JP2004177563A - Plasma display drive circuit - Google Patents

Abstract

A plasma display driving circuit capable of performing motion detection with a smaller storage capacity than a conventional example is provided.
A plasma display driving circuit according to the present invention is a circuit that divides one field into a plurality of subfields, and performs gradation expression by controlling lighting / non-lighting of light emission in each of the subfields. The signal conversion unit 1 that generates a lighting pattern used for lighting / non-lighting control of each subfield based on the gradient of the video signal and the change in the lighting pattern before and after are compared to determine whether the video is a still image or a moving image. And a pseudo contour processing unit that adjusts light emission and non-light emission of a predetermined subfield in the lighting pattern and performs pseudo contour suppression processing when detecting that the moving image is a moving image.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a plasma display driving circuit for driving a PDP (Plasma Display Panel).
[0002]
[Prior art]
2. Description of the Related Art In recent years, PDPs have been improved in image quality such as luminance and contrast, and have been widely used as large-screen flat displays.
In this PDP, a subfield method is generally used for controlling lighting of pixels in order to perform gradation expression in an AC type PDP.
[0003]
However, it is well known that the subfield method easily generates a pseudo contour in principle.
The generation of the pseudo contour will be briefly described with reference to FIGS.
In FIG. 4A, there is originally an address setting period for selecting a pixel to be lit, so that the sustain (lighting continuation) period is not continuous as shown in FIG. Omitted for clarification.
[0004]
In FIG. T, the sustain signals for driving each pixel in the sustain period of each subfield have the same intensity (pulse voltage) of each sustain signal, the same light emission amount per time, and the time width (pulse width) represents a gradation. Controlled for.
As a result, on the retina of the human eye, the intermittent light emission in FIG. 4A is temporally integrated, and is captured as the luminance state shown in FIG. 4B, so that the light emission time (the total value of the sustain period) is obtained. ) Is longer, the amount of integration increases accordingly, and the image looks brighter. Thereby, gradation expression by the subfield is performed.
Therefore, as shown in FIG. 4A, the luminance (vertical direction) of each sustain signal is the same for each subfield.
4A, 4B, and 4C, the horizontal axis represents time.
[0005]
As described above, even when the image is a still image, even when the image is a still image, even if the image is a still image, even if the light emission scheme is continuously repeated, even if the image is a gray scale 127 or a gray scale 128 or all other gray scales. Even if the light emission is intermittent, normal gradation control is performed by a temporal integration effect.
However, when the image is a moving image, the situation is different, as shown in FIG. 5, when the object A having 128 tones moves in the background of 127 tones, that is, when the leading edge B is shifted from 127 tones. When the object A (to the right) moves such that the gradation changes to 128 gradations and the trailing edge C changes from 128 gradations to 127 gradations, a pseudo contour occurs.
[0006]
That is, as shown in FIG. 4A, in the leading edge portion B where the light emission of the gradation 127 changes to the light emission of the gradation 128, the time (T2) during which the pixel does not emit light is from the gradation 127 to the gradation 127. Becomes longer than the time (T1) during which the pixel does not emit light when changing to.
For this reason, in the period of 3F (field) in FIG. 4B, the amount of stimulation on the retina significantly decreases during the time T2 as compared with the time T1, and as shown in FIG. As for the eye sensitivity, the luminance at the leading edge B where the gradation changes from the gradation 127 to the gradation 128 appears to be lower than the substantial gradation.
As a result, a dark portion (pseudo-contour) is generated at the front edge B of the moving object A.
[0007]
Conversely, in the trailing edge portion C, when changing from the gradation 128 to the gradation 127, the period during which substantially no light is emitted becomes very short (the light emission period is adjacent), so that the amount of retinal stimulation increases. As a result, the brightness appears to increase compared to the substantial gradation.
As described above, actually, the gray scale 128 and the gray scale 127 differ only by one gray scale, but are recognized by the human eye as a larger luminance difference as compared with the actual gray scale difference. Pseudo contours are generated, which is a factor of deteriorating the quality of a moving image.
[0008]
For this reason, as a method for preventing the occurrence of the false contour, there is a configuration in which the motion detection shown in FIG. 7 is used and the encoding method is adaptively switched in accordance with the detection result to compensate for the gradation of the moving image portion. (Non-Patent Document 1).
That is, the comparison unit 101 compares the pixel of the immediately preceding field stored in the memory 100 with the pixel of the input field, calculates a difference in pixel gradation, and when the difference is confirmed, It detects that the pixel has changed, and determines that it is a moving image.
[0009]
The gradation number control unit 102 converts the gradation of the input image into a gradation in which the light emission scheme is continuous as shown in FIG.
Then, in accordance with the control signal from the comparison unit 101, the switching unit 103 outputs the input gradation as it is to the driving circuit of the PDP in the case of a still image, and is converted by the gradation number control unit 102 in the case of a moving image. The gradient is output to the drive circuit of the PDP.
At this time, in order to recover the gradation in the moving image portion, image compensation such as forming an error diffusion loop using a counting circuit and a delay circuit is performed.
[0010]
[Non-patent document 1]
Isao Kawahara, Kunio Sekimoto, "Development of a method for suppressing false contours of moving images for high-definition PDPs", Proceedings of the 2000 Annual Conference of the Institute of Image Information and Television Engineers, pp. 369-370
[0011]
[Problems to be solved by the invention]
In the above-mentioned conventional example, since it is necessary to compare the images in each field unit, by detecting the light emission scheme of the pixel at the same position in the immediately preceding field (performing motion detection), the effect of suppressing the pseudo image can be reduced. Can be done
However, in the above-described conventional example, a storage capacity for storing a video signal (gradation) of one field is required for detecting a light emission scheme, and a storage element for satisfying the storage capacity needs to be mounted. There is.
[0012]
In recent years, the resolution and resolution of a display image on a display have been advanced, and the data amount of one field has increased, and the storage capacity needs to be increased accordingly.
The increase in the capacity of the storage element (memory) to be mounted directly causes an increase in product cost as compared with a product that does not perform a comparison process between fields. Further, in the conventional example, when performing motion detection, the effect can be obtained by suppressing the false contour by performing the motion detection in a plurality of fields instead of the motion detection between the preceding and following fields, but the necessary storage is required. The capacity will be further increased.
[0013]
The present invention has been made under such a background, and an object of the present invention is to provide a plasma display driving circuit capable of performing motion detection with a smaller storage capacity than a conventional example.
[0014]
[Means for Solving the Problems]
The plasma display driving circuit according to the present invention divides one field into a plurality of subfields, and inputs a video signal in a plasma display driving circuit which performs gradation expression by controlling light emission / non-lighting of each subfield. By comparing a change in the lighting pattern before and after the signal conversion unit that generates a lighting pattern used for lighting / non-lighting control of each of the subfields from the gradient of the subfield, the video is either a still image or a moving image. Is detected, and if it is detected that the moving image is a moving image, a pseudo contour processing unit (block conversion unit 2) that adjusts light emission and non-light emission of a predetermined subfield in the lighting pattern and performs pseudo contour suppression processing , A memory 3, a comparison unit 4, and a pattern control unit 5).
[0015]
In the plasma display driving circuit according to the present invention, the pseudo contour processing unit classifies the lighting pattern corresponding to each gradation into a plurality of blocks based on a predetermined rule, and the input gradation is classified into a block. A block conversion unit that outputs the block number of
The plasma display driving circuit according to the present invention is characterized in that the pseudo contour processing unit has a storage unit for storing the block number in correspondence with each pixel of one frame.
[0016]
In the plasma display driving circuit of the present invention, the pseudo contour processing unit compares a block number stored in the storage unit with a block number generated from an input video signal for each pixel, A comparison unit that performs a motion detection for determining whether or not the motion detection is performed.
In the plasma display driving circuit according to the present invention, the pseudo contour processing unit controls a light emission and a non-light emission of a subfield at a predetermined position in the field in accordance with a comparison result output from the comparison unit. It is characterized by having.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, as described in the related art, one field shown in FIG. 6 is divided into a plurality of subfields, and the light emission / non-lighting control of each of the subfields is performed to control the gradation of each pixel in the frame. The present invention relates to a plasma display driving circuit for performing expression.
The plasma display driving circuit according to the present invention relates to a plasma display driving circuit for an AC PDP. In particular, a lighting pattern of each gradation is divided into blocks according to a predetermined rule, and a change between the blocks, that is, a pseudo contour is generated. Is configured to detect only a change in the lighting pattern in which is likely to occur.
[0018]
Thus, the plasma display driving circuit of the present invention can detect whether or not the gradation of each pixel of the video signal has changed, i.e., detect the change of the gradation of the corresponding pixel of the preceding and following frame images. Is performed not by comparing the gradient itself but by comparing the block number including the gradient, so that the memory capacity for storing data for comparing each pixel of the frame image is significantly reduced as compared with the conventional example. Have been.
As described above, the plasma display driving circuit of the present invention performs motion detection on a pixel-by-pixel basis, adjusts the gradient of the detected pixel based on the result of the motion detection, and suppresses false contours in the frame image. (A false contour suppression process).
Here, when a change in the gradient (block number) is detected in a pixel within one frame, the pixel is regarded as a moving image portion assuming that a motion is detected, and the change in the gradient (block number) is detected in the pixel. Otherwise, the pixel becomes a still image part because no motion is detected.
[0019]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a plasma display driving circuit of the present invention.
In FIG. 1, a signal conversion unit 1 converts an input video signal into a gradation (display gradation) of each pixel of the video signal (for example, digital data of RGB (using three primary colors of red / green / blue)). ), A lighting pattern used for lighting / non-lighting control of each subfield is generated by a conversion process using a look-up table or the like.
[0020]
That is, the signal conversion unit 1 converts the gradation of each pixel of the input video signal into a lighting pattern shown in the table of FIG.
FIG. 2 shows the relationship between the actually displayed gray scale and the lighting pattern indicating the combination of the subfields to be lit when displaying 256 gray scales.
[0021]
That is, as shown in FIG. 2, the signal conversion unit 1 converts the gradation into a lighting pattern for controlling lighting / fire lighting by a combination of subfields having different lighting periods.
In FIG. 2, the gradation is set to be higher as the subfield number is larger.
[0022]
The block conversion unit 2 classifies the lighting pattern, which has been converted corresponding to the gradient of each pixel, into a plurality of blocks based on a predetermined rule, as shown in FIG. Then, for each lighting pattern, the block number of the block to which the lighting pattern belongs is output and the block number is stored in the memory 3 in association with each pixel.
For this reason, in the block converter 2, the lighting patterns are classified into a plurality of blocks, as shown in FIG. 2, based on the predetermined rule.
[0023]
For example, in the example of FIG. 2, in a lighting pattern indicating 256 gradations, a change point of a subfield having a high gradation is used as a division of each block.
That is, in FIG. 2, each lighting pattern is classified by a subfield having the longest lighting period (a subfield having a high gradation) in each of the subfields in the lighting state in the lighting pattern expressing the gradient. Block configuration is set.
[0024]
For this reason, in each lighting pattern of FIG. 2, the block 0 is composed of the gradations 0 and 1 in which the lighting up to the subfield number 1 is performed.
Block 1 is the one in which the subfield number 2 is turned on as the subfield having the highest gradation (gradations 2 and 3).
Block 2 is a subfield having a subfield number 3 as the subfield having the highest gradation (gradations 4 to 7).
[0025]
Block 3 is the one in which the subfield number 4 is lit as the subfield having the highest gradation (gradation 8 to 15).
The block 4 is the one in which the subfield number 5 is lit as the subfield having the highest gradation (gradations 16 to 31).
Block 5 is the one in which the subfield number 6 is lit as the subfield having the highest gradation (gradations 32 to 63).
[0026]
Block 6 is the one in which the subfield number 7 is lit as the subfield having the highest gradation (gradation 64 to 127).
Block 7 is the one in which the subfield number 8 is lit as the subfield having the highest gradation (gradation from 128 to 255).
[0027]
The above classification in FIG. 2 is an example, and which lighting pattern is used to divide each block, what is the range of the lighting pattern included in each block, and the number of blocks to classify the lighting pattern (classification) The number is determined arbitrarily depending on conditions such as the degree of pseudo contour suppression processing and resolution / gradation.
[0028]
The comparison unit 4 stores the block number of the lighting pattern of each pixel of a previously input frame (for example, the immediately preceding frame or every other frame) stored in the memory 3 and the input frame. And the block number of the lighting pattern generated from the video signal of each pixel is compared for each pixel to determine whether the gradient has changed (whether it is a moving image portion or a still image portion). The motion to be determined is detected.
[0029]
For example, when comparing the block number of the lighting pattern generated from the video signal of each pixel of the input frame with the immediately preceding frame stored in the memory 3, the comparing unit 4 compares each pixel of the previous and next frames. Since the block numbers are compared, the effect of the pseudo contour suppression processing is improved.
In addition, the comparison unit 4 outputs to the pattern control unit 5 a control signal for instructing a change in the gradient of each pixel in accordance with which block in the lighting pattern has been moved between blocks. .
[0030]
As shown in the timing chart of FIG. 3, the pattern control unit 5 adjusts the gradation of each pixel by the control signal corresponding to the comparison result of the comparison unit 4, and outputs the adjusted gradation to the PDP. Then, light emission and non-light emission of a subfield at a predetermined position in the field are controlled, and the PDP is driven to display an image.
[0031]
Next, an operation example of the plasma display driving circuit of the present invention will be described with reference to FIGS.
In the timing chart of FIG. 3, the vertical axis indicates luminance, the horizontal axis indicates time, and there is actually an address setting period before each subfield, but is omitted as in FIG. ing.
[0032]
The signal converter 1 converts the gradation of each pixel of the input video signal into a lighting pattern, and outputs the lighting pattern to the block converter 2.
For example, if the video signal is a digital signal of the RGB system and the three primary colors of red / green / blue are represented by 256 gradations, respectively, the data amount is 8 bits, and a 24-bit signal is input as a whole. Is done.
For this reason, the signal conversion unit 1 separates the RGB video signal input with 24 bits into 8 bits each of red, green, and blue, and uses the gradation of each primary color as a lighting pattern as a lighting pattern. Output to
[0033]
Then, the block converter 2 classifies the input lighting patterns of the three primary colors into blocks shown in FIG. 2 for each primary color.
Next, the block conversion unit 2 stores the block numbers of the blocks of each primary color classified for each lighting pattern in the memory 3 for each primary color, and outputs the block numbers of each primary color to the comparison unit 4.
Here, in FIG. 2, since the blocks are eight types of blocks 0 to 7, the block numbers of the respective primary colors can be represented by 3 bits, respectively. Therefore, the block conversion unit 2 stores the 9-bit block number data in the memory 3 And outputs it to the comparison unit 4.
[0034]
Thus, the comparison unit 4 independently compares the input lighting pattern and the lighting pattern of the immediately preceding frame read from the memory 3, that is, the block numbers of the preceding and succeeding fields, for each of the three primary colors.
At this time, every time the comparing unit 4 reads the block number of the lighting pattern for comparison from the memory 3 for every three primary colors, the block converting unit 2 sequentially overwrites the block number of the lighting pattern of the pixel at the corresponding position. Then, the block numbers of the converted lighting patterns are stored.
As a result, the content of the memory 3 stores the block number of the lighting pattern of each new frame every time the comparison is performed.
[0035]
Hereinafter, since the same operation is performed for each of the three primary colors, the type of the primary colors is not shown, but the same processing is performed for all the three primary colors.
For example, in the timing chart of FIG. 3, when shifting from the 2F (field) of the gradation 127 to the 3F of the gradation 128, even if the gradations are almost the same as described in the conventional example. When the non-lighting period is long, the gradation is low and is perceived by human eyes.
For this reason, it is necessary to prevent the gradation from decreasing and the substantial gradation from decreasing as shown in FIG. 4 (c), so that the front edge B of the object A in FIG. There is.
[0036]
Here, the comparison unit 4 compares the block number “block 6” of the memory 3 with the block number “block 7” output from the block conversion unit 2, and determines that the non-lighting period between fields is long. In other words, when it is detected that the gradation changes from block 6 (gradation 127) to block 7 (gradation 128), a predetermined position in the non-lighting subfields of the second and third floors is determined. A control signal for instructing a process of inserting a newly lit subfield into the lighting pattern so as to light the subfield is output to the pattern control unit 5.
[0037]
Thus, when shifting from the 2F (field) to the 3F, the pattern control unit 5 turns on any one of the subfields as a predetermined subfield between the subfields 1 to 7 (non-lighting). The gradation is adjusted so that Add Pulse (add pulse is inserted) during the period, the video signal (RGB image signal) of the adjusted gradation is output to the PDP, and the light emission of the subfield at a predetermined position in the field is performed. And control of non-emission, and drive the PDP to display an image.
[0038]
As a result, the sensitivity of the human eye is such that even when the gray level changes from the gray level 127 to the gray level 128, the presence of the subfield that is lit during the long non-lighting period causes the temporal integration of the human retina. In the present invention, it is possible to suppress the decrease in the stimulus amount, and to suppress the false contour without substantially lowering the gradation (lowering the luminance perceived by humans) as in the conventional example.
[0039]
On the other hand, in the timing chart of FIG. 3, when shifting from the 3F at the gradation 128 to the 4F at the gradation 127 (when the change in the gradation of the pixel is detected by the motion detection), the description is given in the conventional example. As described above, even when the non-lighting period is extremely short even if the gradations are almost the same, the gradation is high and can be felt by human eyes.
For this reason, it is necessary to prevent the stimulus amount due to the temporal integration from increasing and the substantial gradient (luminance perceived by a human) from increasing, so that the trailing edge C of the object A in FIG. There is.
[0040]
Here, the comparison unit 4 compares the block number “block 7” of the memory 3 with the block number “block 6” output from the block conversion unit 2, and the non-lighting period between fields is shorter than a predetermined period. In other words, when the gradation changes from block 7 (gradation 128) to block 6 (gradation 127), the sub-fields at the predetermined positions in the sub-fields of the lighting periods of the 3F and 4F are determined. A control signal for instructing the pattern control unit 5 to perform a process of thinning out the subfields to be lit from the lighting pattern (making one of the lit subfields to be fired) so that the field is turned off.
[0041]
Accordingly, when shifting from the third to fourth floors described above, the pattern control unit 5 performs a process of thinning out any one of the subfields between the subfields 1 to 7, and turns off a predetermined subfield, The gradation in the lighting pattern is adjusted, the video signal of the adjusted gradation is output to a PDP (not shown), and light emission and non-light emission of a subfield at a predetermined position in the field are controlled to drive the PDP. Then, an image is displayed.
[0042]
As a result, in the case where the sensitivity of the human eye changes from gradation 128 to gradation 127, there is a non-lighting sub-field in the sub-fields that are continuously lighted in a short non-lighting period between the lighting patterns. Therefore, it is possible to suppress an increase in the amount of stimulation on the human retina in temporal integration, and to suppress a pseudo contour in the present invention without substantially increasing the gradient as in the conventional example. It becomes.
[0043]
Further, as shown in FIG. 3, when the comparison unit 4 detects that the block number “block 6” has not been changed in the transition from the first floor to the second floor, that is, the comparison unit 4 determines that the pixel has no motion detected. Upon detection, a control signal indicating that the gradation adjustment is not performed is output to the pattern control unit 5.
As a result, the pattern control unit 5 outputs each pixel of the input video signal to the PDP with the same gradation without adjustment.
[0044]
By performing the above-described processing independently for all three primary colors, the gradations are close to the gradation 127 and the gradation 128, but due to the characteristics of the subfield method, the amount of stimulation on the human retina is small. A drastic change is made, and it becomes possible to suppress a false contour occurring in the human eye.
Note that the pattern conversion unit 2 and the comparison unit 4 arbitrarily perform processing in parallel with three primary colors separately based on the processing speed and the limitation of the circuit scale, or sequentially perform processing in time series with one circuit. Any of the circuit configurations can be used.
[0045]
As described above, the video signal used for the conventional motion detection is assumed to be 256 gradations (8 bits) (3 × 8 bits = 24 bits as a whole) as RGB data, and the resolution is set to VGA ( Video Graphics Array; 640 × 480)
24 (bits) x 640 x 480 = 7372800 (bits)
Requires a memory with a storage capacity of
[0046]
However, in the present invention, the number of blocks is eight (3 bits are required to identify eight types of blocks 0 to 7) as RGB data (3 × 3 bits = 9 bits in total). If the resolution is equivalent to VGA as in the conventional example,
9 (bits) x 640 x 480 = 2764800 (bits)
, Which is 37.5% of the memory capacity of the conventional example.
As a result, the plasma display driving circuit of the present invention can greatly reduce the capacity of the memory in the circuit for performing motion detection, and can reduce the cost of the entire circuit.
[0047]
In addition, the plasma display driving circuit of the present invention performs the motion detection in the comparison unit 4 by comparing the block numbers of the corresponding pixels in the preceding and succeeding frames (comparing the magnitudes of the blocks). It is possible to use the comparison result itself as a control signal without individually detecting a carry or a borrow in each bit unit of the bit pattern. That is, it is possible to simply and accurately adjust the insertion of the lighting subfield and the setting of the non-lighting subfield with respect to the gradation.
[0048]
【The invention's effect】
As described above, according to the present invention, when performing motion detection in suppressing a false contour, unlike the conventional motion detection method, it is necessary to use the difference in the gradient of the pixel at the corresponding position between the previous and next frames. In addition, since the motion detection is performed based on the block number of the block in which the lighting pattern is classified, it is not necessary to store the gradient for each pixel in a frame unit. It is possible to provide a plasma display drive circuit that performs the following.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of a plasma display driving circuit of the present invention.
FIG. 2 is an example of a table showing a block configuration in which a block converter 2 in FIG. 1 classifies each lighting pattern.
FIG. 3 is a timing chart showing an operation example of the plasma display drive circuit of FIG.
FIG. 4 is a timing chart showing an operation example of a conventional plasma display drive circuit.
FIG. 5 is a conceptual diagram showing a concept of generation of a pseudo contour in a moving image.
FIG. 6 is a conceptual diagram showing a field configuration of a subfield system.
FIG. 7 is a block diagram illustrating a configuration example of a conventional plasma display drive circuit.
FIG. 8 is a conceptual diagram showing a configuration of a lighting pattern of a subfield for explaining suppression of a pseudo contour according to a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Signal conversion part 2 Block conversion part 3 Memory 4 Comparison part 5 Pattern control part

Claims (5)

In a plasma display driving circuit that divides one field into a plurality of subfields and performs gradation expression by controlling light emission / non-lighting of each subfield,
A signal conversion unit that generates a lighting pattern used for lighting / non-lighting control of each of the subfields from a gradient of an input video signal;
By comparing the change of the lighting pattern before and after, whether the video is a still image or a moving image is detected, and when it is detected that the moving image is a moving image, a predetermined subfield of the lighting pattern is detected. A plasma display drive circuit, comprising: a pseudo contour processing unit that adjusts light emission and non-light emission and performs pseudo contour suppression processing. A block conversion unit configured to classify the lighting pattern corresponding to each gradient into a plurality of blocks based on a predetermined rule, and to output a block number of the block into which the input gradient is classified; The plasma display drive circuit according to claim 1, further comprising: 3. The plasma display drive circuit according to claim 2, wherein the pseudo contour processing unit has a storage unit that stores the block number in correspondence with each pixel of one frame. The pseudo contour processing unit compares the block number stored in the storage unit with a block number generated from an input video signal for each pixel, and performs motion detection to determine whether the image is a moving image. 4. The driving circuit according to claim 3, further comprising a comparison unit for performing the comparison. 2. The image processing apparatus according to claim 1, wherein the pseudo contour processing unit includes a pattern control unit that controls light emission and non-light emission of a subfield at a predetermined position in the field in accordance with a comparison result output from the comparison unit. 5. The plasma display driving circuit according to 4.

Images