ADS subfield method is the number of subfields M
Determined by That is, N = 2 to the power of M.

An ideal light emission luminance level Yn of an arbitrary input level n is obtained by binary-converting n, It is expressed as Actually, since there is a luminance deviation depending on the display area ratio (Sk) for each subframe, It is expressed as Here, δ: luminance deviation characteristic obtained from the load factor of input data It is.

In FIG. 1, the error diffusion processing device comprises an error diffusion circuit 11 and a light emission luminance characteristic acquisition circuit 20. As described with reference to FIG. 7, the error diffusion circuit 11 performs an error diffusion process by the error amount calculation unit 12 and the processing circuit unit 13 based on the given light emission luminance characteristics, The display is performed.

The light emission luminance characteristic acquisition circuit 20 comprises a display number counter 21, a display area ratio calculation unit 22, a light emission luminance deviation characteristic measurement unit 23, and a luminance deviation amount calculation unit 24.
The present invention is for obtaining emission luminance characteristics for each one or a plurality of frames from video data driven by DP, and transmitting the obtained emission luminance characteristics to the error diffusion circuit 11 during a vertical synchronization period of an image. Then, the luminance deviation amount calculation unit 2
An addition unit 28 is interposed between the error amount calculating unit 12 and the error amount calculating unit 12. By adding a constant value by the adding unit 28, the light emission luminance level of the luminance deviation amount calculating unit 24 is uniformly increased. To make it a bit darker and reduce noise, especially at low levels.

More specifically, the display number counter 21
It is composed of M counters, and counts the number of display of each bit in one or a plurality of frames by a counter corresponding to each bit of M-bit video data. The display area ratio calculation unit 22 calculates the display area ratio (Sk) by dividing the “number of display dots of the subfield K” counted by the display number counter 21 by the “total number of dots”. . The emission luminance deviation characteristic measuring unit 23 includes:
It is made up of an LUT (Look Up Table) such as a ROM, and determines the luminance deviation characteristics of each bit. The luminance deviation amount calculating section 24 calculates the luminance deviation amount of each level, and updates the gradation characteristics of data other than low-level data for every one or a plurality of frames. The adder 2
8 is a high-level line 30 of the luminance deviation calculating section 24.
To the output of the low level line 31, a constant value (for example, 1) input to the input terminal 29 is uniformly added. The high-level line 30 is directly connected to the error amount calculation unit 1 as indicated by a dotted line.
2 and a constant value (for example, 1) input to the input terminal 29 by the adding unit 28 may be added only to the low-level line 31.

The operation of the above configuration will be described.
The display number counter 21 is a M-number of counters corresponding to each bit of M-bit video data.
The number of displayed dots "is counted. Display area ratio calculation unit 2
2 calculates the display area ratio (Sk) by dividing the "number of display dots of the subfield K" counted by the display number counter 21 by the "number of total dots". Then, the luminance deviation characteristic of each bit is obtained by the light emission luminance deviation characteristic measuring section 23, and the luminance deviation amount of each level is obtained by the luminance deviation amount calculating section 24 based on the luminance deviation characteristic.

When this is expressed by an equation, the light emission luminance level Yn of an arbitrary input level n is determined by taking into account the luminance deviation depending on the display area ratio (Sk) of each subframe. Is performed by the light emission luminance characteristic acquisition circuit 20. Here, the luminance deviation characteristic (δ) obtained from the display area ratio (Sk) and the load ratio of the input data is generally a characteristic line as shown in FIG. 3, and the function for obtaining this δ is a light emission luminance deviation characteristic. It is stored in the measuring unit 23.

The calculation of the luminance deviation amount of each level is as follows. This is updated every one or a plurality of frames, and a constant value is added by the adder 28 and transmitted to the error diffusion circuit 11. The error of the error diffusion is represented by the following equation: error = input level−light emission luminance. When the addition unit 28 uniformly adds a constant value to the calculated light emission luminance from the high level line 30 to the low level line 31, As shown by the dotted line 2, the emission luminance is increased as a whole, and the error is reduced accordingly, so that the number of lighting dots is reduced. In this case, even if the addition value from the low level to the high level is a constant value, the addition ratio at the low level is large, so that the noise reduction effect is greater at the low level than at the high level. This means that substantially the same noise reduction effect can be obtained even when a fixed value is applied only to the low level line 31. In this way, by calculating the light emission luminance higher, reducing the error and reducing the number of lighting dots, the image after error diffusion becomes slightly darker, and the effect of reducing the diffusion noise in the low-level image portion can be obtained. , It will be a natural image. The error diffusion circuit 11 performs error diffusion processing based on the luminance deviation amount obtained by adding a constant value to the data updated by the luminance deviation amount calculation unit 24 and outputs the data to the PDP. With such a configuration, even if the light emission luminance characteristic changes according to the data to be displayed, the light emission luminance characteristic does not match the representative light emission luminance characteristic. It can adapt to the characteristics and prevent the generation of noise at low levels.

As another embodiment of the present invention, as shown by a dashed line in FIG. 1, a maximum luminance calculating section 25 is inserted between the emission luminance deviation characteristic measuring section 23 and the luminance deviation amount calculating section 24. Therefore, the operation up to the emission luminance deviation characteristic measuring unit 23, that is, the display number counter 21 converts the M-bit video data into M counters corresponding to the respective bits by using the display number of each bit in one or a plurality of frames. A certain “number of display dots of the subfield K” is counted. The display area ratio calculation unit 22 calculates the display area ratio (Sk) by dividing the “number of display dots of the subfield K” counted by the display number counter 21 by the “total number of dots”. Then, the luminance deviation characteristic of each bit is obtained by the light emission luminance deviation characteristic measuring unit 23. Up to this point, it is the same as in the above embodiment.

By inserting the maximum luminance calculating section 25, the luminance at the maximum input level is calculated. That is, in the case of the emission luminance characteristics as shown by the dotted line in FIG.
The maximum luminance calculation unit 25 Is calculated. Therefore, when the luminance at the maximum input level deviates from the y = x line, y = ax, the overall input level is corrected so as to approach the y = x line.
As a result, the characteristics of the dotted line in FIG. 4 are converted into the characteristics of the solid line.

Based on this data, the luminance deviation amount calculation unit 2
In 4, the luminance deviation amount of each level is calculated by the following equation. The luminance deviation amount is calculated by the luminance deviation calculating section 24 and is updated every one or a plurality of frames, and is added to a constant value by the adding section 28 and transmitted to the error diffusion circuit 11. In the error diffusion circuit 11,
Based on the luminance deviation obtained by adding a constant value to the data updated every moment by the luminance deviation calculating section 24, error diffusion processing is performed and output to the PDP. With such a configuration, even if the light emission luminance characteristic changes according to the data to be displayed, the light emission luminance characteristic does not match the representative light emission luminance characteristic. It can adapt to the characteristics and prevent the generation of noise at low levels.

[0030]

(1) According to the present invention, the light emission luminance characteristic for each one or a plurality of frames is calculated based on the luminance deviation characteristic obtained from the load factor of the input data, and the light emission luminance for each one or a plurality of frames is calculated. Since the error is diffused by updating the characteristics, appearance of a pseudo contour can be prevented. The emission luminance was calculated actually from the enhanced simultaneously lit dot and reduce the error
By reducing the bets, image after error diffusion darkened, especially the effect of reducing the diffusion noise in the low-level image portion is obtained, and natural images.

(2) When the luminance at the maximum input level deviates from the line of y = x, a maximum luminance calculation unit 25 for correcting the maximum input level as a whole so as to approach the line of y = x is provided. Therefore, error diffusion is performed more accurately, and appearance of a false contour can be prevented.

[0032]

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an error diffusion processing device of a display device according to the present invention.

FIG. 2 is a characteristic diagram showing an example of light emission luminance characteristics in the case of the device of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a light emission luminance deviation and a display area ratio.

FIG. 4 is a characteristic diagram illustrating an example of light emission luminance characteristics.

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

FIG. 6 is a characteristic diagram showing a typical example of light emission luminance characteristics.

FIG. 7 is a block diagram showing an error diffusion processing device of a display device previously proposed by the present applicant.

[Explanation of symbols]

10 video signal input terminal, 11 error diffusion circuit, 12
Error amount calculation unit, 13 processing circuit unit, 14 light emission luminance characteristic calculation unit, 20 light emission luminance characteristic acquisition circuit, 21 display number counter, 22 display area ratio calculation unit, 23 light emission luminance deviation characteristic measurement unit, .., 24... Luminance deviation calculating section, 25... Maximum luminance calculating section, 26... Low-level output terminal, 27. ... Low level output line.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hayato Denda 1116, Suenaga, Takatsu-ku, Kawasaki, Kanagawa Prefecture Inside Fujitsu General Limited (72) Inventor Seiji Matsunaga 1116, Suenaga, Takatsu-ku, Kawasaki City, Kanagawa Fujitsu General Limited Examiner Mikio Suzuno (56) References JP-A-8-179938 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G09G 3/28 G09G 3/20 G09G 3/36

Claims (4)

(57) [Claims] An apparatus for performing pseudo halftone display by adding a reproduction error generated in the past from an original pixel by an error diffusion circuit to a quantized input original pixel video signal to obtain a diffused output signal. A light emission luminance characteristic acquisition circuit 20 is coupled to the error diffusion circuit 11, and the light emission luminance characteristic acquisition circuit 20 converts M bits of video data into one or more of each bit by M counters corresponding to each bit. Display number counter 21 for counting the number of displays in a frame
And the display area ratio (Sk) is calculated by dividing the number of display dots counted by the display number counter 21 by the total number of dots.
And a light emission luminance deviation characteristic measuring unit 2 comprising a ROM and calculating a luminance deviation characteristic of each bit.
3 and a luminance deviation calculating section 24 for calculating and outputting a luminance deviation based on the data of the emission luminance deviation characteristic measuring section 23.
And an adder (28) for adding a fixed value to the luminance deviation calculated by the luminance deviation calculator (24) to obtain a light emission luminance level larger than the actual level. 2. An apparatus for performing pseudo halftone display by adding a reproduction error generated in the past from an original pixel by an error diffusion circuit 11 to a quantized input original pixel video signal to obtain a diffusion output signal. A light emission luminance characteristic acquisition circuit 20 is coupled to the error diffusion circuit 11, and the light emission luminance characteristic acquisition circuit 20 converts M bits of video data into one or more of each bit by M counters corresponding to each bit. Display number counter 21 for counting the number of displays in a frame
And the display area ratio (Sk) is calculated by dividing the number of display dots counted by the display number counter 21 by the total number of dots.
And a light emission luminance deviation characteristic measuring unit 2 comprising a ROM and calculating a luminance deviation characteristic of each bit.
3, a maximum brightness calculator 25 for calculating the brightness at the time of the maximum input level, and a brightness deviation calculator 24 for calculating and outputting a brightness deviation based on the data of the maximum brightness calculator 25.
And an adder (28) for adding a fixed value to the luminance deviation calculated by the luminance deviation calculator (24) to obtain a light emission luminance level larger than the actual level. 3. The error diffusion processing device for a display device according to claim 1, wherein the adding section adds a constant value to all display levels. 4. The error diffusion processing device for a display device according to claim 1 , wherein the adding unit adds a constant value only to a low display level.