JP2002351390A - Display device and grey level display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the decrease of a display gray level by a simple method in the display of a PDP(plasma display panel), and to suppress the generation of the spurious profile of a moving picture. SOLUTION: The display period of one frame is divided into a lower-order subfield group for grey level displays in which light-emitting periods are weighted, and a high-order subfield group as an object for continuous light emitting in which the light-emitting periods are set, respectively. Then, the size of the level of inputted pixel data is compared with a threshold to determine whether it is low brightness or not. When it is low brightness, the lower- order subfield group is selected to display the grey level of the pixel. When it is high brightness, the high-order subfield group is continuously selected according to the high-order bits of pixel data, and whenever the number of subfields increases by one, the subfield having a short light-emitting period in the lower- order subfield group is selected according to the lower bits of the pixel data to display the grey level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a display device and a gradation display method for performing gradation display on a display panel such as a plasma display panel.

[0002]

2. Description of the Related Art Plasma display panels (hereinafter referred to as P
In the case of performing display on a display panel using DP) or a ferroelectric liquid crystal element, one frame display period (a period for displaying one screen: one field period) corresponding to 1/60 second is performed by a pixel lighting period. It is composed of a plurality of subfields having different relative ratios in a certain sustaining light emission period (proportional to light emission luminance).

FIG. 7 shows an example in which one frame display period is composed of eight subfields SF1 to SF8, and 256 grayscale bits are used to display 256 grayscales. That is, the uppermost gradation bit (the eighth bit) corresponds to the subfield SF1, the seventh gradation bit corresponds to the subfield SF2, and the sixth gradation bit corresponds to the subfield SF3. The fifth gradation bit is the subfield SF4, the fourth gradation bit is the subfield SF5, the third gradation bit is the subfield SF6, and the second gradation bit is the subfield SF4. The least significant gradation bit (first bit) corresponds to SF7, and corresponds to subfield SF8.

As described above, each of the subfields SF1 to SF
8, the sustained light emission period is 128 (= 2 ⁷ ), the number of gradations (relative ratio of light emission luminance: proportional to the number of sustained light emission pulses), respectively.
64 (= 2 ⁶ ), 32 (= 2 ⁵ ), 16 (= 2 ⁴ ), 8
(= 2 ³ ), 4 (= 2 ² ), 2 (= 2 ¹ ), 1 (= 2
⁰ ).

Here, each subfield SF1 to SF8
Has a scanning period in addition to the sustaining light emitting period. In the scanning period of the subfield SF1, the display data is written to each pixel of the PDP corresponding to the display data of the most significant bit (eighth bit). When the writing of the display data of the entire screen of the PDP is completed, P
A sustain light emission pulse is applied, for example, 128 times to the entire screen of the DP, and only the pixels for which writing has been performed emit light.

Next, in the scanning period of the subfield SF2, display data is written to each pixel corresponding to the display data of the seventh bit. When the writing of the entire screen of the PDP is completed, in the sustain emission period, a sustain emission pulse is applied to the entire screen of the PDP, for example, 64 times, and only the pixels for which the writing has been performed are caused to emit light. Hereinafter, in the subfields SF3, SF4, SF5, SF6, SF7, and SF8, display data is written to each pixel in the scanning period according to the display data of the corresponding bit.
When this is completed, in the next sustain emission period, the sustain emission pulse is applied 32 times, 16 times, 8 times, 4 times, 2 times, and 1 time, respectively, and only the pixels in which the writing has been performed are caused to emit light.

[0007]

As described above, in a display panel such as a PDP, a pixel has only two states, light emission and non-light emission. The frame display period is divided into a plurality of sub-fields, and weighting corresponding to the luminance level value of the display data is performed in each sub-field, and the corresponding pixel emits light with the number of times of light emission according to the weighting. Here, when the sustain emission period of each subfield is weighted as shown in FIG.
28, the light emission is performed only in the subfield SF1, and when the light emission is performed at the gradation number 127, the other subfields SF2 to SF2 except the subfield SF1 are emitted.
Light emission is performed in SF8. That is, during a period in which a pixel that should emit light at the gradation number 128 emits light in one frame display period, a pixel that should emit light at the gradation number 127 is in a non-light emitting state and emits light at the gradation number 127. During the period when the pixel to be lit emits light, the pixel to be lit at the gradation number 128 is in a non-light emitting state.

Therefore, if a pixel to emit light at the tone number 127 and a pixel to emit light at the tone number 128 are adjacent to each other, image quality degradation called a false contour of a moving image may occur in that area. .

In order to prevent such deterioration in image quality, Japanese Patent Laid-Open No. 2000-231362 proposes a driving method in which a subfield in one field is not inverted from non-light emission to light emission. That is, this driving method is 1
The frame display period is divided into N subfields, and consecutive M (2 ≦ M ≦ N) among the divided subfields
By controlling the light emission in each of the subfields, the pixels to emit light are caused to emit light continuously for a period corresponding to the luminance level, thereby suppressing the generation of the false contour of the moving image.

However, in the above-described driving method, since the display gradation becomes N + 1, the display gradation must be artificially increased by using a complicated method such as error diffusion.
There has been a demand for a simple method to suppress a decrease in display gradation and to suppress the occurrence of a false contour of a moving image. Therefore, an object of the present invention is to suppress a decrease in display gradation and a generation of a false contour of a moving image by a simple method when displaying a display panel such as a PDP.

[0011]

SUMMARY OF THE INVENTION In order to solve such a problem, the present invention provides a display panel such as a PDP in which a plurality of pixels are formed in a matrix. In a display device configured with a plurality of different subfields, each pixel of the display panel is displayed in multiple gradations by selecting a subfield of a light emission period according to the level of input pixel data and causing the pixels to emit light, One frame display period is divided into a lower subfield group (first subfield group) composed of a plurality of subfields each of which has a light emitting period weighted and used for gradation display of a pixel, and a pixel in which a light emitting period is set. Upper subfield group (second subfield) including a plurality of subfields used for continuous light emission of And a comparison between the level of the pixel data obtained by A / D conversion of the input video signal and a predetermined threshold value to judge whether the luminance is low or high. When a switching grayscale control unit for instructing grayscale switching according to the result and a grayscale switching instruction based on the low luminance determination result from the switching grayscale control unit are input, the level of the pixel data of the lower subfield group is reduced. While the corresponding subfield is selected to perform the gradation display of the pixel, when a gradation switching instruction based on the determination result of the high luminance is input from the switching gradation control unit, the subfield of the upper subfield group is set to the pixel data. Are successively selected according to the value of the upper bit of the lower subfield group, and when the number of subfields of the upper subfield group increases by one, the light emission period of each subfield of the lower subfield group is increased. Short subfield is a one provided with a light emission pattern control unit that performs gradation display of the selected pixel according to the value of the lower bits of the pixel data.

In this case, the light emission period of each subfield of the upper subfield group is set to be substantially the same. The light emission period of each subfield of the upper subfield group is set to increase linearly between the subfields. Further, the light emission period of each subfield of the upper subfield group is set so as to increase nonlinearly between the subfields. Also, among the subfields of the lower subfield group, each subfield except for the first subfield having the longest light emission time and the second subfield having the second largest light emission time is arranged in the order of shortest light emission time or long light emission time. In addition to the arrangement, one and the other of the first and second subfields are sequentially arranged following this arrangement.

The first subfield having the longest light emission time among the subfields of the lower subfield group is arranged at the center of the lower subfield group, and the other subfields are centered on the first subfield. Fields are arranged alternately before and after the first subfield in the order of longer light emission time. In addition, at least two consecutive subfields having a short light emission period among the subfields of the lower subfield group are arranged so as to be arranged in reverse order in the odd frame and the even frame. The switching gradation control unit calculates an average level of each pixel constituting one screen of the display panel, and sets a threshold value for determining whether the luminance is low or high based on the calculation result. is there.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. Generally, in a display device of a plasma display panel (hereinafter, PDP), one frame display period (one field period which is a display period of one screen) is divided into a plurality of subfields each of which has a sustained light emission period weighted. Input analog video signal to A
The digital data is converted into digital data having the number of bits corresponding to the number of subfields by D / D conversion, and the corresponding pixel of the PDP is caused to emit light by the subfield corresponding to the converted bit data to obtain an image of a predetermined gradation.

FIG. 1 is a block diagram showing a configuration of a display device of a PDP to which the present invention is applied. In FIG. 1, book P
The DP display device includes a PDP 8, an A / D conversion unit 1, a frame memory 2, a synchronization separation unit 3, a subfield configuration unit 4, a system clock generation unit 5, a light emission pattern control unit 6, a drive unit 7 and a switching gradation control unit 9.

Here, the A / D converter 1 converts the input analog video signal a into a number of bits corresponding to the number of subfields.
/ D conversion and output as digital video data. The frame memory 2 is A / D converted by the A / D converter 1.
The converted digital video data for one frame is stored. The synchronization separation unit 3 separates a synchronization signal from the analog video signal a. Switching gradation control section 9
Switches the gradation control between the low luminance part and the high luminance part, and determines the switching of the gradation control based on the statistical characteristics of luminance of one screen. The subfield forming unit 4 includes a switching gradation determined by the switching gradation control unit 9 based on the vertical synchronization signal of the synchronization separation unit 3 and a system clock generation unit 5.
The light emission period according to the relative ratio of the luminance of each subfield is determined using the internal clock generated in subfield S.
The timing from F1 to subfield SFn is determined. The light emission pattern control unit 6 selects a light emission pattern based on the timing control signal from the subfield construction unit 4 and outputs the light emission pattern to the drive unit 7. The driving unit 7 drives the PDP 8 based on the video data from the frame memory 2, the timing control signal from the subfield configuration unit 4, and the light emission pattern selected by the light emission pattern control unit 6, and includes a subfield SF1 The light emission operation from to is performed repeatedly.

(First Embodiment) FIG. 2 is a diagram showing a first embodiment of a PDP display device, showing the arrangement of subfields. In the present PDP display device, the display period of one frame is reduced by a timing control signal from the subfield forming unit 4 to a lower order composed of subfields having a short light emitting period (sustain light emitting period) as shown in FIGS. The subfield group is divided into a subfield group and an upper subfield group including subfields having a long light emission period, and each subfield SF of the lower subfield group is divided.
The emission times of 1, SF2, SF3, SF4, SF6 and SF6 are respectively set to 1 (= 2 ⁰ ),
2 (= 2 ¹ ), 4 (= 2 ² ), 8 (= 2 ³ ), 16 (=
2 ⁴ ), 32 (= 2 ⁵ )
Each subfield SF7-1 of the upper subfield group,
SF7-2, SF7-3, SF7-4, SF7-5, S
The light emission time of F7-6 is weighted as the same 32 (= ²⁵ ).

In the first embodiment, as shown in FIG. 2, a lower subfield group is arranged in the first half of one frame display period, and an upper subfield group is arranged in the latter half of one frame display period. I do. When arranging each subfield of the lower subfield group, the subfield SF1 having the shortest light emission time is arranged in ascending order (that is,
After the subfield SF4, the subfield SF6 is arranged after the subfield SF4, the subfield SF6 having the longest emission time is arranged, and then the subfield SF5 having the next longest emission time is arranged. Configure to be placed.

By arranging the subfields of the lower subfield group in this manner, the subfields of the lower subfield group are arranged in ascending order SF1, SF2, SF
3, the movement of the center of gravity in the gradation of the lower bits of the pixel data can be suppressed, and therefore, the false contour of the moving image can be reduced as compared with the case where the pixels are arranged like SF3, SF4, SF5.

FIG. 3 is a diagram for explaining an example of shifting the center of gravity during gradation display. Here, FIG. 3A shows that the light emission periods of the eight subfields SF1 to SF8 are binary codes of 1, 2, 4, 8, 16, 32, 64, and 128, respectively.
In this example, the subfields are weighted and arranged in descending order (that is, the subfields are arranged in descending order of the light emission period). In this case, in a state where the pixel level in a certain frame period A is 127 and gradation display is performed in all of the subfields SF1 to SF7, the pixel level becomes 128 in the next frame period B. Therefore, when the gradation display is performed only in the subfield SF8 due to the carry, as shown in FIG. The frame moves to the first half of the frame indicated by the code, and as a result, the luminance perceived by a human varies as shown in FIG. Note that FIG.
As shown in (c) and (d), each subfield SF1 to SF
The same applies to the case where 8 are arranged in ascending order.

For this reason, in this embodiment, FIG.
The above-described false contour of the moving image is reduced by optimizing the arrangement of the subfields as shown in (e) and (f), or by further dividing the subfields as shown in FIGS. I do.

In this manner, the subfield is divided and optimally arranged to suppress the shift of the center of gravity in the gradation of the lower bits of the pixel data, and furthermore, based on the information from the gradation switching control unit 9, the light emission pattern The control unit 6 outputs a light emission pattern shown in FIG. 4 to be described later to the drive unit 7 so as to perform gradation display, so that the subfields that emit light at the upper bits of the pixel data (each subfield SF7− of the upper subfield group). 1 to SF7-6) continuously increase, and it is also possible to suppress the shift of the center of gravity due to a rapid change in the light emission pattern that occurs when the gradation is carried. In addition, by controlling light emission / non-light emission of subfields corresponding to lower bits of pixel data (subfields of a lower subfield group) in correspondence with gradation, gradation can be expressed without noticeable false contours of moving images. .

FIG. 4 shows a first embodiment and a second embodiment to be described later.
FIG. 14 is a diagram showing an example of a light emission pattern which is also applied to the third embodiment and is output from the light emission pattern control unit 6 to the drive unit 7. This light emission pattern table indicates the correspondence between the input video level (level value of the A / D converted pixel data) and the selected subfield. , And a white circle in the figure indicates a subfield for which the selection of the selection is determined by the above-described switching gradation control unit 9.

The operation of the switching gradation control section 9 and the light emission pattern control section 6 will be described below with reference to FIG. The switching gradation control section 9 sets the video signal a to A by the A / D conversion section 1.
When the level value of the / D-converted pixel data is input, the information for selecting the light emission pattern of the table is determined according to the input level value, and the determined information is used as the gradation switching instruction information as the subfield configuration unit. 4 to the light emission pattern control unit 6. When the light emission pattern control unit 6 receives the gradation switching instruction information, the light emission pattern corresponding to the input information is selected from the light emission patterns in the table of FIG. 4 and output to the drive unit 7. The gradation display of the PDP 8 is performed by the selected light emitting pattern.

Here, the switching gradation control section 9 determines that the luminance value is low when the level value of the pixel data is "63" or less. In this case, the level value of the pixel data is directly used as the gradation switching instruction information as the light emission pattern control. By giving it to the unit 6, the light emission pattern control unit 6 selects the subfields corresponding to the video levels 1 to 63 in the table of FIG. 4 from the lower subfield group, and performs gradation display by the lower subfield group. Let

The switching gradation control section 9 determines that the luminance value is higher than "64" when the level value of the pixel data is "64" or more. Light emission pattern information such that all subfields of the field group emit light is provided to the light emission pattern control unit 6 as gradation switching instruction information, and the light emission pattern information is selected from the respective light emission patterns in the table of FIG. The light emitting pattern is selected and output to the drive unit 7. When the level value of the pixel data is in the range of 92 to 94, the switching gradation control unit 9 always emits light by the subfields SF3 to SF6 having the long light emission time of the lower subfield group, and sets the gradation digit. A constant sub-field SF with a new sub-field SF7-1 associated with the rise, and a sub-field SF with a short light-emission time for suppressing the shift of the center of gravity that occurs with the carry of the gradation.
Light emission pattern information for performing gradation display by light emission / non-light emission of SF1 and SF2 is given as gradation switching instruction information to the light emission pattern control unit 6, and the gradation switching instruction is selected from the light emission patterns in the table. The light emitting pattern corresponding to the information is selected and output to the drive unit 7.

When the level value of the pixel data is in the range of 95 to 119, the switching gradation control section 9 sets all subfields of the lower subfield group and subfield SF7 of the upper subfield group. Light emission pattern information that constantly emits light according to -1 is given to the light emission pattern control unit 6 as gradation switching instruction information, and a light emission pattern corresponding to the gradation switching instruction information is selected from the light emission patterns in the table. Then, the driving section 7 outputs the signal. Further, the switching gradation control unit 9 determines that the level value of the pixel data is 12
When it is within the range of 0 to 126, constant light emission by the subfields SF4 to SF6 having a long light emission time of the lower subfield group, constant light emission by the subfield SF7-1 of the upper subfield group, and carry-up of gradation The constant light emission by the new subfield SF7-2 associated with the above, and the gradation display by the light emission / non-light emission of the subfields SF1 to SF3 with a short light emission time for suppressing the shift of the center of gravity caused by the carry of the gradation. The light emission pattern information to be performed is given to the light emission pattern control unit 6 as gradation switching instruction information, and a light emission pattern corresponding to the gradation switching instruction information is selected from the light emission patterns in the table and output to the driving unit 7. Let it.

Hereinafter, the switching gradation control section 9 determines that the input level values of the pixels are 127 to 151, 159 to 183, respectively.
191 to 207 and 223 to 239, the light emission pattern control unit 6 sends SF1 to SF
7-2, SF1 to SF7-3, SF1 to SF7-4, and SF1 to SF7-4 are selected as all the subfields and light emission pattern information for constantly emitting light is given as gradation switching instruction information, and this gradation switching instruction is given. While the light emission pattern corresponding to the information is selected, the input level value of the pixel becomes 1
52-158, 184-190, 208-222 and 2
If the number is in the range of 40 to 254, the light emission pattern control unit 6 sets SF7-1 to SF7-3, SF7-3, SF7-3, and SF7-3 so that the number of each subfield of the upper subfield group increases by one.
SF7-1 to SF7-4, SF7-1 to SF7-5, and SF7-1 to SF7-6 are always selected to emit light, and a subfield having a long light emission time is selected from the lower subfield group to always emit light. Light emission pattern information for performing light emission and performing gradation display by light emission / non-light emission of a subfield having a short light emission time is given as gradation switch instruction information, and a light emission pattern corresponding to the gradation switch instruction information is selected. .

As described above, when the level value of the pixel is low luminance of "63" or less, the switching gradation control section 9 causes the light emission pattern control section 6 to select a sub-field corresponding to the level value from the lower sub-field group. A field is selected and output to the drive unit 7 to perform gradation display by light emission / non-light emission of each of the subfields SF1 to SF6. Further, the switching gradation control unit 9
Means that when the pixel level value is high luminance of “64” or more,
The light emission pattern control unit 6 selects a light emission pattern in which the number of subfields of the upper subfield group increases from the center to the rear half of the frame in accordance with the level value of the pixel data. At the time of carry-up of the gradation in which the sub-field increases by one, the sub-field having a short light-emission time is selected from the lower sub-field group to perform gradation display by light emission / non-light emission of these sub-fields. It is.

As a result, in the case of low luminance, the gradation can be expressed without making the false contour of the moving image conspicuous by the light emission / non-light emission of the subfields of the lower subfield group as described above. In the case of high luminance, the number of subfields SF7-1 to SF7-6 in the upper subfield group is continuously increased according to the pixel level value, and the number of subfields in the upper subfield group is one. At the time of increasing gradation carry, by the gradation display by light emission / non-light emission of the subfields having a short light emission time in the lower subfield group, the center of gravity shift accompanying the rapid change of the light emission pattern generated at the time of the gradation carry. Can be suppressed.

In the present PDP display device, the number of subfields in the lower subfield group is set to six subfields SF1 to SF6, and weighting is performed using a binary code. However, such a number of subfields is necessary. You may make it increase or decrease according to it. In the first embodiment, the subfields of the lower subfield group are arranged in the first half of the frame. However, they are arranged in the latter half of the frame in descending order (that is, in order from the one with the longest light emission period to the one with the shortest light emission period). Is also good. However, in this case, the subfield SF6 having the maximum light emission period is replaced with the subfield SF5 having the next longest light emission period, and the subfield is set to S.
They are arranged in the order of F5 → SF6 → SF4 → SF3 → SF2 → SF1. That is, when the lower subfield group is arranged in the first half of the frame and in the latter half of the frame, the arrangement of the subfields is symmetrical with respect to the center of the frame.

(Second Embodiment) FIG. 5 is a diagram showing a second embodiment of the PDP display device, and shows the arrangement of subfields. In the second embodiment, as in the first embodiment, the lower subfield group is arranged in the first half of one frame display period, and the upper subfield group is arranged in the latter half of one frame display period. . When each subfield of the lower subfield group is arranged, as shown in FIG. 5, the subfield SF6 having the longest light emission time is arranged at the center of the lower subfield group, and thereafter, with the subfield SF6 as the center. The sub-fields SF6 are alternately arranged before and after this sub-field SF6 in order from the sub-field having the long light emission period.

That is, with the subfield SF6 as the center, the subfield SFs are arranged in the direction of the start of the frame and in the direction of the upper subfield group in the order of longer light emission time.
5 and SF4, the subfields SF5 and SF4 are respectively followed by subfields SF5 and SF4.
3, SF2 is arranged, and finally subfield SF1 is arranged following subfield SF3. Therefore, each subfield of the lower subfield group is SF1 → SF
They are arranged in the order of 3 → SF5 → SF6 → SF4 → SF2.

As described above, each subfield of the lower subfield group is referred to as SF1 → SF3 → SF5 → SF6 → SF
By arranging in the order of 4 → SF2, it is possible to further suppress the shift of the center of gravity in the gradation of the lower bits, and therefore it is possible to further reduce the false contour of the moving image. Similar effects can be obtained by arranging the subfields of the lower subfield group in the order of SF2 → SF4 → SF6 → SF5 → SF3 → SF1 which is the reverse of the arrangement of FIG.

(Third Embodiment) FIG. 6 is a diagram showing a third embodiment of the PDP display device, showing the arrangement of subfields. In the third embodiment, as in the first embodiment, the lower subfield group is arranged in the first half of one frame display period, and the upper subfield group is arranged in the latter half of one frame display period. . Then, the subfields of the lower subfield group are arranged differently between adjacent odd and even fields.

That is, subfields SF5 and SF having a long light emission time among the subfields of the lower sub-yield group.
6 in the center of one frame display period,
As shown in FIG. 6A, in other odd-numbered frames, SF1, SF2, SF3, and SF4 are arranged in the order of short emission time (ascending order). As shown in FIG. 6 (b), SF4, SF3, SF2 and SF2 are arranged in descending order of the emission time.
It is arranged as SF1.

In this manner, by arranging the sub-fields SF1 to SF4 of the lower sub-field group having a short emission time between adjacent odd-numbered and even-numbered frames in reverse order, moving picture false contours in the gradation of the lower-order bit are eliminated. can do. Further, a subfield SF having a short light emission time is used.
By arranging 1 to SF4 in the first half of the frame, it is possible to eliminate an adverse effect on image quality such as flicker. In the third embodiment, the same effect can be obtained even if the lower subfield group is arranged in the latter half of the frame and the upper subfield group is arranged in the first half of the frame.

As in the first embodiment shown in FIG. 2, each subfield of the lower subfield group is SF1, SF
2, SF3, and SF4, the array is an array of odd fields, and the even fields of SF4, SF3, SF2, S
Similar effects can be obtained even when the arrangement is as shown in F1.

In the first to third embodiments, when the switching gradation control section 9 performs the switching gradation by determining the low luminance portion and the high luminance portion, the pixel level value is set to be less than "63" in advance. Is a low-luminance portion, and the switching gradation is performed with the level value “64” or higher as a high-luminance portion. However, the statistical value (1
A threshold may be set based on the average of the luminance levels of the respective pixels constituting the screen, and the switching gradation may be performed by determining whether the luminance is low or high according to the threshold.

In the first to third embodiments, the luminance level (light emission time) of each subfield of the subfield group of higher bits (higher subfield group) used in the high luminance section is fixed at "32". However, by changing these relative ratios, the false contour of the moving image can be more efficiently eliminated. That is, each subfield SF7-1 to SF7-6 of the upper subfield group used in the high luminance portion
The same effect can also be obtained by setting the luminance levels of, for example, 24, 28, 32, 36,... So as to linearly increase in order from SF 7-1. Also,
The luminance level of each of subfields SF7-1 to SF7-6 of the upper subfield group used in the high luminance section is represented by SF7-
For example, 24,2 so as to increase non-linearly from 1
By setting such as 7, 32, 33,..., The false contour of the moving image can be efficiently eliminated.

[0041]

As described above, according to the present invention, one frame display period of a display panel such as a PDP in which a plurality of pixels are formed in a matrix is constituted by a plurality of subfields in which the light emission periods of the pixels are different from each other. In a display device configured to perform multi-gradation display of each pixel of a display panel by selecting a subfield of a light emission period according to the level of input pixel data and causing the pixels to emit light, one frame display period A lower sub-field group composed of a plurality of sub-fields each of which has a light emission period weighted and used for gradation display of pixels, and a plurality of sub-fields each of which has a light emission period set and used for continuous light emission of pixels. It is divided into an upper subfield group and a switching gradation control unit and a light emission pattern control unit are provided. The switching gradation control unit compares the level of the pixel data obtained by A / D conversion of the input video signal with a predetermined threshold value to determine whether the luminance is low or high, and according to the determination result, When the light emission pattern control unit receives a gradation switching instruction based on the low luminance determination result from the switching gradation control unit, the light emission pattern control unit receives the gradation switching instruction from the switching gradation control unit. While selecting a field and performing gradation display of pixels, when a gradation switching instruction based on the determination result of high luminance is input from the switching gradation control unit, the subfields of the upper subfield group are set to the upper bits of the pixel data. The number of sub-fields in the upper sub-field group increases by one while the selection is continuously performed in accordance with the value, and if the number of sub-fields in the upper sub-field group increases by one, the sub-fields of the lower sub-field group in which the light emission period is short are reduced. Since the field is selected according to the value of the lower bit of the pixel data and the gradation display of the pixel is performed, when performing light emission display of each pixel of a display panel such as a PDP, a complicated method such as error diffusion is used. Thus, the generation of false contours of a moving image can be suppressed by a simple method without reducing the display gradation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a PDP display device to which the present invention is applied.

FIG. 2 is a diagram showing a first arrangement configuration of subfields in the present PDP display device.

FIG. 3 is a diagram illustrating a shift in the center of gravity of gradation in a general PDP display device.

FIG. 4 is a diagram showing a light emission pattern in the present PDP display device.

FIG. 5 is a diagram showing a second arrangement configuration of subfields in the present PDP display device.

FIG. 6 is a diagram showing a third arrangement configuration of subfields in the present PDP display device.

FIG. 7 is a diagram showing an arrangement configuration of subfields in a conventional PDP display device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... A / D conversion part, 2 ... Frame memory, 3 ... Synchronization separation part, 4 ... Subfield construction part, 5 ... System clock generation part, 6 ... Emission pattern control part, 7 ... Drive part, 8 ...
PDP, 9 ... Switching gradation control section, SF1 to SF6, SF7
-1 to SF7-6 ... subfields.

Claims (16)

[Claims] 1. A display panel including a plasma display panel in which a plurality of pixels are formed in a matrix forms one frame display period by a plurality of subfields in which light emission periods of the pixels are different from each other. In a display device that performs multi-gradation display of each pixel of the display panel by selecting a subfield of a light emission period according to a level and causing the pixels to emit light, the one frame display period has a ratio of the light emission period. A first sub-field composed of a plurality of sub-fields each of which is set to be weighted and used for gradation display of the pixel;
And a second sub-field group including a plurality of sub-fields, each of which has a light emission period and is used for continuous light emission of the pixel, and the input video signal is A / D converted. A switching gray level control unit for determining whether the luminance is low or high by comparing the level of the level with a preset threshold value, and instructing the switching of the gray level in accordance with the determination result; When a tone switching instruction based on a low-luminance determination result is input from the tone control unit, a subfield corresponding to the level of the pixel data in the first subfield group is selected to perform tone display of the pixel. When a tone switching instruction based on the result of determination of high luminance is input from the switching tone control unit, the subfields of the second subfield group are changed according to the value of the upper bit of the pixel data. With continuously selected, the number of subfields of the second subfield group by the selecting is increased by one, the first
A light emission pattern control unit that selects a subfield having a short light emission period among the subfields of the subfield group according to the value of the lower bit of the pixel data and performs a gray scale display of the pixel. Display device. 2. The display device according to claim 1, wherein light emission periods of each subfield of the second subfield group are set to be substantially the same. 3. The display device according to claim 1, wherein a light emission period of each subfield of the second subfield group is set so as to increase linearly between the subfields. 4. The display device according to claim 1, wherein a light emission period of each subfield of the second subfield group is set to increase nonlinearly between the subfields. 5. The sub-field according to claim 1, wherein, of the sub-fields of the first sub-field group, a first sub-field having the longest luminous time and a second sub-field having the second longest luminous time are provided. Are arranged in ascending order of light emission time or in descending order of light emission time, and one and the other of the first and second subfields are sequentially arranged following this arrangement. 6. The first subfield group according to claim 1, wherein, among the subfields of the first subfield group, a first subfield having a longest light emission time is arranged at the center of the first subfield group. A display device, wherein one sub-field is centered, and other sub-fields are alternately arranged before and after the first sub-field in order of a long emission time. 7. The sub-field of claim 5, wherein at least two consecutive sub-fields of the first sub-field group, each of which has a short light-emission period, are arranged reversely in odd frames and even frames. A display device, comprising: 8. The switching gradation control unit according to claim 1, wherein the switching gradation control unit calculates an average level of each pixel constituting one screen of the display panel, and determines whether the luminance is low or high based on the calculation result. A display device for setting the threshold value. 9. A frame display period of a display panel including a plasma display panel in which a plurality of pixels are formed in a matrix is constituted by a plurality of subfields in which light emission periods of the pixels are different from each other, and the input pixel data is In a display device that performs multi-gradation display of each pixel of the display panel by selecting a subfield of a light emitting period according to a level and causing the pixels to emit light, the ratio of the light emitting period is one frame display period. A first sub-field composed of a plurality of sub-fields each of which is set to be weighted and used for gradation display of the pixel;
And a second sub-field group consisting of a plurality of sub-fields each having a light emission period and used for continuous light emission of the pixel.
And determining whether the luminance is low or high by comparing the level of the pixel data obtained by A / D conversion of the input video signal with a preset threshold value. A second step of instructing a key change, and a gradation switch based on the low luminance determination result is instructed by the processing of the second step, the level of the pixel data of the first subfield group is reduced. While selecting the corresponding subfield and performing the gradation display of the pixel, when the gradation switching based on the determination result of the high luminance is instructed by the processing of the second step, the second subfield group Are successively selected in accordance with the value of the upper bit of the pixel data, and when the number of subfields in the second subfield group increases by one, the first subfield is selected. And selecting a subfield having a short light emission period from each subfield of the field group in accordance with the value of the lower bit of the pixel data, and performing grayscale display of the pixel. Display method. 10. The gradation display method according to claim 9, further comprising a fourth step of setting each light emitting period of each subfield of the second subfield group to be substantially equal. 11. The floor according to claim 9, further comprising a fifth step of setting a light emission period of each subfield of the second subfield group to increase linearly between the subfields. Key display method. 12. The floor according to claim 9, further comprising a sixth step of setting a light emission period of each subfield of the second subfield group to increase nonlinearly between the subfields. Key display method. 13. The sub-field according to claim 9, wherein, of the sub-fields of the first sub-field group, a first sub-field having the longest luminous time and a second sub-field having the second longest luminous time are provided. And a seventh step of sequentially arranging one and the other of the first and second subfields following this arrangement. Method. 14. The first subfield group according to claim 9, wherein, among the subfields of the first subfield group, a first subfield having a longest light emission time is arranged at the center of the first subfield group. 8. A gradation display method comprising: an eighth step of alternately arranging another subfield before and after the first subfield in ascending order of light emission time with one subfield as a center. 15. The sub-field according to claim 13, wherein at least two consecutive sub-fields having a short light emission period among the respective sub-fields of the first sub-field group are arranged reversely in odd frames and even frames. And a ninth step of arranging the gray scales. 16. The processing according to claim 9, wherein the processing in the second step calculates an average level of each pixel constituting one screen of the display panel, and determines whether the brightness is low or high based on the calculation result. A tenth step of setting the threshold value to perform the gradation display.