JPH09179523A - Error diffusion processor for display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display a smooth and continuous pseudo halftone image when gradation adaptive type error diffusion processing is performed by a PDP(plasma display device) of the gradation number out of a 2 factorial display. SOLUTION: A light emission luminous characteristic obtained at intervals of a fixed period for performing gradation adaptive type error diffusion processing by an error diffusion circuit 20, a data conversion circuit 14 and a light emission luminous characteristic acquisition circuit 18a is made the level answering to the light emission luminous characteristic P prescribed so that a light emission luminous level increases stepwise at the ratio of 1:1 from a level 0 to the level Dk answering to k (e.g. 12). Moreover, a correction luminance line Q used together with the light emission luminous characteristic by the light emission luminous characteristic acquisition circuit 18a in the error diffusion circuit 20 is set so as to interest with respective stages of the light emission luminance lever of the light emission luminous characteristic P. Thus, the smooth and continuous gradation is formed by gradation adaptive type error diffusion. An upper saturation part is corrected by a gammer correction circuit 24.

Description

Detailed Description of the Invention

[0001]

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

[0002]

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

[0003] PDPs are AC type and D type having different basic characteristics.
It is divided into two types of C type. In the AC type PDP, sufficient characteristics have been obtained with respect to luminance and life, but as for gradation display, only a maximum of 64 gradation display has been reported at the prototype level, but the address / display separation type driving method (ADS) A method of 256 gradations in the future by the subfield method has been proposed.

In the ADS subfield method, for example, in the case of 8 bits and 256 gradations, one frame has a relative luminance ratio of 1, 2, 4, 8, 16, 32, 64, 128.
, And 256 gradations are displayed by the combination of the luminances of the 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 above-described AC driving method, as the number of gradations increases, the number of bits in an address period as a preparation period for lighting and emitting light in the panel within one frame period increases. The period becomes relatively short, and the maximum luminance decreases. In this way, since the brightness gradation emitted from the panel surface is determined by the number of bits of the signal to be handled, if the number of bits of the signal to be handled is increased, the image quality is improved, but the light emission luminance is reduced, and conversely If the number of bits is reduced, the light emission luminance is increased, but gradation display is reduced and the image quality is deteriorated.

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

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

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

[0009]

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

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

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

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

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

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

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

[0016]

According to a first aspect of the present invention, an m (≤n-1) -bit diffused output signal is obtained from an n-bit input video signal by performing error diffusion processing using light emission luminance characteristics. An error diffusion circuit and an m-bit diffusion output signal obtained by this error diffusion circuit are time-divided into a plurality of subfields in one frame, and the number of display gradations k (<2 to the m-th power)
The data conversion circuit that converts into a drive signal for displaying a halftone image on the display panel and the emission brightness of the display panel that corresponds to the preset emission brightness characteristics based on the drive signal obtained by this data conversion circuit It comprises a light emission luminance characteristic acquisition circuit for obtaining the characteristic at regular intervals and a memory storing a preset correction luminance line, and the set light emission luminance characteristic changes from level 0 of the drive signal to the number of display gradations k. Up to the corresponding level Dk, the emission brightness level is increased stepwise at a ratio of 1: 1, and the emission brightness level is set to repeat the maximum brightness level for a drive signal exceeding the level Dk, and set in the memory. The stored correction luminance line is set so as to intersect with the level of each step of the set emission luminance level of the emission luminance characteristic that has been set stepwise, and the error diffusion circuit is set to the luminance characteristic acquisition circuit. And performing error diffusion processing by using the corrected luminance line, which is set and stored in the light emission luminance characteristics and the memory obtained.

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

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

According to a third aspect of the present invention, in the first or second aspect of the present invention, in order to obtain the linearity of the upper saturation part, the setting among the emission luminance characteristics obtained by the emission luminance characteristic acquisition circuit is set. A gamma correction circuit that corrects the linearity between the drive signal and the light emission brightness level for the light emission brightness characteristic corresponding to the light emission brightness characteristic between the drive signal and the light emission brightness level exceeding the level Dk of the generated light emission brightness characteristic is provided. It will be.

[0020]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0035]

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

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

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

[Brief description of the drawings]

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

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

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

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

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

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

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

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

[Explanation of symbols]

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Onodera 1116 Suenaga, Takatsu-ku, Kawasaki-shi, Kanagawa Within Fujitsu General Co., Ltd.

Claims (3)

[Claims] 1. An error diffusion process using light emission luminance characteristics is performed to convert m (≦ n−) from an n-bit input video signal.
1) An error diffusion circuit for obtaining a bit diffusion output signal and an m-bit diffusion output signal obtained by the error diffusion circuit
A data conversion circuit that time-divides a frame into a plurality of subfields and converts into a drive signal for displaying a halftone image on a display panel with a display gradation number k (<2 to the m-th power), and this data conversion circuit A light emission luminance characteristic acquisition circuit for obtaining the light emission luminance characteristic of the display panel corresponding to a preset light emission luminance characteristic at regular intervals based on the obtained drive signal, and a memory storing a preset corrected luminance line. Equipped with,
With respect to the set emission luminance characteristic, the emission luminance level gradually increases from the level 0 of the drive signal to the level Dk corresponding to the number of display gradations k at a ratio of 1: 1, and the drive signal exceeds the level Dk. The emission luminance level is set so as to repeat the maximum luminance level, and the correction luminance line set and stored in the memory has a stepwise increase in the emission luminance level of the set emission luminance characteristic. The error diffusion circuit is set to intersect with the level, and the error diffusion circuit performs an error diffusion process using the emission luminance characteristic obtained by the luminance characteristic acquisition circuit and the corrected luminance line set and stored in the memory. Error diffusion processing device for display device. 2. A data conversion circuit time-divisionally divides an m-bit diffused output signal obtained by an error diffusion circuit into a plurality of subfields including at least two subfields having equal weighting, and a display gradation is displayed. The error diffusion processing device for a display device according to claim 1, wherein the error diffusion processing device is converted into a signal for displaying a halftone image on the display device of several k (<2 m-th power). 3. A light emission luminance characteristic corresponding to a light emission luminance characteristic between a drive signal and a light emission luminance level exceeding a set light emission luminance characteristic level Dk among the light emission luminance characteristics obtained by a light emission luminance characteristic acquisition circuit. 3. The error diffusion processing device for a display device according to claim 1, further comprising a gamma correction circuit that corrects the linearity between the drive signal and the emission luminance level.