JP3889020B2 - Image signal processing method and image signal processing apparatus - Google Patents

Description

  The present invention relates to an image signal processing method and an image signal processing device for reducing a moving image false contour generated in a display device using a subfield method such as a plasma display panel.

  As a conventional basic multi-gradation display method, for example, as described in FIG. 8 of Patent Document 1 (Japanese Patent Laid-Open No. 7-271325), one field of 64 gradations has a luminance ratio of 1: There is a method of combining six subfields arranged in the order of 2: 4: 8: 16: 32. In the six subfields, the lighting order for performing the sustain discharge operation is fixed, and the order is the same with respect to the time axis.

  However, when a moving image is expressed using this method, if a bit-up gradation (between 63 and 64, 31 and 32, 15 and 16, etc.) occurs, the temporal non-uniformity of light emission is significant, There was a problem that the gradation disturbance became large. Such a disturbance in gradation is called a moving image false contour.

  For this reason, in order to obtain a good image quality, it is necessary to specify a portion where such a moving image false contour occurs and to perform signal processing for reducing the moving image false contour at the specified portion.

  As a method for specifying a location where a false false contour occurs, image data for one field period is stored in the frame buffer, and the image data of the next field period is compared with the stored image data of the field period. There is a method of detecting a motion vector based on the comparison result.

Moreover, as a method for reducing the moving image false contour, for example, the following method described in FIGS.
(A) A method of changing the order of each subfield.
(B) A method of increasing the number of subfields divided in one field so that there are two or more combinations of subfields that are lit when displaying gradation.

  Furthermore, a method of spatially diffusing gradation disturbance by signal processing such as an error diffusion method is also employed.

  Furthermore, as another method for reducing the moving image false contour, there is a method called an equalization pulse method as described in Non-Patent Document 1 (Display and Imaging 1997, Vol. 5, pp. 229-240). is there. This equalization pulse method is to add extra light emission to the original signal when it is expected that gradation disturbance will be observed when the line of sight moves on a display that uses the subfield method. Or a method of reducing a large gradation fluctuation by subtracting a certain amount of light emission from the original signal.

JP 7-271325 A Display and Imaging 1997, Vol. 5, pp. 229-240

  However, the method of detecting a motion vector and identifying a location where a moving image false contour occurs requires a large-capacity frame buffer, and thus has a problem that the cost is remarkably increased. Further, it is practically impossible to detect a large number of motion vectors at a time, and it is difficult to detect a sudden and large change in motion vectors. As a result, erroneous detection is performed, and there is also a problem that the image is extremely deteriorated by the moving image false contour reduction processing based on the erroneous detection.

Further, the conventional moving image false contour reduction processing method for multi-gradation display has the following problems. First, if there are N subfields, 2 ^N gradations can be expressed, but in order to reduce temporal non-uniformity of light emission and reduce moving image false contours, subfields to be divided in a plasma display panel When the number is increased from N, the sustain discharge period is shortened and the luminance is lowered. For this reason, the number of subfields cannot be increased without lowering the luminance. Second, even when the number of divided subfields is increased, gradation disturbance at a specific gradation level occurs, and thus gradation disturbance at a specific gradation level cannot be prevented.

  Furthermore, the conventional moving image false contour reduction processing method using signal processing such as an error diffusion method has the following problems. First, since signal processing is performed on an input signal regardless of whether or not a moving image false contour occurs, input signals other than the region where the moving image false contour occurs are deteriorated. Second, since there is no regularity in the gradation disturbance diffused by the error diffusion method or the like, it is impossible to predict in advance the influence of the diffusion gradation disturbance.

  Furthermore, the moving image false contour reduction processing method using the equalization pulse method has the following problems. First, in order to reduce the disturbance of the image recognized by the eyes, the motion of the image is detected in the input signal and the signal is corrected according to the moving speed of the image. Since it may be worse, the video quality may be degraded by incorrect signal correction. Second, since it is assumed that the line of sight follows the moving image, when the line of sight does not follow the image, image distortion may be recognized by the corrected signal.

  The present invention has been made in view of such a problem, and provides an image signal processing method and an image signal processing apparatus capable of reducing deterioration in image quality due to a false contour of a moving image with a simple structure and process. With the goal.

According to the image signal processing method of the present invention, one field period is divided into a plurality of subfields having different relative luminance ratios, and the display device is configured to express gradation by combining the luminances of the respective subfields. In an image signal processing method for processing an image signal, by replacing pixel values of specific pixels among four pixels that are arranged in the display device in succession and whose pixel values are monotonously increasing or decreasing. And changing the gradation level arrangement to increase at least one of the total number of carry-ups and the total number of carry-downs of the subfields included in the gradation level arrangement.

  In the present invention, the generation areas of moving image false contours are dispersed and offset each other, so that deterioration in image quality due to moving image false contours can be reduced while suppressing deterioration in moving image quality.

  Therefore, it is preferable that the absolute value of the difference between the total number of carry and the total number of carry-down after the change of the array becomes 0 or 1 by the step of increasing at least one of the plurality of pixels. It is preferable that carry and carry appear alternately within the gradation level.

  Further, the step of increasing the at least one includes, for example, a step of exchanging each gradation level between two pixels. In this case, the two pixels are adjacent to each other. Since the area where the tone level is exchanged is narrowed, it is possible to minimize the degradation of the moving image quality.

An image signal processing apparatus according to the present invention divides one field period into a plurality of subfields having different relative luminance ratios, and causes a display device to express gradation by combining the luminances of the respective subfields. In an image signal processing apparatus that processes an image signal, by replacing the pixel values of specific pixels among four pixels that are arranged in succession on the display device and whose pixel values monotonously increase or decrease It has a pixel value changer that changes the arrangement of gradation levels and increases at least one of the total number of carry-ups and the total number of carry-downs of subfields included in the arrangement of gradation levels. .

In addition, the gradation level in the one field period smoothly changes between the four pixels arranged in succession on the display device, and the plurality of pixels in the one field period. Detecting a pixel including a carry or carry of at least one subfield in an array of gradation levels, or the one field period between two adjacent pixels included in the plurality of pixels the variation of the light emission time period of inner is further provided a detector for detecting a pixel equal to or greater than a predetermined value, the pixels which are detected by the detector array of gray level is changed by the pixel value replacement unit 4 By being included in each pixel, it is possible to efficiently reduce the moving image false contour with a simple configuration that does not require a frame buffer.

  The pixel value changer preferably sets the absolute value of the difference between the total number of carry and the total number of carry after the arrangement change to 0 or 1, and the gradation of the plurality of pixels. Preferably, carry and carry appear alternately within the level.

  In addition, the pixel value changer preferably exchanges each gradation level between two pixels, for example, and in this case, the two pixels are preferably adjacent to each other.

  Furthermore, based on the motion detection circuit that detects the motion of the image by comparing the image signal of the one field period and the image signal of the one field period immediately before or immediately after the image signal, and both output signals of the detector and the motion detection circuit And a second detector that determines whether or not the array value is changed by the pixel value changer, thereby enabling detection of a motion vector and more appropriately determining a pixel that is assumed to generate a moving image false contour. It becomes possible to specially make it possible to reduce the moving image false contour while further suppressing the deterioration of the image quality.

In the specification of the present application, the carry represents the gradation level of a pixel that passes first between adjacent pixels in the direction in which the line of sight moves, regardless of the arrangement order of subfields within one field period. One or more subfields (first subfield group) that emit light for the purpose, and one or more subfields (second subfield group) that emit light to express the gradation level of the pixel that passes through A case where the following two relations are satisfied.
(A) Among the first subfield groups, either the subfield having the highest weight or the subfield one level lower than that is not included in the second subfield group.
(B) The subfield higher in weight than the subfield having the highest weight in the first subfield group is included in the second subfield group.

  On the other hand, the carry-down refers to a case where the reverse relationship of (a) and (b) holds regardless of the arrangement order of subfields within one field period. Therefore, when a carry occurs when the line of sight moves in one direction, there is a relationship that a carry occurs when the line of sight moves in the opposite direction.

  According to the image signal processing method or the image signal processing apparatus according to the present invention, it is possible to disperse the moving image false contour by changing the gradation level. Therefore, it is possible to suppress a decrease in image quality due to the moving image false contour.

  Hereinafter, an image signal processing apparatus according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an image signal processing apparatus according to the first embodiment of the present invention.

  In the first embodiment, a moving image false contour detector 10 that detects a pixel assumed to generate a moving image false contour from image data for one field period, and pixels specified by the moving image false contour detector 10 On the other hand, a pixel value changer 20 for changing the pixel value is provided. Further, a look-up table LUT (not shown) that can be referred to from the moving image false contour detector 10 and the pixel value changer 20 and records the relationship between each gradation level and light emission / non-light emission of the subfield is provided. It has been. FIG. 2 shows the contents of the lookup table LUT. FIG. 2 shows an example of the light emission / non-light emission state of the subfield when each gradation level is expressed in the case where 32 gradations are expressed with the number of subfields being five. As shown in FIG. 2, SF1, SF2,..., SF5 are sequentially set from the top in the region where one field is divided into five subfields, and the ratio of the light emission periods of the respective regions is 1: 2: 4: 8: 16. And In FIG. 2, the state in which the subfield emits light is represented by ●.

  Next, the moving image false contour detector 10 will be described. FIG. 4 is a block diagram showing a configuration of the moving image false contour detector 10. For example, the pixel value (gradation level) P (i, j) of the image A (i, j) in the i-th column from the left and the j-th row from the top of the display device is input to the moving image false contour detector 10. A carry / carry-down discriminator 11, a monotonicity discriminator 12, and a contour detector 13 are provided. In the present specification, unless otherwise specified, the numbers and positions of rows and columns indicate those in pixels emitting the same color.

  The carry / carry-down discriminator 11 includes not only the pixel value P (i, j) of the image A (i, j) but also the pixels A (i + 1, j) and A (i + 2, j) that are continuous in the same row. And each pixel value P (i + 1, j), P (i + 2, j) and P (i + 3, j) of A (i + 3, j) is also stored and created based on the lookup table LUT shown in FIG. With reference to the carry / carry-down discrimination table (FIG. 3), when there are those defined in the carry / carry-down discrimination table among these four types of pixel values, the image A (i, j The output signal OUT1 for the image A (i, j) is low when the output signal OUT1 for the image A (i) is not present.

  The carry / carry-down discrimination table defines that the sub-fields that emit light are compared between adjacent pixels to satisfy the following condition. That is, any one of the subfield with the highest weight or one subordinate subfield among the one or a plurality of subfields (higher subfield group) that emit light to express the higher gradation level. In order to express a lower gradation level, it is required that the light emission is not included in one or a plurality of subfields (lower subfield group) that emit light.

  For example, for the gradation level 15 and the gradation level 16, the subfields SF3 and SF4 for expressing the gradation level 15 are not included in the subfield for expressing the gradation level 16, and more than that. Since the upper subfield SF5 is selected and emits light when expressing the gradation level 16, a continuous arrangement of the gradation level 15 and the gradation level 16 is defined in the carry / carry determination table. . For the gradation level 15 and the gradation level 24, the subfield SF3 for expressing the gradation level 15 is not included in the subfield for expressing the gradation level 24, and the gradation level 15 is Since the subfield SF5 higher than the uppermost subfield SF4 for expression is selected and emits light when expressing the gradation level 24, the continuous arrangement of the gradation level 15 and the gradation level 24 is also carried. / Defined in the carry-down discrimination table.

  On the other hand, for the gradation level 24 and the gradation level 31, since the subfields SF4 and SF5 for expressing the gradation level 24 express the gradation level 31, the gradation level 24 and the gradation level 31 are continuous. This arrangement is not defined in the carry / carry determination table.

  In other words, in the arrangement defined in the carry / carry-down discrimination table, the light emission / non-light emission state of the subfield is reversed between two consecutive gradation levels, and the temporal distribution of light emission is greatly different. is there. When the line of sight passes through a pixel having such a relationship that the light emission time zone is inverted, it is recognized that the gradation is disturbed, and a false contour is generated.

  For subfields having weights lower than a predetermined value, for example, subfields SF1 and SF2 having a weight of 2 or less, the arrangement defined in the carry / carriage determination table is determined without considering the presence or absence of light emission. May be.

  As with the carry / carry-down discriminator 11, for example, the monotonicity discriminator 12 not only includes the pixel value P (i, j) of the image A (i, j) but also the pixels A (i + 1, continuous in the same row. j), the pixel values P (i + 1, j), P (i + 2, j) and P (i + 3, j) of A (i + 2, j) and A (i + 3, j) are also stored. It is determined whether there is a relationship of Formula 1 or 2 between them.

  When there is a relationship defined by Equation 1 or 2, the output signal OUT2 is set high, and when there is no relationship defined by Equation 1 or 2, the output signal OUT2 is set low.

  For example, the contour detector 13 includes not only the pixel value P (i, j) of the image A (i, j) but also the pixel value P (i−1, j−1) in the surrounding 3 × 3 region. , P (i, j-1), P (i + 1, j-1), P (i-1, j), P (i + 1, j), P (i-1, j + 1), P (i, j + 1) In addition, a filter circuit 13a is provided which stores nine types of pixel values in total and P (i + 1, j + 1), and applies a predetermined filtering process thereto. The type of filter is not particularly limited, and for example, a Robinson filter can be used. FIG. 5 is a schematic diagram showing a filter used in the Robinson filter. In the Robinson filter, first, the pixel value shown in FIG. 5A is multiplied for each pixel by the filter shown in FIG. 5B, and the sum is obtained. Thereafter, similarly, the pixel values shown in FIG. 5A are multiplied for each pixel by the filters shown in FIGS. 5C to 5I, and the sum of the multiplication results is obtained for each filter. Get the sum of Then, the largest value among the eight types of sums is set as the filtering result value of the pixel A (i, j) (the output value of the filter circuit 13a).

  The contour detector 13 includes an APL calculation circuit 13b that calculates an average picture level (APL) from pixel values of all pixels constituting one field based on an output value of the filter circuit 13a, and an APL calculation circuit 13b. A binarization circuit 13c is further provided for inputting a threshold value related to the output average luminance level and an output value of the filter circuit 13a. The binarization circuit 13c compares the threshold value with the output value of the filter circuit 13a, and when the output value of the filter circuit 13a is larger, the output signal OUT3 is set to low assuming that the pixel is located in the contour, When the output value of the filter circuit 13a is equal to or smaller than the threshold value, the output signal OUT3 is set high because the pixel is not located on the contour.

The moving image false contour detector 10 is provided with a flag generation circuit 16 for inputting the output signal OUT1 of the carry / carry-down discriminator 11, the output signal OUT2 of the monotonicity discriminator 12, and the output signal OUT3 of the contour detector 13. ing. When the output signals OUT1, OUT2, and OUT3 are all high with respect to the pixel value P (I, J), the flag generation circuit 16 turns on the flag F (i, j) that is the output signal. Otherwise, the flag F (i, j) is turned off. That is, the flag F (i, j) turns on the flag F (i, j) only when the following three conditions are satisfied.
(A) There is a carry / carry in the pixel values P (i, j), P (i + 1, j), P (i + 2, j) and P (i + 3, j).
(B) The pixel values P (i, j), P (i + 1, j), P (i + 2, j) and P (i + 3, j) increase or decrease monotonously.
(C) Pixels A (i, j), A (i + 1, j), A (i + 2, j) and A (i + 3, j) are not located on the contour.

  Next, the pixel value changer 20 will be described. When the moving image false contour determination flag F (i, j) for the pixel A (i, j) is on, the pixel value interchanger 20 includes a preset m rows × n columns including the pixel A (i, j). This is a circuit that replaces pixel values in the region. In the present embodiment, for example, pixel values are exchanged as shown in FIG. 6 in an area of 1 row × 4 columns. That is, when the flag F (i, j) is on, the pixel value of the pixel A (i, j) is the pixel value P (i + 2, j), and the pixel value of the pixel A (i + 1, j) is the pixel value P ( i, j), the pixel value of the pixel A (i + 2, j) is the pixel value P (i + 3, j), and the pixel value of the pixel A (i + 3, j) is the pixel value P (i + 1, j).

  Next, as the operation of the image signal processing apparatus according to the first embodiment configured as described above, a moving image false contour occurrence location specifying method and an image signal processing method will be described.

  In the present embodiment, the pixel values P (i, j) of all the pixels constituting one field are sequentially input to the moving image false contour detector 10 and the pixel value changer 20. Then, the moving image false contour detector 10 determines whether the flag F (i, j) is on or off. If the flag F (i, j) is off, the pixel value interchanger 20 outputs the input pixel value P (i, j) as it is as the pixel value P ′ (i, j), and the flag F (i, j) If j) is on, the pixel value replacer 20 replaces the input pixel value P (i, j) as shown in FIG. 6 and obtains a new pixel value P obtained as a result. '(I, j) is output.

  Here, the case where there is a carry or a carry between P (i, j) and P (i + 1, j) is a, and similarly between P (i + 1, j) and P (i + 2, j) Let b be a carry or carry, and c be a carry or carry between P (i + 2, j) and P (i + 3, j). Further, when the line of sight moves on the pixels A (i, j) to A (i + 3, j), a shift between an image recognized as vision and the original signal (hereinafter referred to as a gradation disturbance) is caused by the original signal. Is brighter (hereinafter referred to as light) or darker (hereinafter referred to as dark).

  When the line of sight moves, in one of the cases of a, b, or c in FIG. 7, as an example of the replacement method by the pixel value changer 20, it is seen after the replacement as a result of the replacement. The gradation disturbance is as shown in FIG. In FIG. 7, Δ represents gradation disturbance (carry (or down)) in a direction brighter (or darker) than the original signal, and ▲ represents a direction in darker (or brighter) direction than the original signal. Represents disturbance of gradation (carrying down (or carrying)).

  That is, in any case of a, b, or c, as shown in FIG. 7, the total number of carry is compared with the original image data input to the moving image false contour detector 10 and the pixel value interchanger 20. Alternatively, at least one of the total number of carry-downs increases, and Δ and ▲ are alternately arranged, and carry and carry are alternately arranged between a plurality of pixels that are continuous in the row direction. In any case, the absolute value of the difference between the number of carry and the number of carry is 1 or less (0 or 1).

  According to the first embodiment as described above, the moving image false contour detector 10 detects pixels assumed to generate a moving image false contour from image data for one field period. There is no need for a frame buffer that is required when detecting a pixel that is assumed to generate a moving image false contour from image data in a field. Therefore, the cost is reduced. Further, it is possible to avoid erroneous detection that occurs when detecting a moving image vector and significant deterioration of an image that occurs as a result.

  Further, as shown in FIG. 7, by changing the pixel value by the pixel value changer 20, a carry and a carry appear alternately, so that the gradation is disturbed in a direction brighter than the original signal. Disturbances in gradation in the dark direction alleviate each other, and moving image false contours are reduced.

  Next, a second embodiment of the present invention will be described. In the second embodiment, a configuration is adopted in which a motion vector is also detected when specifying the occurrence location of a moving image false contour. FIG. 8 is a block diagram showing an image signal processing apparatus according to the second embodiment of the present invention. In the second embodiment shown in FIG. 8, the same components as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the second embodiment, the delay circuit 30 that outputs the pixel value P (i, j) after being delayed by one field, and the previous one field output from the pixel value P (i, j) and the delay circuit 30. A movement / non-motion determining unit 40 is provided for detecting the movement of the pixel A (i, j) between two fields from the pixel value P (i, j). As the delay circuit 30, for example, a frame buffer can be used. The motion determination unit 40 turns off the flag F2 (i, j) when detecting motion in the pixel A (i, j), for example, and turns on the flag F2 (i, j) when no motion is detected. And Further, the flag F (i, j) output from the moving image false contour detector 10 is on between the moving image false contour detector 10 and the pixel value changer 20, and the flag output from the motion determination device 40. Only when F2 (i, j) is off, there is provided a moving image false contour detector 50 that turns on the flag F3 (i, j) that is the output signal. In the present embodiment, the pixel value changer 20 determines whether or not to change the pixel value based on the flag F3 (i, j). In the present embodiment, a motion detection circuit is configured by the delay circuit 30 and the static motion determiner 40.

  In the second embodiment configured as described above, the moving image false contour detector 10 performs the same operation as in the first embodiment, and the pixel A in the field to be detected by the moving image false contour detector 10. The static determination device 40 compares the pixel value P (i, j) of (i, j) and the pixel value P (i, j) of the pixel A (i, j) in the previous or subsequent field, Judge identity. The static determination device 40 turns on the flag F2 (i, j) when both pixel values are the same, and turns off the flag F2 (i, j) when they do not match.

  Thereafter, the moving image false contour detector 50 receives the flag F (i, j) output from the moving image false contour detector 10 and the flag F2 (i, j) output from the static motion determiner 40 as inputs, When an on flag F (i, j) is input from the contour detector 10 and an off flag F2 (i, j) is input from the static motion determiner 40, the output signal flag F3 ( i, j) are turned on and output.

  Then, the pixel value changer 20 outputs the pixel value P ′ (i, j) by the same operation as in the first embodiment.

  According to the second embodiment as described above, whether or not the image is a still image is detected by the static motion determination unit 40, and when the still image is input, the process by the pixel value interchanger 20 is not performed. Therefore, it is possible to suppress deterioration in image quality in a still image.

  Note that the image signal processing apparatus according to the first and second embodiments performs both the detection of the moving image false contour and the signal processing based on the detection result by a novel method. The present invention is not limited, and the video false contour detection may be performed by the conventional method, and then the signal processing based on the detection result may be performed by the present invention method. After execution, signal processing based on the detection result may be executed by a conventional method. In either case, the effect of the method of the present invention can be obtained. For example, Equation 1 or 2 does not necessarily hold as a condition for the pixel value to be replaced. As a result of the replacement of the pixel value, the false contour of the moving image is reduced if Δ and ▲ appear alternately.

  In addition, the detection of the contour by the moving image false contour detector 10 is performed to prevent the contour from blurring, and is not necessarily required to reduce the moving image false contour. Further, when performing contour detection, it is preferable to turn off the flag not only for pixels in which the contour actually exists in the input image data, but also for the surrounding pixels. This is because even if the flag is turned off only for a pixel that actually has a contour, if the pixel value is replaced by the pixel value interchanger 20 for the surrounding pixels, the contour may be blurred. The aforementioned Robinson filter is suitable for such processing because it outputs a comparatively gentle peak. For example, when a filter is applied to 3 × 3 pixels, it is assumed that a contour exists in the range of about 8 × 8 or 16 × 16 pixels, and the output signal OUT3 for these pixels is set to low. To do.

  Furthermore, the replacement of the pixel values is not limited to that shown in FIG. 6. For example, as shown in FIG. 9A, the pixel values may be replaced between two pixels. As shown in FIG. 9B, the pixel values may be interchanged for every two pixels. In FIG. 9, Δ indicates a position where a carry is present, and ▲ indicates a position where a carry is present.

  Furthermore, the number of subfields and the number of gradations constituting one field period are not particularly limited. For example, as shown in FIG. 10, 32 gradations may be expressed by seven subfields arranged in the order of 1: 2: 3: 4: 5: 7: 9. Further, as shown in FIG. 11, the subfield with the highest weight is placed at the center of one field period, and two subfields with the same weight are arranged before and after the subfield to express 64 gradations. Good. Even in this case, the presence / absence of carry or carry is determined based only on the weight of the subfield that emits light, and is not affected by the arrangement position of the subfield.

  Further, the replacement of pixel values is not limited to the pixels arranged in the row direction, and the same effect can be obtained even when the pixel values are replaced in the column direction. The number of pixels to be replaced may be an arbitrary continuous area of m rows × n columns. In this case, as shown in FIG. 12, the pixel values are changed so that the gradation disturbance appears alternately. Replace.

  Further, the display device capable of the present invention is not limited to the plasma display, but can be applied to a device employing the subfield method, such as a mirror device and an organic EL display.

1 is a block diagram illustrating an image signal processing apparatus according to a first embodiment of the present invention. It is a figure which shows the content of the lookup table LUT. It is a figure which shows the content of the table for carry / decay. 2 is a block diagram showing a configuration of a moving image false contour detector 10. FIG. It is a schematic diagram which shows the filter used with a Robinson filter. It is a figure which shows how to change the pixel value by the pixel value changer 20. It is a figure which shows the mode of dispersion | distribution of the moving image false contour in 1st Embodiment. It is a block diagram which shows the processing apparatus of the image signal which concerns on the 2nd Embodiment of this invention. It is a figure which shows the example of how to replace a pixel value. It is a figure which shows the example of the light emission / non-light-emission state at the time of comprising 1 field period by 7 subfields. It is a figure which shows the example of the light emission / non-light-emission state at the time of providing two or more subfields with equal weight within 1 field period. It is a schematic diagram which shows the disorder of the gradation in the pixel arrange | positioned by the area | region arrangement | sequence of m row xn column.

Explanation of symbols

10; moving image false contour detector 11; carry / carry discriminator 12; monotonic discriminator 13; contour detector 16; flag generator circuit 20; pixel value changer 30; delay circuit 40; Video false contour detector

Claims (13)

In a method of processing an image signal, one field period is divided into a plurality of subfields having different luminance relative ratios, and an image signal is processed to cause a display device to express gradation by combining the luminance for each subfield. And changing the gradation level arrangement by exchanging the pixel values of specific pixels among the four pixels arranged in the display device in succession and having the pixel values monotonously increasing or decreasing , A method for processing an image signal, comprising the step of increasing at least one of a total number of carry-ups and a total number of carry-downs of subfields included in a key level array. 2. The image signal according to claim 1, wherein an absolute value of a difference between a total number of carry and a total number of carry-down after the change of the arrangement becomes 0 or 1 by increasing at least one of the image signals. Processing method. 3. The method of processing an image signal according to claim 1, wherein a carry and a carry appear alternately within a gradation level of the plurality of pixels by increasing at least one of the plurality of pixels. 4. The image signal processing method according to claim 1, wherein the step of increasing at least one includes a step of switching each gradation level between two pixels. 5. 5. The image signal processing method according to claim 4, wherein the two pixels are adjacent to each other. In an image signal processing apparatus that divides one field period into a plurality of subfields having different luminance relative ratios and processes an image signal for causing a display apparatus to express a gradation by a combination of the luminances of the subfields. And changing the gradation level arrangement by exchanging the pixel values of specific pixels among the four pixels arranged in the display device in succession and having the pixel values monotonously increasing or decreasing , An apparatus for processing an image signal, comprising: a pixel value changer that increases at least one of a total number of carry-ups and a total number of carry-downs of subfields included in a key level array. In addition, the gradation level in the one field period smoothly changes between the four pixels arranged in succession on the display device, and the plurality of pixels in the one field period. A detector for detecting a pixel including a carry or a carry of at least one subfield in an array of gradation levels, wherein the pixel detected by the detector is converted to a gradation level by the pixel value interchanger; The image signal processing device according to claim 6, wherein the image signal is included in the four pixels whose arrangement is changed. In addition, the gradation level within the one field period smoothly changes between the four pixels arranged in succession on the display device, and includes two adjacent pixels included in the plurality of pixels. A detector for detecting a pixel whose amount of change in the light emission time zone within the one field period is equal to or greater than a predetermined value between the pixels, and the pixel detected by the detector is converted by the pixel value changer. 7. The image signal processing apparatus according to claim 6, wherein the arrangement of tone levels is included in the four pixels to be changed. The pixel value interchanger sets the absolute value of the difference between the total number of carry and the total number of carry after the array change to 0 or 1, according to any one of claims 6 to 8. The image signal processing apparatus described. The image signal processing according to any one of claims 6 to 9, wherein the pixel value interchanger alternately causes a carry and a carry within a gradation level of the plurality of pixels. apparatus. 11. The image signal processing apparatus according to claim 6, wherein the pixel value interchanger interchanges each gradation level between two pixels. 11. 12. The image signal processing apparatus according to claim 11, wherein the two pixels are adjacent to each other. A motion detection circuit that detects the motion of an image by comparing the image signal of the one field period and the image signal of the one field period immediately before or immediately after the image signal, and based on both output signals of the detector and the motion detection circuit The image signal processing apparatus according to claim 7 , further comprising: a second detector that determines whether or not the array is changed by a pixel value interchanger.

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