JPH07264515A - Method for displaying gradation - Google Patents

Abstract

PURPOSE:To quiet a false image at the time of displaying an animation having a brightness difference based on the intermediate gradation of a television image or the like displayed on a plasma display panel or the like and to prevent the generation of flickers even on a screen having medium brightness. CONSTITUTION:A video signal 1 is converted into a digital signal consisting of required bits by an A/D conversion part 2 and the digital signal is recorded in a frame memory 3 in each field. The data in the memory 3 are inputted to a sub-field generating part 4 and plural sub-fields(SFs) in which the relative rates of luminance is binarily different are formed so that the brightest SF is arranged on the center and succeeding SFs are successively and alternately arranged on respective sides of the brightest SF in the descending order of brightness to constitute a 1st field and a 2nd field is constituted by arranging SFs in the reverse order of the 1st field. Two SF signals are alternately switched through a driving part 5 and displayed on a plasma display panel(PDP) 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation display method,
The present invention relates to a DP (Plasma Display Panel), a ferroelectric liquid crystal display body, or the like, which improves the image quality when displaying a moving image with an intermediate gradation such as a television image.

[0002]

2. Description of the Related Art A display device using a PDP or a ferroelectric liquid crystal element cannot display an image having a brightness gradation corresponding to an input signal because the drive input voltage and the display output show non-linear characteristics. . Therefore, the lighting period is subdivided, and the gradation is displayed depending on whether each lighting period is turned on or not, that is, the number of times of lighting is large or small. Therefore, for example, one field is configured by a plurality of subfields having different relative ratios of the lighting period (proportional to luminance),
The video signal is converted into a digital signal having the number of bits corresponding to the number of subfields in one field, and based on the bit data, an appropriate subfield (one subfield or a plurality of subfields) is turned on to turn on the corresponding pixel. Display a tonal image. By the way,
For example, when the relative ratio of the brightness of the subfields is arranged in ascending order, on a screen where a slightly bright image moves in front of a slightly dark background, a dark band-like false contour is formed on the edge of the slightly bright image in the traveling direction side. Can be seen. In this phenomenon, when a slightly dark image moves in front of a slightly light background, a bright strip-shaped dark portion is visible at the edge of the dark image in the traveling direction.

This phenomenon will be described with reference to the example shown in FIG. This figure shows a medium brightness image (sixth subfield = SF
6 is lit) is for advancing to the right one pixel in one field in front of a dark background (only SF2 is lit). In the first field (1F), the right edge of the bright image (SF6) is the position of pixel "1". In the next second field (2F), the pixel moves to the position of the pixel “2”, but the pixel of “2” of 2F does not light for a long period from lighting in SF2 of 1F to SF6 of 2F. Therefore, the afterglow of SF2 of 1F is lost during this period, and it is visible to the human eye as a dark image (ellipse 21 with a dotted line). The dark portion 21 becomes a pixel position of "3" in 3F, a pixel position of "4" in 4F, ..., and the dark portion 21 is temporally continuous according to the movement of the image. Since the human eye is sensitive to the difference between light and darkness adjacent to the movement of an image, when the bright image moves in front of a dark background, the above-mentioned continuous dark portion 21 (false image) is seen at the right end of the bright image. Originally, the boundary of the image can be recognized by the difference in brightness.When the difference in brightness is large, the false image is less noticeable due to the difference in brightness between the boundaries, but when the image in which the brightness changes slowly moves. It is visible, and the image quality is significantly impaired.

In order to eliminate this false image, a field in which the relative ratio of the luminance of the subfields is arranged in an ascending order and a field in which the relative ratio of the luminance of the subfields is arranged in a descending order are formed. The fields are displayed alternately, so that in one field, a striped dark portion at the edge of the bright image in the traveling direction and in the other field at the striped bright portion at the edge of the dark image in the traveling direction are displayed. Are alternated in the two fields, and the light and dark are averaged to make the false image less noticeable. However, in this case, for example, in an image of medium brightness in which only SF6 is lit, as shown in FIG. 6, a deviation of the lighting period occurs between adjacent fields,
A bright image with a repetitive period of 30 hertz is displayed once in two fields, which may cause a flicker phenomenon.

[0005]

As described above, according to the present invention, when a bright (dark) image moves in front of a dark (light) background, dark (dark) occurs at the edge of the bright (dark) image in the traveling direction. This is to prevent continuous (bright) portions from appearing, to prevent human eyes from seeing false images, and to prevent flicker in images of medium brightness.

[0006]

In order to solve the above-mentioned problems, the present invention forms a multi-gradation video signal by forming one field from a first sub-field to an n-th sub-field having a binary relative luminance ratio. In the display device adapted to display the, the first field is centered on the n-th sub-field having the highest relative luminance ratio, and
Each sub-field below the sub-field is alternately arranged before and after the n-th sub-field, and the second field is formed by arranging the sub-fields in a reverse order to the first field. It is intended to provide a gradation display method in which a first field and a second field are alternately switched and displayed.

[0007]

With the above-described structure, in the gradation display method according to the present invention, when a bright (dark) image moves in front of a dark (bright) background, the bright (dark) image is displayed at the edge in the traveling direction. The resulting dark (bright) striped edges, or false images, are averaged out in two fields that are scanned alternately, with the striped edges brightening and darkening, making the false images less noticeable and moderate. Brightness image, for example,
No flicker occurs even in an image in which only SF6 lights up.

[0008]

Embodiments of the gradation display method according to the present invention will be described in detail below. FIG. 1 is a block diagram of essential parts of an embodiment of a gradation display method according to the present invention. In the figure, 2 is A /
In the D converter, the analog video signal 1 is converted into a digital signal of 6 bits when the number of bits corresponding to the number of subfields, that is, when the number of subfields is 6, for example. A frame memory 3 records one frame of the digitally converted video signal. Reference numeral 4 denotes a subfield generation unit, which is based on the first bit data read from the frame memory 3, the first subfield (SF1), based on the second bit data SF2, ... Based on the sixth bit data. Generate SF6. A driving unit 5 drives the PDP 6 on the basis of a signal from the subfield generation unit 4 and the like. In the first field, SF1, SF3, SF5, SF
Scan in the order of 6, SF4, SF2, SF in the second field
2, SF4, SF6, SF5, SF3, SF1 are sequentially scanned, and thereafter, these field scans are alternately repeated. Reference numeral 7 denotes a sync separator, which separates the sync signal from the video signal 1. Reference numeral 8 denotes a control unit, which controls each of the above-described units on the basis of the sync signal from the sync separation unit 7.

Next, the operation of the gradation display method according to the present invention will be described. As in the example shown in FIG. 2, one field is SF1.
~ SF6 consists of 6 sub-fields, each sub-field has an address period and sustain (lights)
It consists of a period. In the subfield generation unit 4, the relative luminance ratio is 1 (SF1): 2 (SF2): based on the 6-bit video signal read from the frame memory 3.
6 of 4 (SF3): 8 (SF4): 16 (SF5): 32 (SF6)
It is generated in the sub-field, and for example, SF1, SF3, SF5, SF6 in the first field (a = first field),
SF4, SF2 in that order, that is, SF with the highest relative brightness ratio
SF5 or less, which has the second highest relative brightness ratio around 6
They are arranged alternately before and after SF6, and the next field (B
In the second field), they are arranged in the reverse order of the first field, and the signals of the fields (a) and (b) are alternately output and displayed on the PDP 6 via the drive unit 5.

In the address period of each sub-field, an address voltage is applied to the address electrode of the PDP 6 based on the display data read from the frame memory 3, whereby wall charges are formed in the corresponding cells. .
It should be noted that this wall charge is cleared at the end of scanning in the subfield and is formed in the next subfield based on the corresponding display data. Then, in the subsequent sustain (lighting) period, P is generated based on the required sustain pulse.
A sustain (lighting) voltage is applied to the sustain electrode of DP6, sustain discharge is performed in each cell, and display is performed.
This sustain discharge is discharged from the first sustain electrode to the second sustain electrode, and then from the second sustain electrode to the first sustain electrode. For example, in SF1, this sustain discharge is 4 cycles, 8 cycles in SF2, 16 cycles in SF3, 128 cycles in SF6. Since the amount of light emitted from the cells is proportional to the number of cycles of the sustain discharge, each cell displays an image with a gray scale corresponding to the gray scale of the video signal 1 by the sustain discharge at the required SF.

By configuring the field around SF6 as described above, the scanning cycle of SF6 substantially matches the field cycle, and for example, flicker on a screen of medium brightness in which only SF6 is lit is eliminated. To be done. This makes SF
On a dark screen in which only 1 or SF2 is lit, the brightness changes at a cycle twice as long as the field cycle, but since a flicker is less likely to occur on a dark screen, no problem occurs.

In addition, the above-mentioned SF is used in two consecutive fields.
Since the subfields before and after 6 are alternately switched, this causes the image of medium brightness (for example, only SF4 is lit) to have a slightly dark background (for example, only SF3 is lit, as in the example shown in FIG. 4). ) To the right one pixel in one field, the right end of SF4 is located at pixel "1" in 1F, and this right end is moved to pixel "2" in next 2F. The pixel of "2" of 1F is turned on 1 field after it is turned on by SF3 of 1F, so SF of 1F is turned on.
The afterglow of No. 3 is not lost, and the conventional dark image (fake image, = ellipse 21 of dotted line in FIG. 5) in the portion 11 shown by the dotted line is not seen.

In the above description, an example in which the PDP is used as the display body has been described, but the same applies to the case where a ferroelectric liquid crystal display body or the like is used. Further, in the above description, the video signal is converted into 6-bit digital data by the A / D conversion unit 2, but it is 8 bits or 8 bits depending on the processing speed of the display body.
You may make it process it after converting into digital data more than a bit. For example, in the case of processing with 8 bits, the subfield generation unit 4 configures each field with 8 subfields.

[0014]

As described above, according to the gradation display method of the present invention, the sub-field having the highest relative luminance ratio is centered, and the sub-field having the second highest relative luminance ratio is sequentially described above. The first field is formed by alternately arranging it before and after the subfield, and the second field is formed by arranging the subfield in a reverse order to the first field. Since the scanning is performed alternately, a screen with a medium brightness, for example, a screen in which only SF6 is turned on does not cause flicker because the scanning cycle of SF6 is substantially the same as the field cycle. In addition, a bright (dark) image when moving a field in front of a dark (bright) background, which is seen when a field is configured such that the relative ratio of the luminance of a conventional subfield is in ascending order, The striped dark (bright) false image that occurs at the leading edge of is canceled out by the two fields, and the display quality is improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an embodiment of a gradation display method according to the present invention.

FIG. 2 is an example of a driving sequence in the case of displaying a 6-bit digital video signal in 64 gradations.
Field (b) is the second field.

FIG. 3 is a conceptual diagram for explaining the positional relationship of SF6 in adjacent fields in the gradation display method according to the present invention.

FIG. 4 is a conceptual diagram showing a relationship between a lighting pixel and time for explaining a gradation display method according to the present invention.

FIG. 5 is a conceptual diagram for explaining a relationship between a conventional lit pixel and time.

FIG. 6 is a diagram illustrating a conventional gray scale display method in an adjacent field.
It is a conceptual diagram for explaining the positional relationship of SF6.

[Explanation of symbols]

 1 Video Signal 2 A / D Converter 3 Frame Memory 4 Subfield Generator 5 Driver 6 PDP (Plasma Display Panel) 7 Sync Separator 8 Controller F Field SF Subfield

Claims (3)

[Claims] 1. In a display device configured to display a multi-gradation video signal by forming one field from a plurality of subfields having different relative luminance ratios, the first field is set to the most of the relative luminance ratios. The subfields having the second highest relative luminance ratio and the subfields having the second highest relative luminance ratio with respect to the highest subfield are alternately arranged before and after the subfield having the highest relative luminance ratio.
And a subfield arranged in the reverse order of the first field, and the first field and the second field are alternately switched and displayed. 2. A first method having a binary relative brightness ratio
In a display device configured to display a multi-gradation video signal by forming one field from subfields to nth subfields, the first field is centered on the nth subfield having the highest relative luminance ratio. The n-th
Each subfield of 1 subfield or less is alternately arranged before and after the n-th subfield, and
And a subfield arranged in the reverse order of the first field, and the first field and the second field are alternately switched and displayed. 3. A first in which the relative ratio of luminance is binary different
In a display device in which one field is composed of subfields to sixth subfields to display a multi-gradation video signal, the first field is centered on the sixth subfield having the highest relative luminance ratio. Each of the sub-fields below the fifth sub-field is alternately arranged before and after the sixth sub-field, and the second field is formed by arranging the sub-fields in a reverse order to the first field. And a gradation display method in which the first field and the second field are alternately switched and displayed.