JPH10301533A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the loss of gradation information due to an inverse gamma correction and also to reduce pseudo contours in a moving picture by increasing displayable number of gradations and converting digital data into those having an increased number of gradations at the time of applying the inverse gamma correction conversion to the data. SOLUTION: The video signal inputted from an input terminal 1 is converted into 8-bit digital data at an A/D converting part 3 and the data are subjected to a code conversion to become 9-bit digital data at a code converting part 4. The code converting part 4 codes the data by expressing the converted result of having gradations larger than the gradations of the data outputted from the A/D converting part 3 while performing the inverse gamma correction. As a result, the loss of gradation information in low luminance areas due to the inverse gamma correction is made small. Moreover, pseudo contours of the moving picture in a halftone are reduced by coding the data so that an added subfield surely emits light in the intermediate part between the gradations.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display apparatus for displaying a halftone by dividing a video signal of one field into subfields, such as a plasma display panel (PDP).

[0002]

2. Description of the Related Art In a display device such as a plasma display device in which a display output shows a non-linear characteristic, particularly a saturation characteristic with respect to the magnitude of an input voltage, a normal amplitude-modulated video signal can be correctly obtained as it is. Cannot display halftone. Therefore, the time of one field is divided into a plurality of subfields, and the relative ratio of the time displayed for each subfield is 1: 2: 4: 8:.
The halftone display is realized by changing each power of 2 and displaying or not displaying each subfield for each pixel.

In the following, a case of a display device using a self-luminous device will be described as an example. However, the device is not limited to a device that emits light by itself. Even when a device that switches between display and non-display by changing the rate or the like for each pixel is used, the halftone can be displayed by combining display and non-display of each subfield in exactly the same manner.

FIG. 6 is a diagram showing an example of a light emission sequence for explaining a conventional display device. In the figure, SF8 to SF1 indicate subfields, and in the example of the figure, one field is divided into eight subfields. Each subfield is divided into an address period and a sustain discharge period, and light emission is actually performed in the sustain discharge period. The relative ratio of the sustain discharge period in each subfield is SF8, SF7, SF6, SF5, SF4, 1SF.
3, SF2, SF1: 128: 64: 32: 26:
8: 4: 2: 1. By combining the light emission and non-light emission of these subfields, a halftone of 256 gradations can be displayed.

For example, when displaying a gray scale of 127, SF7, SF6, SF5, SF4, SF3, SF
2, SF1 emits light, and SF8 does not emit light. Since the human eye has an integration effect in the time direction, it does not respond to the blinking of light emission within the period of one field, and SF7, SF6, S
F5, SF4, SF3, SF2 and SF1 are integrated and 1
It is perceived that a gradation of 27 is displayed.

Generally, when a video signal is subjected to digital signal processing, it is quantized to 6 to 10 bits or more according to the purpose. Here, the case of quantizing to 8 bits will be described. Even if the number of quantization bits is changed, only the number of subfield divisions is changed, and there is no difference in basic operation.

When a video signal is displayed on this display device, the video signal is first converted into an 8-bit digital signal, the most significant bit (bit 8) is set to SF8, and the lower bit (bit 7) is set to SF7. Similarly, bit 6, bit 5, bit 4, bit 3, bit 2, and bit 1 are similarly assigned to SF6, SF5, SF4, SF3, S
Assign to F2 and SF1.

FIG. 7 is a block diagram of a drive circuit of a conventional display device. In the figure, reference numeral 1 denotes an input terminal for inputting a video signal, 2 denotes an input terminal for inputting a synchronizing signal, and 3 denotes an input terminal for input. A / D converter for converting the video signal into digital data, 9 is an inverse gamma converter for converting the data output from the A / D converter 3 into data after inverse gamma correction, and 5 is an inverse gamma converter 9. A frame memory unit for storing two frames of output data, a driving unit 6 for driving the display unit 7 by an output signal of the frame memory unit 5 and a control unit 8 described later, and a driving unit 7 for driving the output signal of the driving unit 6 A display unit 8 such as a PDP is a control unit that controls the A / D conversion unit 3, the inverse gamma conversion unit 9, the frame memory unit 5, and the drive unit 6 based on the synchronization signal input to the input terminal 2.

Next, the operation will be described. The control unit 8
An A / D conversion unit 3, an inverse gamma conversion unit 9, a frame memory unit 5, and a driving unit 6 are output from the synchronization signal input to the input terminal 2.
Output a predetermined control signal. The video signal input from the input terminal 1 is converted by the A / D converter 3 into 8-bit digital data.

The digital data converted by the A / D converter 3 is input to an inverse gamma converter 9. The inverse gamma converter 9 outputs output data corresponding to the input according to the conversion tables shown in Tables 1 and 2.

[0011]

[Table 1]

[0012]

[Table 2]

The relationship between input data and output data is as follows:
When the video signal input from the input terminal 1 has been subjected to gamma correction in accordance with the display characteristics of the cathode ray tube, it works as an inverse correction to the gamma correction. That is, the conversion tables (Table 1 and Table 2) are determined so that a correct halftone display is possible when the apparent luminance of the display unit 8 is changed in proportion to the output of the inverse gamma conversion unit 9. .

The data output from the data converter 4 is
The control unit 8 stores two frames at a predetermined position in the frame memory unit 5. The frame memory unit 5 has a two-frame memory, and the input digital data is alternately written to the first-frame memory and the second-frame memory for each frame.

The data stored in the frame memory unit 5 is read out from the frame memory unit 5 by the control unit 8 during the address period of SF8 shown in FIG. In this case, the data is read out of the two frame memories of the frame memory unit 5 from which data has not been written. The read data is output to the display unit 7 through the drive unit 6. After all the data of the bit 8 for all the pixels of one frame are written in the display unit 7, the display unit 7 emits light only by the predetermined pixel corresponding to the bit 8 during the sustain discharge period of SF8 by the driving unit 6. .

In the next address period of SF7, bit 7
Is read from the frame memory unit 5 and written into the display unit 7 through the drive unit 6. The display unit 7 is SF7
During the sustain discharge period, light emission is performed in the same manner as in SF8.
Here, since the ratio between the sustain discharge period of SF8 and the sustain discharge period of SF7 is 128: 64, the light emission time is half that of SF8.

Hereinafter, similarly, SF6, SF5, SF4, S
In the order of F3, SF2 and SF1, bit 6, bit 5, bit 4, bit 3, bit 2, and bit 1 corresponding to each subfield are read from the frame memory unit 5 in each address period, and The light is output to the display unit 7 through the LED 6 and emits light in accordance with the data output during each sustain discharge period. As described above, the input terminal 2
Can be displayed in halftone on the display unit 7.

In the display device configured as described above, since the inverse gamma correction is performed as shown in Tables 1 and 2, for example, when the decimal notation of the data before conversion is 20 or less, the data after conversion is The values are all 0, and the difference in gradation corresponding to the original video signal is lost. As described above, in the low luminance area, the loss of the gradation information occurs.

Further, in the display device configured to perform the halftone display configured as described above, an image that changes smoothly in the horizontal direction may move when moving on the screen in the horizontal direction or when the image is stationary. A band on the vertical stripe that was not visible (hereinafter, referred to as “false contour”) is perceived. This phenomenon is illustrated in FIG.
This will be described with reference to FIG.

FIG. 8 is a diagram showing a state of carry of an image of a conventional display device, and an image in which a carry to the most significant bit is generated in an image which smoothly changes in six horizontal pixels of interest in the horizontal direction. That is, the gradation is from 127 to 1
The image changing to 28 is shown. FIG. 9 is an explanatory diagram for explaining the phenomenon of the false contour of the conventional display device, and shows a state where the display device is moving rightward at a speed of one pixel per field. That is, FIG. 8 shows the first field of FIG. In the part of the gradation 127, the subfields SF7, SF6, SF5, SF4, SF
3, SF2, and SF1 emit light.
Only 8 emits light. When attention is paid to one pixel near the center in FIG.
7 to cause a borrow from SF8 to the lower subfield.

When a human looks at an image displayed with such a light emission pattern, his or her line of sight moves on a dashed line generally indicated by A to D. The key 127 is perceived as a gray scale 128 on the retina corresponding to a portion between the broken lines C and D. But,
On the retina corresponding to the area between the broken lines B and C, the amount of perception decreases, and the minimum value is almost zero. This decrease in the amount of perception is perceived as a false contour. The false contour is, as described above,
From gradation 128 in which only F8 emits light, SF7, SF
6, SF5, SF4, SF3, SF2, SF1, an image that changes to a gray level 127 at which light is emitted, that is, the digit is shifted down from the most significant bit to the lower bit, and conversely, the digit is shifted from the lower bit to the most significant bit. When a rising image moves on the screen, it is easily perceived. In addition, similarly to the case where the carry of the most significant bit and the carry of the lower bit occur, the false contour is perceived when the carry and the carry of the relatively higher bit occur.

[0022]

As described above, the conventional display device has a problem that the inverse gamma correction causes loss of gradation information in a low luminance area. Also,
If an image that changes smoothly from a higher bit to a lower bit in an image that changes smoothly, or vice versa, moves from a lower bit to a higher bit, the image is stationary. In this case, there is a problem that a false contour which cannot be seen is perceived.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides a display device that reduces loss of gradation information due to inverse gamma correction and reduces false contours in a moving image. With the goal.

[0024]

In a display device according to the present invention, a video signal of one field is converted into digital data, and a plurality of sub-displays having different relative ratios of display times corresponding to respective bits of the digital data are provided. In a display device that displays a halftone image by displaying or not displaying a field, the number of displayable tones is increased by adding a subfield having a relative ratio of display time that does not correspond to the digital data. In addition, there is provided means for converting the digital data into digital data having an increased number of tones when performing the inverse gamma correction conversion.

When a change in gradation to be displayed causes a carry or a borrow to a subfield having a relatively high display time relative ratio, one or more subfields are displayed. Is provided so as to maintain the following.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A display device according to an embodiment of the present invention performs inverse gamma correction on digitized video data, the number of bits being larger than the number of bits required to represent the data before correction. Since the coding is performed using the subfield and the number of gradations after the inverse gamma correction is increased, the loss of the gradation information on the low luminance side due to the inverse gamma correction works.

Further, when carry-up or carry-down occurs in a subfield having a relatively high display time relative ratio, one or more subfields are controlled so as to maintain a display state, so that the change is smooth. In order to reduce false contours that occur when an image moves from a relatively high bit to a low bit in an image to be processed, or vice versa, an image moves from a low bit to a relatively high bit. Work on.

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments. Embodiment 1 FIG. FIG. 1 is a block diagram of a driving device for a plasma display panel according to Embodiment 1 of the present invention. In the figure, 1 is an input terminal for inputting a video signal, 2
Is an input terminal for inputting a synchronization signal, 3 is an A / D converter for converting a video signal input to the input terminal 1 into a digital signal, and 4 is a code converter for converting the output signal of the A / D converter 3 5 is a frame memory for storing two frames of the output signal of the code converter 4, and 6 is a frame memory 5
And a driving unit that drives the display unit 7 by an output signal of a control unit 8 described later, 7 is a display unit such as a PDP driven by an output signal of the driving unit 6, and 8 is a synchronizing signal input to the input terminal 2. The control unit controls the A / D conversion unit 3, the code conversion unit 4, the frame memory unit 5, and the driving unit 6 as a reference.

FIG. 2 is a diagram showing an example of a light emission sequence in one field period in the driving device of the plasma display panel according to the first embodiment of the present invention. In the figure, SF9, SF8, SF7, SF6, SF5, S
F4, SF3, SF2, and SF1 each represent a subfield, and one field is composed of nine subfields. The relative ratio of the light emission time of each subfield is SF9, SF8, SF7, SF6, SF5, S
128: 96: 6 in the order of F4, SF3, SF2, SF1
4: 32: 16: 8: 4: 2: 1. By combining light emission and non-light emission in these subfields, 352
The halftone that has the gradation display capability of gradation and is expressed is determined by the sum of the relative ratios of the light emission times. 25 shown in FIG.
As compared with the light emission sequence of the conventional display having six gradations, SF8 having a light emission time of 96 is added in FIG.

Next, the operation will be described. The control unit 8
From the synchronization signal input to the input terminal 2, a predetermined control signal is output to each of the A / D converter 3, the code converter 4, the frame memory 5, and the driver 6. Input terminal 1
The video signal input from is converted by the A / D converter 3 into 8-bit digital data. The 8-bit digital data is converted into a 9-bit code by the code converter 4 as shown in Tables 3 and 4.

[0031]

[Table 3]

[0032]

[Table 4]

Here, the outputs of Tables 3 and 4 are obtained by converting the numerical values (0 to 351) of the output data such that the inverse gamma correction is performed from the numerical values (0 to 255) of the input data of 8 bits.
, 128, 96, 64, 32, 16,
This is represented by a combination of bits 8, 4, 2, and 1.

[0034]

(Equation 1)

Equation 1 is a calculation formula used in the code conversion of the present invention, x is a numerical expression of the input data of the code conversion unit 4, and y is a numerical expression of the output data when the input is x. It is. M is the number of gradations of digital data, and in this embodiment, M = 256. N is the number of gradations that can be expressed by the light emission sequence of the present invention, and in this embodiment, N = 352. γ is an inverse gamma coefficient, for example, γ = 2.2 is used. That is, in Tables 3 and 4, the gray scale is converted from 256 gray scales to 352 gray scales, and the inverse gamma correction is performed at the same time.

The code-converted data is stored by the control unit 8 in a predetermined position of the frame memory unit 5 for two frames. The frame memory unit 5 has a two-frame memory, and input data is alternately written to the first-frame memory and the second-frame memory for each frame.

The data stored in the frame memory unit 5 is read out from the frame memory unit 5 by the control unit 8 during the address period of SF9 shown in FIG. In this case, the data is read out of the two frame memories of the frame memory unit 5 from which data has not been written. The read data is output to the display unit 7 through the drive unit 6. After all the data of bit 9 for one frame is written in the display unit 7, the display unit 7 emits light only from the predetermined pixels corresponding to the bit 9 in the sustain discharge period of SF9 by the driving unit 6.

In the next SF8 address period, bit 8
Is read from the frame memory unit 5 and written into the display unit 7 through the drive unit 6. The display unit 7 is SF8
During the sustain discharge period, light emission is performed in the same manner as in SF9.

Hereinafter, similarly, SF7, SF6, SF5, S
In the order of F4, SF3, SF2, SF1, bit 7, bit 6, bit 5,
Bit 4, bit 3, bit 2, and bit 1 are read from the frame memory unit 5 in each address period, output to the display unit 7 through the drive unit 6, and correspond to data output in each sustain discharge period. To emit light.

In the display device configured as described above, the code conversion section 4 performs inverse gamma correction on the digital data as shown in Equation 1, and the digital data is larger than the gradation of the data output from the A / D conversion section 3. Since the conversion result is represented by the gradation (352 gradations) and encoded, the loss of the gradation information in the low luminance area due to the inverse gamma correction is reduced. This will be described with reference to FIG. FIG. 3 shows the inverse gamma correction using Tables 3 and 4 in Embodiment 1 of the present invention and the inverse gamma correction using Tables 1 and 2 in a conventional 256-gradation display device. 3A is an overall view, and FIG. 3B is an enlarged view of a low luminance area. As can be seen from the figure, the gradation expression in the low luminance region is improved as compared with the conventional 256 gradation display device. Here, as an example, M = 256 and N = 352 in Equation 1, but the present invention is not limited to this. In general, when N> M, the gradation expression can be improved.

Embodiment 2 In the display device configured as in the first embodiment, by appropriately selecting the code conversion in the code conversion unit 4, the gradation expression in the low luminance area is improved, and the false contour of the moving image is reduced. Can be configured. Hereinafter, such a second embodiment will be described.

Tables 5 and 6 are code conversion tables according to the second embodiment of the present invention, which are binary representations of patterns when coding gradation 0 to gradation 351 with 9 bits.

[0043]

[Table 5]

[0044]

[Table 6]

In Tables 5 and 6, the output value is gradation 9
6 and the gradation 255, Tables 3 and 4
Although the pattern is different from the above, the total of the light emission times is the same, and the luminance is the same as in the case of Tables 3 and 4.
Therefore, similarly to the first embodiment, the gradation expression in the low luminance region can be improved. In the patterns of Tables 5 and 6, SF8 always emits light when the gradation is 96 or more. Therefore, in this embodiment,
It is possible to reduce a false contour of a moving image at an intermediate gradation. This will be described with reference to FIG.

FIG. 4 is a diagram showing the state of carry of an image according to the second embodiment. Light emission when an image whose gradation is smoothly changed in the horizontal direction is displayed on the display of the present invention. It shows the state of. In the figure, the gradation after the inverse gamma conversion has changed from 223 to 224.

FIG. 5 is a diagram for explaining the effect of reducing false contours of a moving image according to the second embodiment. The image shown in FIG. 4 moves rightward at a speed of one pixel per field in the horizontal direction. It shows the state where it is. In the figure, the portion of the gradation 223 is the subfield SF8, SF7, SF6, SF
5, SF4, SF3, SF2, SF1 emit light,
At the gradation 224, the subfields SF9 and SF8 emit light. In the change from gradation 224 to gradation 223, SF9
SF8 continues to emit light, although a borrow from the subfield to the lower subfield has occurred.

When a human looks at an image displayed in such a pattern, the line of sight moves along with the movement of the moving image on the screen, so that the line of sight moves approximately on the broken lines indicated by A to D. . Here, on the retina, the amount of perception decreases at positions B to C, and this decrease in perception is recognized as a false contour. However, since SF8 continues to emit light, the decrease in the amount of perception is reduced, and the false contour is reduced.

As described above, according to this embodiment,
In a region where the luminance value after the inverse gamma conversion is equal to or more than the intermediate luminance of 96 or more, the false contour of the moving image is reduced.

The A / D converter 3 is not limited to the above example.
By using a light emission sequence using a larger number of subfields than the number of bits of the code, the code conversion unit 4 performs code conversion so that at least one subfield is always in a display state at a certain luminance value or more. The false contour of the moving image can be reduced in an intermediate luminance region equal to or higher than a certain luminance.

[0051]

Since the present invention is configured as described above, it has the following effects.

By increasing the number of gradations by the added subfield, gradation expression in a low luminance area can be improved.

By coding so that the added subfield always emits light in the middle part of the gradation, the false contour of the moving image at the middle gradation can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a light emission sequence in one field period in the first embodiment.

FIG. 3 is a diagram illustrating an effect of the first embodiment.

FIG. 4 is a diagram showing a state of carry of an image according to the second embodiment of the present invention;

FIG. 5 is a diagram for explaining a moving image false contour reduction effect according to the second embodiment;

FIG. 6 is a diagram showing an example of a light emission sequence in a conventional display device.

FIG. 7 is a block diagram showing a conventional display device.

FIG. 8 is a diagram showing a state of a carry of an image in a conventional display device.

FIG. 9 is a diagram for explaining a false contour phenomenon in a conventional display device.

[Explanation of symbols]

1 video signal input terminal, 2 sync signal input terminal, 3
A / D conversion section, 4 code conversion section, 5 frame memory section, 6 drive section, 7 display section, 8 control section.

Claims (2)

[Claims] 1. A video signal of one field is converted into digital data, the digital data is inversely gamma-corrected, and a plurality of sub-pixels each having a relative ratio of a different display time corresponding to each bit of the digital data after the inverse gamma correction. In a display device for displaying a halftone image by displaying or not displaying a field, one or more subfields having a relative ratio not corresponding to the digital data after the inverse gamma correction are added, and the added subfield is included. When displaying a halftone image by displaying or not displaying all subfields, the number of tones of digital data after inverse gamma correction is larger than the number of tones of the digital data simultaneously with inverse gamma correction. And a means for performing code conversion. 2. A display device comprising: means for controlling the added subfield to always maintain a display state when displaying a gradation requiring a display time longer than a relative ratio of the display time of the added subfield. Claim 1 characterized by the following:
The display device according to any one of the preceding claims.