JP4741882B2 - Image reproduction apparatus, liquid crystal display, liquid crystal projector, and image reproduction method - Google Patents

Description

  The present invention relates to an image reproduction device that reproduces an image displayed on a liquid crystal panel, a liquid crystal display, a liquid crystal projector, and an image reproduction method.

  In general, an apparatus for displaying an image on a liquid crystal panel has a driving voltage-transmittance characteristic peculiar to the liquid crystal panel. This drive voltage-transmittance characteristic is a characteristic in which the relationship between the drive voltage for driving the liquid crystal panel and the transmittance for displaying an image on the screen of the liquid crystal panel is not linear. Because of this characteristic, if the digital image signal input to this device is directly converted from digital to analog and input to the liquid crystal panel, the relationship between the input digital image signal and the transmittance of the liquid crystal panel becomes nonlinear. In particular, the amount of change in transmittance per gradation becomes small with respect to the amount of change in the input digital image signal on the low gradation side and the high gradation side, and the image displayed on the liquid crystal panel is significantly deteriorated. .

  In order to prevent this deterioration, an LUT (Look Up Table) that is a comparison table of the input signal and the output signal is provided in the front stage of the mechanism that performs digital-analog conversion on the input signal, and the input signal is received by the provided LUT. By the conversion, the digitized luminance gradation data is corrected to an arbitrary gradation with respect to the drive voltage-transmittance characteristic.

  FIG. 12 is a diagram showing drive voltage-transmittance characteristics specific to a liquid crystal panel.

  As shown in FIG. 12, since the relationship between the driving voltage and the transmittance in the liquid crystal panel is non-linear, the digital image signal input to the image reproduction apparatus having the liquid crystal panel is input as it is as the driving voltage of the liquid crystal panel. The above-mentioned problem will occur.

  FIG. 13 is a diagram illustrating a relationship between the input image signal and the transmittance when the input image signal is converted using the LUT.

  As shown in FIG. 13, the input image signal is converted in the LUT, and the converted signal is input as drive power to the liquid crystal panel, so that the relationship between the input image signal and the transmittance of the liquid crystal panel becomes linear.

  FIG. 14 is a diagram illustrating a relationship between an input signal and an output signal in the LUT.

  The input image signal input to the liquid crystal panel having the drive voltage and transmittance characteristics shown in FIG. 12 is converted using the LUT that converts the input signal shown in FIG. 14 into an output signal. As shown in FIG. 13, the relationship between the input image signal and the transmittance of the liquid crystal panel is linear. The LUT shown in FIG. 14 converts an 8-bit input signal into a 10-bit output signal.

  In recent years, the maximum peak level of an input signal is detected, the amplification factor of the input signal is calculated from the detected maximum peak level, the input signal is amplified by the calculated amplification factor, and the amplified signal is based on the amplified signal. A method of reproducing an image on a liquid crystal panel has been considered (for example, see Patent Document 1).

Further, there is a method of approximating the drive voltage-transmittance characteristics using a plurality of straight lines or curves, and converting the gradation of the input signal according to the gamma correction data using the approximate characteristics to reproduce the image on the liquid crystal panel. It is considered (for example, refer to Patent Document 2).
JP 2003-099010 A JP-A-11-296149

  However, in the conventional digital signal conversion processing using the LUT, an 8-bit-8-bit or 8-bit-10-bit LUT is often used, but the number of bits of the output signal of these LUTs is more accurate in the output signal. The unit that can be set for expressing the tone is rough, and the input image signal and the transmittance of the liquid crystal panel are not always perfectly linear as shown in FIG. 13 due to the conversion in the LUT, and the desired color may not be reproduced. In some cases, gradation skipping or the like occurs, and in particular, low gradation or halftone gradation reproducibility is not good on the LUT. In order to avoid this, in order to make the output signal value as fine as possible, it is possible to increase the memory capacity of the LUT and increase the number of bits in the comparison table. However, this leads to an increase in the cost of this apparatus. There is a problem.

  Further, in the method described in Patent Document 1, contrast is visually emphasized by always enhancing an image in a low gradation portion and a high gradation portion corresponding to the maximum peak level. The improvement of image reproducibility is not considered.

  In the method described in Patent Document 2, by using approximate characteristics, the memory capacity is reduced, and the number of accesses to the memory is only reduced to perform high-speed processing. The improvement of reproducibility is not considered.

  The present invention has been made in view of the problems of the prior art as described above, and is an image reproduction apparatus capable of enhancing gradation in all gradations without increasing the cost of the apparatus. An object of the present invention is to provide a liquid crystal display, a liquid crystal projector, and an image reproduction method.

In order to achieve the above object, the present invention provides:
An image reproduction device for displaying an image on a liquid crystal panel based on an image signal,
A contrast table for associating a drive signal for displaying an image on the liquid crystal panel with the image signal;
Digital-analog conversion means for converting the image signal output from the comparison table into an analog video signal and outputting the analog video signal;
Amplifying means for multiplying the video signal output from the digital-analog converting means by an amplification factor;
Input detection means for detecting a maximum value or a minimum value within a predetermined time of the image signal;
Based on the maximum value or minimum value of the image signal detected by the input signal detection means, the stored contents of the contrast table are rewritten , and the drive voltage output to the liquid crystal panel rewrites the stored contents of the contrast table. and a control means to change the amplification factor of said amplifying means so as to be substantially the same voltage as after previous rewriting.

  Further, the control means is configured so that the output range of the image signal uses all areas of the comparison table based on the maximum value or the minimum value of the image signal detected by the input signal detection means. The stored contents of the table are rewritten.

Further, the said control table and said Rukoto is stored smoothing process has been applied value.

An image reproduction method using a contrast table that stores a drive signal for displaying an image on the liquid crystal panel in an image reproduction device that displays an image on the liquid crystal panel based on the image signal in association with the image signal,
A process of converting an image signal output from the comparison table into an analog video signal;
A process of multiplying the converted analog video signal by an amplification factor;
A process for detecting a maximum value or a minimum value in a predetermined time of the image signal;
Processing to rewrite the stored contents of the comparison table based on the detected maximum value or minimum value of the image signal ;
And a process of changing the amplification factor so that the drive voltage output to the liquid crystal panel becomes substantially the same voltage before and after rewriting the stored contents of the comparison table .

  Further, the stored contents of the comparison table are rewritten based on the detected maximum value or minimum value so that the output range of the image signal uses all areas of the comparison table.

  In the present invention configured as described above, a maximum value or a minimum value within a predetermined time is detected for an input image signal, and a drive signal for displaying an image on the liquid crystal panel is stored in association with the image signal. The stored contents of the comparison table are rewritten based on the detected maximum value or minimum value.

  For this reason, by effectively using the memory, the memory capacity, which is an actual reference table, is not increased, and it is not limited to colors of low gradations or high gradations. Since the gradation can be corrected to a fine gradation, the gradation can be improved.

  As described above, in the present invention, the maximum or minimum value within a predetermined time is detected for the input image signal, and the drive signal for displaying the image on the liquid crystal panel is stored in association with the image signal. Since the stored contents of the table are rewritten based on the detected maximum value or minimum value, the gradation can be improved in all gradations without increasing the cost of the apparatus.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing an embodiment of an image reproduction apparatus of the present invention.

  As shown in FIG. 1, an image reproduction device 100 according to this embodiment corrects an image signal detected by the input signal detection unit 1 and an input signal detection unit 1 that detects an image signal input to the image reproduction device 100. LUT2, which is a comparison table, digital-analog converter 3 that performs digital-analog conversion on the image signal corrected by LUT2, and amplification that amplifies the image signal digital-analog converted by digital-analog converter 3 Unit 4, liquid crystal panel 5 that displays an image based on the image signal amplified by amplification unit 4, and control that controls LUT 2 and amplification unit 4 based on the image signal detected by input signal detection unit 1 Part 6. The LUT 2 in this embodiment uses an 8-bit-10-bit comparison table configuration.

  Hereinafter, an image reproduction method in the image reproduction apparatus 100 shown in FIG. 1 will be described.

  FIG. 2 is a sequence diagram for explaining an image reproduction method in the image reproduction apparatus 100 shown in FIG.

  First, when an image signal is input to the input signal detection unit 1 of the image reproduction apparatus 100 shown in FIG. 1 (step S1), the input image signal is detected within a detection range set in advance by the input signal detection unit 1. The maximum value is detected (step S2). The detection range here represents a certain cycle, and may be one frame of an input image signal or may be a preset number of frames. Further, a timer is provided in the input signal detection unit 1, a timeout value is set in advance in the provided timer, and the maximum value is detected in the time unit with the time when the timer expires as a predetermined time. Also good.

  The input image signal is output from the input signal detection unit 1 and input to the LUT 2 (step S3).

  When the maximum value detected by the input signal detection unit 1 is output to the control unit 6, the maximum value output from the input signal detection unit 1 is input to the control unit 6 (step S4), and the input maximum value Based on the above, the use area of the LUT 2 is determined by the control unit 6 (step S5).

  FIG. 3 shows the relationship between an input signal whose maximum value detected in a preset detection range is 128 and an output signal corrected by the LUT 2 that is not controlled by the control unit 6 for the input signal. FIG. Note that the output signal shown in FIG. 3 is a 10-bit digital signal that is output after the input signal input to the LUT 2 is corrected without being controlled by the control unit 6.

  As shown in FIG. 3, the maximum value of the input signal detected by the input signal detector 1 is 128, and the value of the output signal at that time is 512. Since the maximum value that can be output as an output signal in the LUT2 that expresses the output signal in 10 bits is 1024, it is determined that the value of the output signal that is not used in this detection range can also be used in the area from 513 to 1024, The LUT2 area corresponding to the output signal value of 1024 is determined as the use area in the LUT2.

  Next, correction of the output signal in the above-described use area is performed. The maximum value of the current output signal shown in FIG. 3 is 512, and the ratio with respect to 1024 which is the maximum value of the used area determined in step S5 is 50%. Therefore, when the correction by the LUT 2 is performed, the control unit 6 performs control to set the ratio of the output signal to the use area to 100%.

  FIG. 4 shows the relationship between an input signal whose maximum value detected in a preset detection range is 128 and an output signal corrected by the LUT 2 controlled by the control unit 6 for the input signal. FIG. The output signal shown in FIG. 4 is a 10-bit digital signal that is output after the input signal input to the LUT 2 is corrected and controlled by the control unit 6.

  As shown in FIG. 4, the image signal input to the LUT 2 is (the output signal corresponding to the input signal shown in FIG. 3 × (used area / input signal detection unit 1 determined in step S5 is detected). The value of the output signal shown in FIG. 3 with respect to the maximum value of the input signal is corrected by the LUT 2 (step S6), resulting in the output signal shown in FIG. That is, a value obtained by doubling the output value corrected using the LUT 2 that is not controlled by the control unit 6 becomes the value of the output signal corrected using the LUT 2 controlled by the control unit 6.

  5 is an enlarged view of a portion A shown in FIG. 3, and FIG. 6 is a diagram showing a state where the value of the output signal shown in FIG. 5 is doubled. In the drawing, each dot of the digital signal corresponding to the signal is indicated by hatching. As shown in FIG. 6, it cannot be said that the gradation is converted into a fine gradation only by doubling the value of the output signal shown in FIG. In view of this, the control unit 6 performs control to output a drive signal that has been smoothed in consideration of the correlation with the values before and after the output signal as described below.

  When the value of the output signal is the same value for a plurality of input signals, the number of input signals that have the same value of the output signal, the value of the output signal, and the value of the output signal that changes next Output signal is controlled to a suitable value.

  In the case of the example shown in FIG. 6, the value of the output signal for the input signals 61 to 64 is 806, and the value that changes next is 808 for the input signal 65. Here, since the value of the output signal for the input signal 64 is 806, the value of the output signal for the next input signal 65 is 808, and the difference is 2, the value of the output signal for the input signal 64 is from 806. It is controlled to 807. Similarly, the value of the output signal with respect to the input signal 69 is controlled from 808 to 809.

  FIG. 7 shows a state of control for an output signal when the value of the output signal is not the same between the input signals before and after, and the value of the next output signal is the same among a plurality of consecutive input signals. FIG.

  As shown in FIG. 7, when the value 806 of the output signal with respect to the input signal 65 is different from the value of the output signal with respect to the preceding and succeeding input signals, the input signals with the next output signal value of 808 are 66-69. In the case where the values are consecutive, the control may be performed so that the output signal value 808 corresponding to the input signal 66, which is the first value of the next output signal, is decreased by one to 807.

  FIG. 8 is a diagram illustrating how the output signal is controlled when the difference from the value of the output signal that changes next is four.

  As shown in FIG. 8, when the value of the output signal for the input signal 65 that changes next to the value 804 of the output signal for the input signals 61 to 64 is 808, the difference between the two output signals is 4. The output signal value for the signal 64 may be controlled from 804 to 807, the output signal value for the input signal 63 may be controlled from 804 to 806, and the output signal value for the input signal 62 may be controlled from 804 to 805. .

  FIG. 9 is an enlarged view of a portion C shown in FIG. 4 and is controlled by the control unit 6 described in FIG.

  Comparing FIG. 5 and FIG. 9, in FIG. 9, the output signal corrected for the input signal in the halftone is continuously finely changed as a digital signal in FIG. As a result, it is understood that the possibility of gradation skip is reduced and the reproducibility of gradation is improved.

  10 is an enlarged view of a portion B shown in FIG. 3, and FIG. 11 is an enlarged view of a portion D shown in FIG. In each figure, each dot of the digital signal corresponding to the signal is indicated by hatching.

  FIG. 11 shows a case where the output signal of FIG. 10 is doubled, and thus no improvement in gradation is observed. However, the maximum value of the input signal detected by the input signal detector 1 and its value are not shown. Depending on the output signal at the time, when the used area is 1.2 times or 2.3 times, the decimal point is rounded to make the output signal value 1.2 times or 2.3 times an integer value. There is a need. At this time, an integer value obtained by rounding off the decimal point is obtained by the control unit 6 based on the correlation with the preceding and succeeding values so that a smoothed drive signal that does not cause gradation skipping is output.

  For example, if the difference between the value of the previous output signal and the value of the subsequent output signal is equal, or if the rate of change of the output signal has decreased, the previous output An integer value is obtained such that the difference from the value of the subsequent output signal is smaller than the difference from the value of the signal. In this way, it can be corrected to a more suitable gradation, and it can be seen that the reproducibility of gradation is improved.

  When the corrected image signal is output from the LUT 2 as a drive signal for driving the liquid crystal panel 5 (step S7), the image signal output from the LUT 2 is input to the digital-analog converter 3, and the analog signal is converted from the digital signal. (Step S8), and the image signal converted into an analog signal is output from the digital-analog converter 3 to the amplifier 4.

  In this embodiment, since the use area is doubled in the LUT 2, the 8-bit-10-bit control table is virtually used as 8-bit-11 bits in the detected range. Become. However, since the memory capacity of the LUT 2 is not actually increased, it is possible to improve the gradation reproducibility without increasing the memory capacity.

  On the other hand, the amplification factor in the amplification unit 4 is calculated based on the maximum value and use area input to the control unit 6 (step S9), and the calculated amplification factor is output to the amplification unit 4. Here, the amplification factor is calculated by using an expression of (the value of the output signal with respect to the maximum value of the input signal detected by the input signal detection unit 1 / the use area determined in step S5).

  When the image signal output from the digital-analog conversion unit 3 is input to the amplification unit 4, the input image signal is amplified using the amplification factor output from the control unit 6 and input to the amplification unit 4. (Step S10). That is, a value obtained by multiplying the amplitude width input to the normal liquid crystal panel by the amplification factor is obtained.

  Then, the amplified image signal is output from the amplifying unit 4, the output image signal is input to the liquid crystal panel 5, and an image is displayed on the liquid crystal panel 5 with the transmittance based on the input image signal (step S11). ), The relationship between the input image signal and the transmittance of the liquid crystal panel is very close to the complete linearity shown in FIG.

  Note that the image signal detected by the input signal detection unit 1 may specify a detection range in which, when a caption is included in the image source, the maximum value detection process is not performed for a portion including the caption. .

  Moreover, when the minimum value of the input image signal is larger than 0, the minimum value is detected, and the LUT 2 may be controlled by the control unit 6 in the same manner as the above-described processing for detecting the maximum value.

  Further, when there is a problem in the amplification variable time of the amplification unit 4 when changing the amplification factor of the signal displayed on the liquid crystal panel 5 by the amplification unit 4, the frame memory is mounted to store the image. It may be a thing.

  1 may be incorporated in a liquid crystal display that displays an image or a liquid crystal projector that presents an image on a screen or the like.

  Furthermore, the present invention can be used for both normally black liquid crystals whose transmittance increases as the drive voltage increases and normally white liquid crystals whose transmittance decreases as the drive voltage increases.

It is a figure which shows one Embodiment of the image reproduction apparatus of this invention. It is a sequence diagram for demonstrating the image reproduction method in the image reproduction apparatus shown in FIG. It is a figure which shows the relationship between the input signal whose maximum value detected in the preset detection range is 128, and the output signal correct | amended by LUT which is not controlled by the control part with respect to the said input signal. . It is a figure which shows the relationship between the input signal whose maximum value detected in the preset detection range is 128, and the output signal correct | amended by the LUT controlled by the control part with respect to the said input signal. . FIG. 4 is an enlarged view of a portion A shown in FIG. 3. It is a figure which shows a mode that the value of the output signal shown in FIG. 5 was doubled. The figure which shows the mode of control with respect to an output signal when the value of an output signal is not the same between the input signals before and after, and the value of the next output signal is the same in a plurality of consecutive input signals. is there. It is a figure which shows the mode of control with respect to an output signal in case the difference with the value of the output signal which changes next is four. FIG. 7 is an enlarged view of a portion C shown in FIG. 4 and is controlled by the control unit described in FIG. 6. FIG. 4 is an enlarged view of a portion B shown in FIG. 3. It is an enlarged view of the part of D shown in FIG. It is a figure which shows the drive voltage-transmittance characteristic peculiar to a liquid crystal panel. It is a figure which shows the relationship between an input image signal and the transmittance | permeability when an input image signal is converted using LUT. It is a figure which shows the relationship between the input signal and output signal in LUT.

Explanation of symbols

1 Input signal detector 2 LUT
3 Digital / Analog Conversion Unit 4 Amplification Unit 5 Liquid Crystal Panel 6 Control Unit 100 Image Reproduction Device

Claims (7)

An image reproduction device for displaying an image on a liquid crystal panel based on an image signal,
A contrast table for associating a drive signal for displaying an image on the liquid crystal panel with the image signal;
Digital-analog conversion means for converting the image signal output from the comparison table into an analog video signal and outputting the analog video signal;
Amplifying means for multiplying the video signal output from the digital-analog converting means by an amplification factor;
Input detection means for detecting a maximum value or a minimum value within a predetermined time of the image signal;
Based on the maximum value or minimum value of the image signal detected by the input signal detection means, the stored contents of the contrast table are rewritten , and the drive voltage output to the liquid crystal panel rewrites the stored contents of the contrast table. image reproducing apparatus and a control means to change the amplification factor of said amplifying means so as to be substantially the same voltage as after previous rewriting. The image reproduction device according to claim 1,
The control means is configured so that the output range of the image signal uses all areas of the comparison table based on the maximum value or the minimum value of the image signal detected by the input signal detection means. An image reproduction device characterized by rewriting stored contents. In the image reproduction device according to claim 1 or 2,
Wherein the control table image reproduction apparatus according to claim Rukoto is stored smoothing process has been applied value. A liquid crystal display comprising the image reproduction device according to claim 1. A liquid crystal projector comprising the image reproduction device according to claim 1. An image reproduction method using a contrast table that stores a drive signal for displaying an image on the liquid crystal panel in an image reproduction device that displays an image on a liquid crystal panel based on an image signal in association with the image signal,
A process of converting an image signal output from the comparison table into an analog video signal;
A process of multiplying the converted analog video signal by an amplification factor;
A process for detecting a maximum value or a minimum value in a predetermined time of the image signal;
Processing to rewrite the stored contents of the comparison table based on the detected maximum value or minimum value of the image signal ;
An image reproduction method comprising: changing the amplification factor so that the drive voltage output to the liquid crystal panel becomes substantially the same voltage before and after rewriting the stored contents of the comparison table . The image reproduction method according to claim 6,
An image reproduction method according to claim 1, wherein the stored contents of the comparison table are rewritten based on the detected maximum value or minimum value so that an output range of the image signal uses all areas of the comparison table.

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