JP2016142783A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device in an inexpensive configuration, with which it is possible to adapt pseudo-grayscale generation means for pixels that require a minute grayscale expression such as gradation, and to compress bit depth so as to avoid the adaption of the pseudo-grayscale generation means for other pixels.SOLUTION: The display device comprises: bit conversion means for converting inputted m bits of pixel to n bits (<m); pseudo-grayscale generation means for generating pseudo-grayscale from the information of m-n bits reduced by the bit conversion means; histogram means for counting the number of occurrences of each gray level, for all pixels in a one-frame period; and pseudo-grayscale control means for exerting determination and control so as to acquire from the histogram means, for each of inputted pixel values, the number of occurrences of a near gray level to the pixel value of a preceding frame (including an equal gray level), and, when there exist a plurality of gray levels in which the number of occurrences exceeds a threshold, to add the output of the pseudo-grayscale generation means to the output value of the bit conversion means, or otherwise, to output directly.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a display device that displays an input video signal, and more particularly, to a projection display device such as a liquid crystal projector device or a DLP (Digital Light Processing) projector device, or a liquid crystal display.

  A display device such as a liquid crystal projector or a liquid crystal display has a deep bit depth when image processing is performed internally, but may perform a process of converting the bit depth to a shallower one when outputting to a liquid crystal panel or the like. . In that case, as a technique for artificially holding lost gradation information, pseudo gradation generation means such as a dither method for distributing an error amount to neighboring pixels and an FRC (frame rate control) method for distributing to an adjacent frame are known. ing.

  However, by applying the pseudo gradation generation means, there may be an adverse effect. For example, when coordinate conversion processing such as resolution conversion is performed after applying a dither method to a raster image, a pattern that was not present in the original image may occur due to filter processing during coordinate conversion.

  In addition, when the FRC method is applied at a gradation in which the luminance gradation characteristic of the liquid crystal panel is not smooth, the luminance difference for each frame may increase and be visually recognized as flicker.

  With respect to this problem, in Patent Document 1, the minimum value of the difference between the input gradation value of each pixel and the gradation value of its surrounding pixels is less than or equal to the threshold value, and the gradation value of the pixel is less than or equal to the threshold value. The technique which applies a dither system when it is, and an FRC system when it is not so is disclosed. By doing in this way, the brightness | luminance difference between frames at the time of applying a FRC system becomes small, and it is avoided that a flicker is visually recognized.

  Also, for gradations to which the FRC method cannot be applied, the dither method is applied when the difference in gradation from surrounding pixels is small, so that a gradation image can be displayed smoothly. Since the dither method and the FRC method are not applied to the portions other than the gradation, the fidelity to the input video is inferior. However, since there is no gradation to be compared in the first place, the user can use it without a sense of incongruity.

JP 2010-176082 A

  The above-described prior art makes the surrounding pixels wider than four sides, but each has the following problems. First, in the four-way case, the pseudo gradation generation means is applied only to the transition of the gradation with respect to the gentle gradation image, resulting in a difference in level from that which should originally have the same gradation value. Next, in the case where the width is larger than that, it is necessary to have a sufficient buffer in the vertical direction and widen the comparison pixels in order to produce an effect on the gradation image in the vertical direction. In addition, since it is necessary to perform the calculation at high speed, there is a problem that the cost is high.

  Therefore, an object of the present invention is to apply pseudo gradation generation means to pixels that require fine gradation expression such as gradation, and to avoid application of pseudo gradation generation means to pixels that do not. Another object of the present invention is to provide a display device capable of compressing the bit depth with an inexpensive configuration.

  In order to achieve the above object, a display device according to the present invention includes bit conversion means for converting an input m-bit pixel into n (<m) bits, and mn bits reduced by the bit conversion means. Pseudo gradation generation means for generating pseudo gradation from the information of the above, histogram means for counting the number of appearances of each gradation for all pixels in one frame period, and for each input pixel value from the histogram means The number of appearances of neighboring gradations (including equal gradations) of the pixel value of the previous frame is acquired, and when there are a plurality of gradations where the number of appearances exceeds the threshold, the output value of the bit conversion means is A pseudo gray scale that adds and outputs the pseudo gray scale generation means, and determines and controls to output the output value of the bit conversion means as it is when there are no multiple gray scales whose appearance count exceeds the threshold value. Control hand , Characterized in that it comprises a door.

  According to the present invention, the pseudo gradation generation means is applied to pixels that require fine gradation expression such as gradation, and the bit is applied so as to avoid application of the pseudo gradation generation means to pixels that do not. A display device capable of compressing the depth can be provided with an inexpensive configuration.

The block block diagram of the display apparatus in the 1st Embodiment of this invention Example of control flow of determination unit 8 in the first embodiment of the present invention Example of the result of counting the number of appearances of partial gradations in a frame by the histogram unit 2 according to the first embodiment of the present invention An example of a dither table in the pseudo gradation generation unit 4 in the first embodiment of the present invention The block block diagram of the display apparatus in the 2nd Embodiment of this invention. The figure which showed the positional relationship of the comparison pixel in the pseudo | simulation gradation availability determination part 12 in the 2nd Embodiment of this invention. Example of Operation of Pseudo-Grayscale Acceptability Determination Unit 12 and Determination Result Table 13 in the Second Embodiment of the Present Invention

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is applicable to display devices such as a liquid crystal projector device, a DLP (Digital Light Processing) projector, and a liquid crystal display device.

[Example 1]
A display device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a display device according to the first embodiment of the present invention. The display device includes an image processing unit 1, a histogram unit 2, a bit depth conversion unit 3, a pseudo gradation generation unit 4, a pseudo gradation control unit 5, an addition unit 6, and a display unit 7.

  The image processing unit 1 performs image processing such as gamma on an input video having an 8-bit depth, and outputs the video at a 10-bit depth.

  The histogram section 2 (histogram means) counts the number of appearing pixels of all gradation values of 10-bit data for all pixels of the frame. An example of the result of counting the number of appearances of some gradations in a certain frame is shown in FIG.

  The bit depth conversion unit 3 (bit conversion means) outputs the upper 8 bits of the input 10-bit pixel data to the addition unit 6 and the lower 2 bits to the pseudo gradation generation unit 4.

  The pseudo gradation generation unit 4 (pseudo gradation generation means) performs pseudo gradation generation by a dither method. The 2-bit gradation data of the pixel and the least significant bit (LSB) data of the horizontal and vertical coordinates are input, and 1-bit gradation data is output according to the dither table of FIG. By doing this, horizontal and vertical 2 × 2 pixels are used as one unit, and a gray scale exceeding the bit depth can be expressed in a pseudo manner by the average value. For example, the gradation value 2 is 1/2 in the 8-bit depth range, and since 2 out of 4 pixels are 1, it is expressed as 1/2 by the integration effect. Although the dither method is used in the present embodiment, there is no change in the FRC method or other error diffusion methods.

  The pseudo gradation control unit 5 (pseudo gradation control means) includes a determination unit 8 and a selector 9, and uses the gradation data of the input pixel and the result of the histogram unit 2, and the pseudo gradation generation unit 4 outputs 1-bit gradation data or 0. The determination unit 8 controls the selector 9 according to a control flow described later. The selector 9 has two 1-bit input ports, and is connected to the output of the pseudo gradation generation unit 4 and the fixed 0 output, and outputs the input of any port as it is under the control of the determination unit 8.

  The addition unit 6 adds the 8-bit data from the bit depth conversion unit 3 and the 1-bit data from the selector 9 and outputs the result to the display unit 7 as 8-bit data. When the data from the bit depth conversion unit 3 is 255, 255 is output regardless of the output of the selector 9. The display unit 7 converts the input 8-bit video data into an optical video and outputs it to a screen (not shown).

  A control flow of the determination unit 8 will be described with reference to FIG. FIG. 2 is a flow up to the setting of the selector 9 for each pixel, which is performed in the determination unit 8.

  In step S201, the gradation data of the target pixel is substituted for the variable Lx. In step S202, the number of appearances of each gradation in the previous frame in the range from −4 to +4 of the variable Lx is acquired from the histogram unit 2 and substituted into the variables F [0] to F [8]. Here, the peripheral gradation range to be referred to is matched with the gradation range lost in the bit conversion unit 3 as a preferable example, but may be expanded or narrowed as appropriate according to the configuration of the display device.

  In step S203, it is determined whether or not there are two or more variables larger than the threshold value among the variables F [0] to F [8]. If there are any, branch to step S204, and if not, branch to S205. . In step S204, the selector 9 is set to the output side of the pseudo gradation generation unit 4. On the other hand, step S205 sets the selector 9 to the 0 output fixed side.

  As for the threshold value in step S203, it is desirable to set the threshold value as low as near 0 when there is no coordinate conversion processing such as resolution conversion in the subsequent stage of the adding unit 9 as in the display device of the present embodiment. On the other hand, if the configuration of the display device is provided with a coordinate conversion processing unit at the subsequent stage of the adding unit 9, the case of creating a pattern in which the pseudo gradation does not originally exist becomes high. It is desirable to set and make it difficult to output the pseudo gradation. When the threshold value is set to 0 and the result of the number of appearances shown in FIG. 3 is obtained, since the number of appearances is greater than 0 in the gradation values 123 and 126 with respect to the gradation values 122 to 127, the selector 9 generates the pseudo gradation generation unit. Set to 4 side.

  On the other hand, since the lower 2 bits are 2 in decimal notation, the gradation value 510 is a gradation level that cannot be expressed without using the pseudo gradation, but the number of appearances of 506 to 514 excluding the gradation value 510 is Since all are 0, the selector 9 is set to 0 output side.

  As described above, the display device according to the present embodiment uses the histogram unit 2 to determine whether there is a pixel with a gradation level (not equal to) that is close to the gradation level of the target pixel in the same frame. Judgment is made. As a result, the output of the pseudo gradation generation unit 4 is applied to pixels that require fine gradation expression such as gradation, and the application of pseudo gradation generation means is avoided for pixels that do not. Bit depth compression is possible. Moreover, since application to all pixels in one frame can be realized in a one-dimensional memory called a histogram, it is inexpensive.

  In the present embodiment, the peripheral gradation range referred to by the determination unit 8 in S202 is specified as -4 to +4. However, the data output from the bit depth conversion unit 3 to the addition unit 6 is the minimum range. It is sufficient that the upper 8 bits are larger than the matching range. Further, the count value of the histogram portion 2 is the result of one frame before, but since most of the application of pseudo gradation is for a still image, a sufficient effect can be obtained. However, it is preferable to further include a moving image determination unit that determines whether or not the input video is a moving image, and when it is determined that the input image is a moving image, the selector unit 9 always sets the output on the pseudo gradation generation unit 4 side. This is a more preferable form.

[Example 2]
A display apparatus according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a block diagram of a display device according to the second embodiment of the present invention. The display device includes an image processing unit 1, a one-line delay unit 10, a one-pixel delay unit 11, a pseudo gradation determination unit 12, a determination result table 13, a bit depth conversion unit 3, a pseudo gradation generation unit 4, and a pseudo gradation unit. A control unit 14, an addition unit 6, and a display unit 7 are included.

  Since the image processing unit 1, the bit depth conversion unit 3, the pseudo gradation generation unit 4, the addition unit 6, and the display unit 7 are the same as those in the first embodiment, description thereof is omitted. A one-line delay unit 10 (one-line delay unit) delays the input grayscale data of one pixel by one line and outputs it. A one-pixel delay unit 11 (one-pixel delay means) delays the input pixel gradation data by one pixel and outputs it. The pseudo gradation determination unit 12 (pseudo gradation determination unit) calculates difference values between the input pixel gradation data and the gradation data output from the one-line delay unit 10 and the one-pixel delay unit 11, respectively. An arithmetic operation is performed to determine whether or not the pseudo gradation is a good gradation. The determination method will be described later.

  The determination result table 13 (determination availability table) is a table for holding pseudo gradation rejection determination results for all gradations. The initial value is NO for all gradations, and is updated by the output of the determination result of the pseudo gradation determination unit 12. It is initialized every time the frame is switched, and the determination result of the previous frame is output in response to the reference request for the determination result of each gradation.

  The pseudo gradation control unit 14 (pseudo gradation control means) includes a selector control unit 15 and a selector 9, and when the output value of the determination result table for the input pixel gradation data is acceptable, the selector 9. Is controlled to the output side of the pseudo gradation generation unit 4, and if not, it is controlled to the 0 output side. Here, the selector 9 is the same as that of the first embodiment.

  A determination method in the pseudo gradation determination unit 12 will be described with reference to FIGS. 6 and 7 using actual examples. FIG. 6 is a diagram showing the positional relationship of the comparison pixels in this embodiment. As shown in FIG. 6, the output pixel 62 of the one-line delay device 10 is a pixel above the target pixel 61, and the output pixel 63 of the one-pixel delay device 11 is a pixel on the left of the target pixel 61. Therefore, the determination is made based on the calculation result of the upper pixel and the left pixel. Here, the reason why the calculation is not performed with the right pixel or the lower pixel is that the target pixel will eventually move to the right or the lower, and will eventually be calculated.

  When the difference value is within the range of -4 to +4 as a result of calculation with the upper and left pixels, the gradation belonging to the range -4 to +4 with respect to each gradation is determined to be pseudo gradation, and the determination is made. Output to the result table 13. For example, when the gradation data of the target pixel, the upper pixel, and the left pixel are 516, 511, and 518, respectively, as shown in FIG. The description will be given with reference. FIG. 7 shows an update operation of the drafting result table 13 according to the pseudo gradation availability determination result performed by the pseudo gradation availability determination unit 12 when the gradation data of FIG. 6 is input. is there.

  First, attention is focused on the gradation data between the target pixel and the upper pixel. Since the difference of the gradation data is outside the range of 5 and −4 to +4, the determination result is negative and the determination result table 13 is not updated. Next, attention is focused on the target pixel and the left pixel. Since the difference between the gradation data is in the range of 2 and −4 to +4, the determination result is acceptable, and the determination result table 13 is updated. The gradation to be updated is a gradation corresponding to the range of -4 to +4 from the gradation data of the target pixel and the left pixel, respectively, and as shown in FIG. Is updated. The determination result is referred to by the pseudo gradation control unit 14 in the next frame as described above.

  As described above, the display device according to the present embodiment uses the one-line delay unit 10, the one-pixel delay unit 11, and the pseudo gradation determination unit 12 to determine whether the gradation level difference between adjacent pixels is small. The determination is made and the result is stored in the determination availability result table 13. As a result, it is possible to obtain an effect not in the first embodiment in which the pseudo gradation is applied only when there is a gradation portion. Further, as in the first embodiment, the application to all the pixels of the frame can be realized in a one-dimensional memory called the determination result table 13, so that it is inexpensive. Further, in the present embodiment, the range for determining that the gradation level is close in the pseudo gradation determination unit 12 is specified as −4 to +4. However, the minimum range is the bit depth conversion unit 3 to the addition unit 6. It is sufficient that the upper 8 bits, which are the data output to, are wider than the matching range.

  Further, the determination result table 13 outputs the determination result of one frame before. However, as in the first embodiment, since much of the application of the pseudo gradation is for a still image, a sufficient effect is obtained. can get. However, it is preferable to further include a moving image determination unit that determines whether or not the input video is a moving image, and when it is determined that the input image is a moving image, the selector unit 9 always sets the output on the pseudo gradation generation unit 4 side. This is a more preferable form.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

1 image processing section, 2 histogram section (histogram means),
3 bit depth conversion section (bit conversion means), 4 pseudo gradation generation section (pseudo gradation generation means),
5 pseudo gradation control section (pseudo gradation control means), 6 addition section, 7 display section, 8 determination section,
9 Selector

Claims (5)

Bit conversion means for converting an input m-bit pixel into n (<m) bits;
Pseudo gradation generation means for generating pseudo gradation from information of mn bits reduced by the bit conversion means;
Histogram means for counting the number of appearances of each gradation for all pixels in one frame period;
For each input pixel value, the number of appearances of neighboring gradations (including equal gradations) of the pixel value of the previous frame is acquired from the histogram means, and a plurality of gradations with the number of appearances exceeding the threshold value are obtained. If present, the output of the pseudo gradation generating means is added to the output value of the bit converting means, and if there are not a plurality of gradations whose appearance count exceeds the threshold value, the output value of the bit converting means And a pseudo gradation control means for determining and controlling to output the image as it is. The display device according to claim 1, wherein the neighborhood gradation indicates a gradation in which the n bits are equal. Bit conversion means for converting an input m-bit video into n (<m) bits;
Pseudo gradation generation means for generating pseudo gradation from information of mn bits reduced by the bit conversion means;
1-line delay means for delaying and outputting the pixel value of the input video by 1 line period;
1-pixel delay means for outputting a pixel value of the input video with a delay of 1 pixel period;
a determination result table for holding a pseudo gradation determination result of each m-bit gradation for one frame period;
For each pixel value of the input video, when the pixel value is compared with the outputs of the one-line delay means and the one-pixel delay means, the comparison result is different and the difference value is within a predetermined range. A pseudo gradation determination unit that sets pseudo gradation determination results for all gradations within the range of the determination result table;
For each pixel of the input video, according to the pseudo gradation determination result of the determination result table of the gradation of the pixel, if possible, the output of the pseudo gradation generation means is output to the output value of the bit conversion means. And a pseudo gradation control means for controlling to output the output value of the bit conversion means as it is when the result is negative. The display device according to claim 3, wherein the range is a gray scale in which the n bits are equal. The display device according to any one of claims 1 to 4, further comprising a motion detection unit that determines whether or not the input video has moved with respect to the input video of one frame before.
The display device characterized in that the pseudo gradation control means performs control so as to always add the output of the pseudo gradation generation means when the determination result of the motion detection means is motion.