JP2004272275A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a feeling of visual contrast while evading black floating interference, to reproduce glossy and high-quality videos and to provide videos of screen luminance optimum to an observer with respect to a video display device for displaying video signals. <P>SOLUTION: The picture display device is provided with an average luminance detection part 15 for detecting the average luminance of an input video to correct the luminance of a screen in accordance with the average luminance of the video to be displayed and a peak detection part 16 for detecting the peak state of the video and correcting the luminance of the screen in accordance with the peak state. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an image display device that displays a video signal, and more specifically, has a light source, and dynamically adjusts the brightness of the light source according to the video signal to be displayed. It relates to a display device.

  As a transmission type image display device having a light source means, there is a liquid crystal image display device. Since the transmission type image display device is a non-light emitting type in which the liquid crystal panel itself does not emit light, a light source is separately required. In a direct-view type liquid crystal image display device, a light irradiator called a backlight is provided on the back of a liquid crystal panel, and a fluorescent tube called a cold cathode tube is generally used as a light source. In a projection type liquid crystal image display device commonly called a liquid crystal projector, the brightness of the screen projected on the screen is obtained from a lamp light source such as a halogen lamp or a metal halide lamp.

  FIG. 15 shows a configuration of a general direct-view type liquid crystal image display device. In FIG. 15, 201 is a liquid crystal display unit, 202 is a backlight, 203 is a backlight control unit, 204 is a display control unit, and 205 is an input. From the input 205, a video signal to be displayed on the liquid crystal display unit 201 is input, for example, in the form of a YPbPr signal (luminance signal and color difference signal). The display control unit 204 performs control for displaying the input video signal on the liquid crystal display unit 201. Specifically, processing such as converting the YPbPr signal into RGB signals, rearranging video signals according to the driving method of the liquid crystal display unit 201, and performing optimal gamma correction for the liquid crystal display unit 201 are performed. The backlight 202 is a light source for the liquid crystal display unit 201 to obtain luminance. The backlight control unit 203 controls driving of the backlight 202. The backlight control unit 203 performs control so that the backlight 202 always emits light with a certain luminance. The backlight control unit 203 may have a dimming function. The dimming-capable backlight control unit has a plurality of types of set voltage values (or current values) for obtaining a predetermined light emission luminance, and, for example, receives a command from a microcomputer or the like and switches the set values appropriately. The luminance of the backlight 202 is switched.

  FIG. 16 is a diagram showing the relationship between the average luminance level of the video signal to be displayed and the screen luminance of the image display device. 2 illustrates two types of screen luminance settings as dimming control. Characteristic 16-1 is a user setting, which is a characteristic in the case of backlight dimming when the observer selects the "bright" mode, and the screen luminance obtained when displaying white on the liquid crystal is 420 candela. . Characteristic 16-2 is a characteristic in the case of backlight dimming when the "standard" mode is selected, and the screen luminance obtained when displaying white on the liquid crystal is 260 candela. As is apparent from FIG. 16, the observer who observes the image display device by the dimming function can change the screen brightness. However, this change in the brightness always has a constant brightness regardless of the video signal displayed on the image display device. It is.

  The screen brightness (brightness) of the image display device is determined by the product of the transmittance of the liquid crystal display unit 201 and the emission brightness of the backlight 202. As described above, since the luminance of the backlight 202 is constant regardless of the video signal, the gradation of the video signal to be displayed follows only the transmittance of the liquid crystal display unit 201. That is, it can be said that the display capability of the image display device is determined by the dynamic range (display capability of each brightness of white and black) that the liquid crystal display unit 201 can display.

  In recent years, various improvement methods for dynamically adjusting the contrast of a video signal and the brightness of a light source according to a video signal that changes from time to time have been proposed in order to improve the image quality of a liquid crystal image display device or make it easier to see. ing.

  As a conventional improvement method for dynamically adjusting the brightness of the backlight, there is a method disclosed in Patent Document 1, for example. FIG. 17 shows a conventional improvement method disclosed in Patent Document 1. FIG. 17 is characterized by having an average luminance detection circuit 206 and a backlight control unit 207. The average luminance detection circuit 206 detects the average luminance level of the video signal. When the detected average luminance level is high, the backlight control unit 207 controls the backlight 202 so as to reduce the luminance of the backlight. FIG. 18 shows the relationship between the average luminance and the screen luminance at this time. With these processes, the display luminance is controlled according to the average luminance level of the video signal, so that the observer of the image display device can effectively sense that the displayed video is too bright or conversely too dark. The screen can be displayed easily. Also, the visual dynamic range appears to be expanded as compared with the case where the backlight always emits light with a constant luminance. That is, sharpness is obtained when the screen is dark and bright. Further, in an image in which a bright portion such as a metal image exists in a part of a dark background, the luminance of the metal portion is increased, so that a high-definition image with an increased glossiness can be reproduced.

  Further, as an improvement method for dynamically controlling both the contrast adjustment of the video signal and the brightness adjustment of the backlight with a correlation, for example, a method disclosed in Patent Document 2 is known. In the conventional improvement method disclosed in Patent Document 2, the dynamic range of the video signal is expanded based on the average luminance, and the video signal is level-shifted according to the offset. In this state, the visual luminance level on the screen shifts, and this is absorbed by the dimming of the backlight. Through these processes, the visual sense of contrast is improved.

  Patent Document 3 discloses another improvement method for dynamically controlling both the contrast adjustment (amplitude modulation) of a video signal and the brightness adjustment (light output modulation) of a backlight (light source) with a correlation. There are things that are. In the conventional improvement method disclosed in Patent Document 3, the dark level of a video signal is detected, and when the dark level period exceeds a predetermined threshold, the light output level of the light emitting unit is reduced. At the same time, the dynamic range of the video signal is expanded. If the dark level does not exceed the threshold, neither the light output nor the video signal is modulated. With these processes, the display unevenness at the dark level is not noticeable without affecting the display at the light level.

  However, the improvement method of increasing the luminance of the backlight when the average luminance level of the video signal is low as in Patent Document 1 described above has the following problems. That is, in the liquid crystal display unit 201, a phenomenon called so-called black floating occurs in which light from the backlight leaks even when displaying black. Due to this black floating phenomenon, the image becomes whitish as a whole and the image quality is significantly impaired. For this reason, as the luminance of the backlight increases, the floating of black due to light leakage or the like increases, and the increase in the luminance of the light source is not necessarily reflected in the improvement of the contrast.

  Further, the improvement method of expanding the dynamic range of a video signal as described in Patent Document 2 has the following problem. In other words, if the dynamic range of a signal containing a video whose gradation is collapsed is expanded, the collapsed portion is emphasized and recognized as an obstruction by the observer. When noise is superimposed on the video signal, the noise component is emphasized by the expansion of the dynamic range, and the noise component is also obstructed and recognized by the observer.

Further, as described in Patent Document 3 described above, the improvement method of performing modulation by linking the video signal and the light output of the light source by detecting the dark level period of the video signal has the following problem. In other words, the modulation of the light output of the video signal and the light source is performed only with the dark level information of the video signal, and the information of other video signals (for example, average luminance) is not referred to. The effect of improving the image quality is not exhibited for a video in which there is no. Further, similarly to the above-mentioned Patent Document 2, the amplitude modulation of the video signal promotes the loss of gradation and the disturbance of noise superimposed on the video signal.
JP-A-8-201812 (name "Liquid crystal display device") JP-A-2001-27890 (name "Image display device and image display method") Japanese Patent Application Laid-Open No. 6-102484 (name "Video display device and video display device using spatial light modulator")

  The present invention improves the visual contrast while avoiding disturbances such as expansion of the dynamic range of a video signal and avoiding black floating disturbances. It is an object of the present invention to reproduce and provide an image having an optimum screen luminance to an observer.

  The image display device according to the present invention includes the following technical means in order to achieve the above object.

  That is, the image display device according to the present invention includes the average luminance detecting means for detecting the average luminance, and the peak detecting means for detecting the peak of the video signal.

  Then, the screen brightness is controlled based on the average brightness of the input video. When the average luminance is low, control is performed so that the screen luminance of the video display means is higher than when the average luminance is high.

  The dynamic control of the screen brightness is further corrected based on the detection result of the peak detecting means. When the image displayed by the image display means has a peak that satisfies a certain condition or has a large number of peaks, control is performed so that the screen luminance of the image display means is higher than when there are no or few peaks. When the peak does not exist or is small, control is performed so that the screen luminance of the image display unit is lower than when the peak is present or large.

  The dynamic control of the screen luminance has a characteristic change point corresponding to a certain average luminance value. When the average luminance detected by the average luminance detecting means is equal to or less than the characteristic change point, the characteristic switching based on the peak is performed to control the light source luminance. If the average luminance is equal to or higher than the characteristic change point, the light source luminance is controlled without switching based on the peak.

  That is, according to the present invention, in addition to performing the same light source control as the conventional example, the light source luminance is dynamically controlled in accordance with the peak of the displayed image.

  Specifically, for example, in an image in which the average luminance of a video signal to be displayed is low, that is, in an image that is dark as a whole and has no or few peaks, an increase in screen luminance increases the luminance of black of the image display unit. It simply increases the so-called black float interference. Therefore, in an image in which the entire screen is dark, that is, an image having a low average luminance value and having no peak or a small peak, the light source luminance is corrected to decrease. This avoids black floating interference.

  Also, for example, in an image in which the average luminance of a video signal to be displayed is low, that is, in an image that is dark as a whole and has many or many peaks, it is better to increase the luminance at the peak portion of the image to emphasize the sharpness and stereoscopic effect. In this case, the screen brightness is increased because a sensed image can be displayed. An image in which a metal such as a ring is displayed in a dark background corresponds to the image, and the luminance of the light source is sufficiently increased to express the glossiness of the metal.

  In addition, since the process of expanding the dynamic range of the video signal is not performed, interference such as loss of gradation and enhancement of noise components does not occur.

  In addition, since information on whether the image is bright or dark is obtained from the detection of the average luminance as well as the presence or absence of the peak of the display image, not only the dark image but also a dark image (an image having a low average luminance value) and a bright image are obtained. Dynamic contrast is improved by switching images (images having a high average luminance).

  As described above, according to the present invention, it is possible to provide an optimal display image to an observer.

  In the present invention, the backlight (light source) is dynamically controlled by the average luminance. That is, the backlight luminance is reduced for a video having a high average luminance (bright), and the backlight luminance is increased for a video having a low average luminance (dark). Compared with a conventional case where a backlight emits light at a constant luminance, it is possible to prevent a viewer from feeling uncomfortable when a bright image is too bright or a dark image is too dark. Also, switching between a dark image and a bright image adds sharpness, and can enhance visual contrast.

  Further, in the present invention, the control characteristics of the backlight (light source) are dynamically corrected based on the peak value of the image to be displayed. In the case of a dark image without a peak, that is, when the peak of the display image is equal to or less than a certain condition and the average luminance level is low, the increase in the backlight luminance merely causes the so-called black floating interference in which the black luminance of the liquid crystal display increases. It just increases it. Therefore, in an image having a low average luminance and having no peak value or an image having a small peak value, dynamic correction is performed so as to suppress an increase in backlight luminance. Thereby, it is possible to express glossiness while avoiding black floating interference.

  Furthermore, according to the present invention, when it is determined that there is a peak or a large number of peaks in an overall dark image, the luminance of the backlight is increased. In an image in which a metal such as a ring is displayed in a dark background, the brightness of the backlight is sufficiently increased to express the glossiness of the metal. Thereby, it is possible to express glossiness while avoiding black floating interference.

Further, in the present invention, since the process of expanding the dynamic range of the video signal is not performed, interference such as loss of gradation and enhancement of noise components does not occur.
In general, according to the present invention, it is possible to provide an optimal display image to an observer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First embodiment>
First, an image display device according to a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram showing a configuration of an image display device according to a first embodiment of the present invention. As shown in FIG. 1, a liquid crystal display unit 11, a backlight 12, a backlight control unit 13, a display control unit 14, an average luminance detector 15, a peak detector 16, and an input 17.

  From the input 17, a PIC (Picture) signal which is a video signal to be displayed on the liquid crystal display unit 11 is input in the form of, for example, a Y color difference signal. The display control unit 14 performs control for displaying the PIC signal on the liquid crystal display unit 11 and outputs the PIC signal to the liquid crystal display unit 11 as a DRV (Drive) signal. The backlight 12 is a light source for the transmissive liquid crystal display unit 11 to obtain screen brightness.

  The average luminance detecting unit 15 detects the average luminance of the PIC signal and outputs the average luminance to the backlight control unit 13 as an AVE (Average) signal. The average luminance is expressed as a percentage. When the displayed image is entirely black on the entire screen, the average luminance is 0%. In the case of all of the highest values of white, the average luminance is 100%. The backlight control unit 13 receives the AVE signal, and controls the brightness of the backlight 12 with a CTL (Control) signal. The characteristics of the control are such that if the AVE signal is large, the brightness of the backlight is reduced, and if the AVE signal is small, the brightness of the backlight is increased.

  The feature of the image display device of the present invention resides in that the image display device includes the peak detection unit 16. The PEK (Peak) signal output from the peak detection unit 16 is also passed to the backlight control unit 13 like the AVE signal.

  FIG. 2 is a detailed block diagram of the peak detector 16. In FIG. 2, 21 is a comparator, 22 is a counter, 23 is a discriminator, 24 is a threshold m generator, 25 is a threshold n generator, 26 is a V reset S, 27 is a V reset E, 28 is an input, and 29 is an input. Output.

  A PIC signal is input from an input 28 and input to the comparator 21. The comparator 21 compares the luminance signal or the luminance component of the sequentially input PIC signal with the threshold m generated by the threshold m generator 24, and outputs the comparison result to the counter 22 as a CMP (Compare) signal. The CMP signal takes a High state when the input luminance signal level is larger than the threshold value m, for example, and takes a Low state when the input luminance signal level is smaller than the threshold value m. The V reset S26 generates a V-ST (Vertical-start) signal pulse according to the vertical start phase of the video signal. The V reset E27 generates a V-END (Vertical-end) signal pulse according to the vertical end phase of the video signal. The vertical start and vertical end of the video signal are defined, for example, by the rise and fall of a vertical synchronization signal accompanying the PIC signal. The counter 22 performs a counting operation in a period defined by the V-ST signal and the V-END signal. The counter value is reset by the V-ST signal. When the CMP signal is High, that is, when the luminance level of the PIC signal is larger than the threshold value m, the up-count operation of +1 is performed, and when the CMP signal is Low, the counter value is held. Then, the counter value is latched and determined by the V-END signal, and is output to the discriminator 23 as a CNT (Count) signal. The discriminator 23 compares the CNT signal determined by the V-END signal with the threshold value n of the threshold value n generator 25 and outputs the result from the output 29 as a PEK signal. The state of the PEK signal is, for example, High when the value of the CNT signal is larger than the threshold value n, and Low when the value of the CNT signal is smaller than the threshold value n.

  The peak detection unit 16 performs the above-described series of operations on all the pixels in the screen during the period defined by the V-ST signal and the V-END signal. Assuming that the PIC signal is a signal of VGA resolution, the number of counts in a series of operations is about 300,000 (= 640 * 480). Here, it is assumed that the PIC signal is an 8-bit digital signal. Therefore, the brightness level of the PIC signal is, for example, 0 for black and 255 for white, which is the highest value. It is also assumed that threshold value m is 200 and threshold value n is 300. First, the count value of the counter 22 is reset to 0 by the V-ST signal. In the comparator 21, the luminance level of the sequentially input PIC signal is compared with the threshold value m (= 200) on a pixel-by-pixel basis, and when it is equal to or greater than m (= 200), the comparator 21 sends a High signal to the counter 22. , The counter 22 counts up by +1. If m (= 200) or less, the comparator 21 sends a Low signal to the counter 22, and the counter 22 holds the count value and does nothing. Then, the result of the counter 22 is sent to the discriminator 23 by the V-END signal. The discriminator 23 determines whether the result of the counter 22 is larger or smaller than a threshold value n (= 300). In other words, the video signal of one screen from the video start to the end specified by the vertical synchronization is compared with the threshold value m for each pixel in the order of input, and the number of pixels at the level higher than the threshold value m is counted. If it is n or more, it is determined that there is a peak from the determination that there are n or more pixels of level m or more on a 300,000 pixel screen, and the result is output.

  The up-counting by the counter 22 may be performed not every pixel but every d pixels (d is an arbitrary integer), in which case the processing operation speed (clock speed) can be reduced to 1 / d. It is. In some cases, peak detection can be sufficiently performed even every other line. Here, the line indicates a vertical scanning unit when the PIC signal is displayed on the liquid crystal display unit 11.

  Also, the case where the threshold value m is 200 and the threshold value n is 300 has been described. However, m = 255, that is, a pixel having the maximum amplitude level in an image may be detected. When n = 1, that is, when only one of the images exceeds the threshold value m, it may be determined that there is a peak.

Next, the operation of the backlight control unit 13 will be described with reference to FIG. FIGS. 3A and 3B are diagrams illustrating control characteristics of the backlight control unit 13. FIG. In FIG. 3A, the horizontal axis is the average luminance (%) detected by the average luminance detection unit 15, and is 0% when the screen is all black and 100% when the screen is all white. The vertical axis represents the screen luminance (candela, cd / m ²⁾ as a result of the liquid crystal display unit 11 displaying white (255 levels of an 8-bit digital signal) being irradiated on the backlight 12 controlled by the backlight control unit 13. ). Since an average luminance of 0% means that all display areas display 0 level black, the expression of luminance when displaying 255 levels of white when the average luminance is 0% is strictly contradictory. For the sake of simplicity, the case where the average luminance is almost 0% is expressed as 0%. For example, at the VGA resolution, the average brightness when displaying 255 levels of white in an area of 20 pixels × 20 pixels while the entire screen displays 0 levels of black is 0.13%. Expressed as an average luminance of 0%. FIG. 3B is a diagram showing data (numerical values) of the characteristic diagram shown in FIG. This embodiment is characterized in that there are two types of characteristics of the average luminance and the screen luminance. FIG. 3A has two characteristics, a characteristic 3-1 and a characteristic 3-2. These two characteristics are switched by a PEK signal which is a detection result of the peak detection unit 16.

  In FIG. 3A, a point at which the average luminance is 40% is a characteristic change point at which the control characteristic is switched, and whether the average luminance is higher or lower than this point (whether or not the average luminance exceeds this point) is determined. The control characteristics of the light 12 are switched. In FIG. 3A, switching is performed according to the PEK signal, and when the PEK signal is High (the peak detection unit 16 has determined that the display image has a peak), the characteristic 3-1 in FIG. 3A is selected. The backlight 12 is controlled so that the screen luminance shown by this characteristic diagram is obtained. That is, for example, when the average luminance is as low as 20%, the backlight 12 is controlled so that the screen luminance is obtained at 440 candelas. On the other hand, when the average luminance is as high as 70%, control is performed so that a screen luminance of 290 candela is obtained. When there is no peak portion in the video, the backlight 12 is controlled by selecting the characteristic 3-2 in FIG. 3A according to the low level of the PEK signal. Even with the same average luminance detection result (for example, an average luminance of 20%), the backlight 12 is corrected such that the peak is 440 candela when there is a peak and 390 candela when there is no peak.

  In FIG. 3A, when the image has no peak portion, correction is performed so as to take a lower luminance value than when it is determined that there is a peak. In addition, this correction is controlled so as to take a luminance value higher than the luminance when the average luminance detection value is high.

  With this control, when the image displayed on the liquid crystal display unit 11 has a peak, the backlight is lit more on a dark screen than on an average bright screen to obtain screen brightness. For example, for a screen having a metal image such as a spoon in a dark background, the glossiness of the metal part is expressed by increasing the screen luminance. In an average bright image such as a clear sky, lowering the screen brightness improves the sense of visual contrast in a scene change between a spoon scene and a blue sky scene. In the case of an image without a peak, there is no or little image of high luminance for which a glossy feeling is desired. In this case, even if the backlight is turned on, energy is blocked by the liquid crystal display unit 11 and wasted wastefully. The lift is also noticeable. Therefore, in FIG. 3A, the characteristic 3-1 is corrected to the characteristic 3-2 that suppresses the increase in luminance, and is controlled.

  Also, for example, when compared with the characteristics of the conventional example of FIG. 16 in which the screen luminance is uniformly illuminated at 420 candela, the characteristics of FIG. This is advantageous in terms of power consumption as compared with the characteristic 16-1.

  The hardware for obtaining the characteristics shown in FIG. 3A may be realized by, for example, a look-up table using a ROM, or may be realized in the LSI by a broken line approximation operation.

  FIG. 3A shows an example in which the screen luminance is linearly controlled with respect to the average luminance. However, for example, as shown in FIGS. 4A and 4B, the screen luminance may be controlled with non-linear characteristics. .

  Further, FIG. 3A shows an example in which the characteristic change point is 40%, but the characteristic change point is a point at 50% of the average luminance as shown in FIGS. 4A and 4B. In some cases, the value of the average luminance serving as the characteristic change point is arbitrary.

  FIG. 3A shows an example of the characteristic of 200 candela when the average luminance is 100%, and the characteristic of the screen luminance 500 candela when the average luminance is 0% and there is a peak, for example, FIGS. 5A and 5B. As shown in the figure, the screen luminance may be 100 candela when the average luminance is 100% and the screen luminance is 350 candela when the average luminance is 0% and there is a peak. The relationship between the average luminance and the screen luminance depends on the characteristics of the liquid crystal display unit 11 and the characteristics of the backlight 12, and the characteristics of the liquid crystal display unit 11, the evaluation results obtained by actually evaluating the display screen, or the consumption What is necessary is just to determine the best value in consideration of electric power and the like, and control the backlight controller 13.

  As described above, the image display device according to the present embodiment includes the liquid crystal image display unit, the backlight, the backlight control unit, the display control unit, the average luminance detection unit, and the peak detection unit. This is an image display device that dynamically controls the luminance of the backlight according to the peak.

  That is, in the present embodiment, the backlight is dynamically controlled based on the average luminance of the image to be displayed, and the control characteristics are corrected based on the peak value. That is, for example, in the case of a dark image having no peak, that is, when the peak of the display image is equal to or less than a certain condition and the average luminance level is low, the increase in the backlight luminance increases the black luminance of the image display means, so-called black floating. Since the interference is merely increased, in a video having a low average luminance and no peak value or a video having a small peak value, correction is performed so as to suppress an increase in backlight luminance. In addition, dynamic contrast is improved by switching between a dark image (an image having a low average luminance value) and a bright image (an image having a high average luminance).

  Thereby, it is possible to express glossiness while avoiding black floating interference, and to provide an optimal display image to an observer.

<Second embodiment>
Next, an image display device according to a second embodiment of the present invention will be described with reference to FIGS.

  FIG. 6 is a block diagram of the peak detection unit 16 in the image display device according to the second embodiment of the present invention. In FIG. 6, components equivalent to those in FIG. 2 described above are denoted by the same reference numerals. In FIG. 6, 61, 62, 65, and 66 are comparators, 63 and 64 are counters, 67 is a discriminator, 68 to 71 are threshold generators that generate thresholds ma, mb, na, and nb, respectively, and 72 is an output. It is.

  A PIC signal is input from an input 28 and input to comparators 61 and 62, respectively. The comparator 61 compares the luminance signal or the luminance component of the sequentially input PIC signal with the threshold ma generated by the threshold ma generator 68, and outputs the comparison result to the counter 63. The counter 63 performs a counting operation in a period defined by the V-ST signal and the V-END signal, and outputs a result to the comparator 65. The comparator 65 compares the output of the counter 63 with the threshold value na of the threshold value na generator 70 and outputs the result to the discriminator 67 as a CMP-A signal.

  The comparator 62 compares the luminance signal or the luminance component of the sequentially input PIC signal with the threshold mb generated by the threshold mb generator 69, and outputs the comparison result to the counter 64. The counter 64 performs a counting operation in a period defined by the V-ST signal and the V-END signal, and outputs a result to the comparator 66. The comparator 66 compares the output of the counter 64 with the threshold nb of the threshold nb generator 71 and outputs the result to the discriminator 67 as a CMP-B signal.

  The discriminator 67 receives the CMP-A signal and the CMP-B signal, calculates a MOD signal as a peak detection value in three steps from both signals, and outputs the MOD signal from an output 72.

  This embodiment differs from the first embodiment in that it has two sets of peak detecting means having different thresholds and detects the degree of the peak level of the video signal in three stages. From the peak level and the frequency of appearance, the MOD (Mode) signal takes on three levels of values of "no peak", "slight peak", and "many peaks". This MOD signal is output to the backlight control unit 13.

  For example, assume that ma = 160, mb = 200, and na = nb = 400. Assuming that there are 500 pixels of the luminance level 230 in one screen of the PIC signal, the comparator 65 and the comparator 66 each determine that “there is a peak”. Output as "many peaks".

  Also, for example, it is assumed that there are 500 180-level pixels and 100 230-level pixels in one screen of the input video luminance signal. In this case, the comparator 65 determines that there is no peak, and the comparator 66 determines that there is a peak. Therefore, in this case, the discriminator 67 sets the MOD signal to “a little peak” and outputs the signal.

  Also, for example, it is assumed that there are 500 100-level pixels and 100 180-level pixels in one PIC signal screen. In this case, both the comparator 65 and the comparator 66 determine that there is no peak. Therefore, in this case, the discriminator 67 outputs the MOD signal as “no peak”.

  FIGS. 7A and 7B are diagrams showing the control characteristics of the backlight control unit 13 in the present embodiment. In FIG. 7A, the horizontal axis is detected by the average luminance detection unit 15. The average brightness is shown, and the vertical axis is the screen brightness of the liquid crystal display unit 11 as a result of irradiation by the backlight 12.

  As is clear from FIGS. 7A and 7B, the backlight control unit 13 in the second embodiment has three characteristics. These three different characteristics are switched by the MOD signal that is the detection result of the peak detection unit 16 described with reference to FIG. Specifically, when the MOD signal is in a state of “many peaks”, the characteristic 7-1 is selected and the backlight 12 is controlled. If the state is "slightly peaked", the characteristic 7-2 is selected. If there is no peak, the characteristic 7-3 is selected. Compared to the configuration of the first embodiment in which switching is performed by binary detection, in the present embodiment, it is possible to perform finer control.

  Note that, in the above example, an example in which the presence / absence of a peak is detected in three states and three control characteristics are provided is described. However, the presence / absence of a peak is detected in four or more states, and the number of detected states corresponds to the number. Control characteristics may be provided.

  As described above, in the present embodiment, more ideal processing can be performed by detecting a plurality of states by peak detection and providing control characteristics for the number of the peak detection states.

<Third embodiment>
Next, an image display device according to a third embodiment of the present invention will be described with reference to FIG.

  FIG. 8 is a block diagram showing the configuration of the peak detection unit 16 in the image display device according to the third embodiment of the present invention. In FIG. 8, the same components as those in FIG. is there. In FIG. 8, 81 and 83 are comparators, 82 is a latch, and 84 is a threshold p generator.

  The feature of this embodiment is that the comparator 81 forms a loop and detects the maximum luminance level in the displayed image. That is, an FBK (Feedback) signal as a comparison result is fed back to the input of the comparator 81. The feedback operation of the comparator 81 is performed in units of pixels of the PIC signal sequentially input, and the levels of the PIC signal and the FBK signal are compared, and the larger signal is output as an updated FBK signal.

  At the time of starting the image processing of the PIC signal, which is the start of the processing of the comparator 81, the FBK signal is reset to zero according to the V-ST signal output from the V reset S26. For example, it is assumed that a PIC signal is input in the order of pixels a0, a1, a2, and a3 in order from the video start, and the levels are a0 = 50, a1 = 200, a2 = 140, and a3 = 50, respectively. Since the FBK signal is reset to zero at the start of the video, the comparator 81 compares a0 with zero and outputs 50 (= a0) as the FBK signal at the time of inputting the first pixel a0. At the time when the next pixel a1 is input, a1 is compared with the FBK signal fed back, so that the levels of a0 and a1 are substantially compared, and the level of the FBK signal to be updated is 200 (= a1). In the next time, since the comparison is made between a2 and the FBK signal fed back, the FBK signal is larger and the FBK signal is maintained at 200. The FBK signal is maintained at 200 in comparison with a3 at the next time. In this way, the comparison processing is sequentially performed on the input in pixel units, and the information of the maximum level among the pixels input from the start of the vertical image is detected. This operation is repeated until the end of the vertical image, and the maximum level is detected within one screen.

  The latch 82 captures the operation result of the comparator 81 at the timing of the end of the vertical image, and outputs the result to the comparator 83. The comparator 83 compares the threshold value p from the threshold value p generator 84 with the output of the latch 82. If the output level of the latch 82 is larger than the threshold value p, it is determined that “there is a peak”, and the result is determined by PEK. The signal is output from the output 29 to the backlight control unit 13 as a signal. The backlight control unit 13 controls the backlight 12 by switching the above-described characteristics of FIG. 3 using the PEK signal.

  As described above, in the present embodiment, the maximum level in the video to be displayed is detected by sequentially comparing the input signal with the past maximum level on a pixel basis in a loop. The comparison operation is performed for one screen from the vertical video start to the vertical video end of the input video signal. In the present embodiment having such a configuration and operation, as compared with the peak detection of the first embodiment, the circuit scale is reduced and power consumption is also advantageous because the counter can be omitted. Also, only one threshold value is required for management, and system adjustment is facilitated.

<Fourth embodiment>
Next, an image display device according to a fourth embodiment of the present invention will be described with reference to FIG.

  FIG. 9 is a block diagram showing the configuration of the peak detection unit 16 in the image display device according to the fourth embodiment of the present invention. In FIG. The same reference numerals are given. In FIG. 9, 91 and 92 are comparators, 93 is a discriminator, 94 and 95 are threshold generators for generating thresholds pa and pb, respectively, and 96 is an output.

  The feature of the present embodiment is that the output of the latch 92 is compared with two types of threshold values pa and pb, and three types of peak states are detected, and a “peak is small” and a “peak is small” as a PMOD (Peekmode) signal. The information of “intermediate level” and “large peak” is output from the output 96 to the backlight control unit 13.

  For example, assume that pa = 200 and pb = 150. When the output of the latch 82 is at the 230 level, both the comparators 91 and 92 determine that "there is a peak". Therefore, the discriminator 93 determines that “the peak is large”.

  For example, when pa = 200, pb = 150, and the output of the latch 82 is at the 160 level, the comparator 91 outputs a result “no peak” and the comparator 92 outputs “peak”. Output the result. Therefore, the discriminator 93 determines that “the peak is at an intermediate level”.

  Further, for example, when pa = 200 and pb = 150 and the output of the latch 82 is at the 100 level, both the comparators 91 and 92 output a result indicating "no peak". Therefore, the discriminator 93 determines that “the peak is small”.

  The backlight control unit 13 receives the PMOD signal, and performs three-stage backlight control using the characteristics of FIGS. 7A and 7B. If the PMOD signal is “large in peak”, the characteristic 7-1 is selected. The characteristic 7-2 is selected when the peak is at the intermediate level, and the characteristic 7-3 is selected when the peak is small.

  In the above example, an example in which the peak level is detected in three states and three control characteristics are provided, but the peak level is detected in four or more states and the number of detected states corresponds to the number of detected states. Control characteristics may be provided.

  As described above, in the present embodiment, more ideal processing can be performed by detecting the peak detection described in the third embodiment as a plurality of states from a plurality of thresholds and controlling the backlight. It becomes possible.

<Embodiment 5>
Next, an image display device according to a fifth embodiment of the present invention will be described with reference to FIG.

  FIGS. 10A and 10B are diagrams showing control characteristics of the backlight control unit 13 of the image display device according to the fifth embodiment of the present invention. In FIG. 10A, the horizontal axis represents the average luminance (%) detected by the average luminance detection unit 15, and the vertical axis represents the screen luminance of the liquid crystal display unit 11 as a result of irradiation by the backlight 12.

  A feature of the present embodiment is that a threshold value is set, and in a certain range, the screen luminance is controlled to a constant value regardless of the average luminance. FIGS. 10A and 10B show a case where the threshold value ra on the lower side of the average luminance is 20%. When the detected average luminance is 20% or less, the screen luminance is constant regardless of the average luminance. When the peak is detected by the peak detection unit 16, the screen luminance is 500 candela, and no peak is detected. The screen brightness in this case is 400 candela. Also, the threshold rb on the higher average luminance side is 80%. When the detected average luminance is 80% or more, the screen luminance is a constant value regardless of the average luminance, and the screen luminance is 200 candela regardless of the detection result of the peak detection unit 16.

  This is a characteristic that takes into account that, when the average luminance of an image is detected, the frequency of occurrence of detection results generally equal to or less than the threshold value ra or equal to or greater than the threshold value rb is low. The low frequency part is a fixed value, and the dynamic range of the backlight is used effectively in the high frequency part.

  In FIGS. 10A and 10B, the thresholds ra and rb are assumed to be 20% and 80%, respectively. However, the threshold ra may be 30%, for example. The threshold rb may be 70%. Alternatively, only the threshold value ra may be made valid (for example, 30%), and the threshold value rb may be made 100%, that is, the characteristic may be made invalid. Alternatively, only the threshold rb may be enabled (for example, 70%), and the threshold ra may be set to 0%, that is, the threshold ra may be disabled.

  As described above, a feature of the present embodiment is that a threshold value is set in the backlight control characteristic so that the screen luminance takes a fixed value regardless of the average luminance in a certain range. The threshold is set on both sides of the average luminance being low and high, or only one of them is set. With this feature, it is possible to effectively use the dynamic range of the backlight in a portion where the detection frequency is high, and to perform optimal control for the displayed image.

<Sixth embodiment>
Next, an image display device according to a sixth embodiment of the present invention will be described with reference to FIGS.

  FIG. 11 is a block diagram showing a configuration of a projection type liquid crystal projector which is an image display device according to a sixth embodiment of the present invention. In FIG. 11, components equivalent to those in FIG. is there. 11, reference numeral 111 denotes a screen, 112 denotes a projection lens, 113 denotes a liquid crystal light valve, 114 denotes a lamp, and 115 denotes a lamp control unit.

  The lamp control unit 115 controls the lamp 114 based on the AVE signal, which is the average luminance signal detected by the average luminance detection unit 15, and the PEK signal detected by the peak detection unit 16. The lamp 114 irradiates the liquid crystal light valve 113 with light under the control of the lamp control unit 115. The liquid crystal light valve 113 is composed of one or three transmissive liquid crystal panels, and modulates the light of a lamp 114 as a light source into each of RGB. The light that has passed through the liquid crystal light valve 113 is magnified by the projection lens 112 and projected on the screen 111 to become a display image.

  FIGS. 12A and 12B show the control characteristics of the lamp 114 in the lamp control unit 115. FIG. In FIG. 12A, the horizontal axis is the average luminance (%) detected by the average luminance detection unit 15, and the vertical axis is the screen 111 of the result of irradiating the lamp 114 controlled by the lamp control unit 115. Screen brightness (lumens). The characteristic 12-1 and the characteristic 12-2 are switched by the PEK signal. That is, when the peak detector 16 determines that there is or has many peaks, the lamp 114 is controlled so as to obtain the screen luminance shown in the characteristic 12-1. If it is determined that there is no or little peak, the lamp 114 is controlled so as to obtain the screen luminance shown in the characteristic 12-2.

  As described above, the image display device of the present invention is suitable for not only a direct-view type liquid crystal display device but also a projection type liquid crystal display device.

<Embodiment 7>
Next, an image display device according to a seventh embodiment of the present invention will be described with reference to FIGS.

  FIG. 13 is a block diagram showing a configuration of an image display device according to a seventh embodiment of the present invention. In FIG. 13, the same reference numerals are given to components equivalent to those in FIG.

  In FIG. 13, reference numeral 101 denotes a video determination unit, which determines the characteristics of an image to be displayed by this processing unit. The determination result is output to the backlight control unit 13 as a P-BRT (Picture-Bright) signal and a P-PEK (Picture-Peak) signal. The P-BRT signal is a signal indicating the degree of brightness of the video signal to be displayed, and is, for example, a detection result obtained by detecting an average luminance value of the video signal to be displayed. The P-PEK signal is a signal indicating the degree of the peak value of the video signal to be displayed, and is obtained, for example, by the processing described in the first embodiment with reference to FIG.

  FIGS. 14A and 14B are diagrams showing control characteristics of the backlight control unit 13 of the image display device according to the seventh embodiment of the present invention. In FIG. 14A, the horizontal axis is the P-BRT signal, and the larger the value, the brighter the displayed image or the higher the average luminance. The vertical axis indicates the brightness (luminance) of the light emitting surface of the backlight 12. For example, if the transmittance of the liquid crystal display unit 11 is 5%, and if the backlight luminance is 2000 candela, the light passes through the liquid crystal display unit 11 and the luminance obtained as a display screen is about 100 candela. is there.

  FIGS. 14A and 14B show two different characteristics. The characteristic 14-1 and the characteristic 14-2 are switched by the aforementioned P-PEK signal. Specifically, when the P-PEK signal is small, the characteristic 14-2 is selected to control the backlight. When the P-PEK signal is large, the characteristic is selected to control the backlight. That is, FIGS. 14A and 14B mean that when the peak is large or large and the screen is dark, the light emission amount of the backlight is further increased. If the peak is small or small and the screen is dark, the amount of light emitted from the backlight is suppressed.

  As described above, in the present embodiment, the backlight (light source) of the backlight (light source) is determined by using the means for detecting whether the image display is darker than the predetermined level or whether the image to be displayed is dark or bright and the image peak detector. Control the amount of light. The characteristic is that when the average level of one screen of video display is darker than a certain value, when the light source is determined to have or has many peaks, the light source is higher than when it is determined to have no or few peaks. Take the luminance value. By the above control, for example, in a scene where fireworks are rising in the night sky, only for an image in which a firework has opened and a bright image has occurred in a dark night sky, in order to sufficiently express the high brightness of the fireworks. And increase the amount of light of the backlight. The presence or absence of fireworks is determined by peak detection. Through these processes, the brightness of fireworks can be sufficiently expressed, and the expanded dynamic contrast can be expressed by a scene change between the fireworks scene (night sky) and the overall bright scene (scene such as audience). Becomes possible.

  As described above, the image display device of the present invention includes a video display unit composed of a direct-view type liquid crystal or a projection type liquid crystal, a display control unit, a light source such as a backlight, and a light source control unit such as a backlight control unit. , An average luminance detecting means and a peak detecting means, and dynamically controlling the luminance of a light source such as a backlight according to the average luminance and the peak of a video to be displayed.

  INDUSTRIAL APPLICABILITY The present invention can be used in a display device or the like that displays an image.

FIG. 2 is a block diagram illustrating a configuration of the image display device according to the first embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of a peak detection unit in the image display device according to the first embodiment of the present invention. FIG. 4 is an explanatory diagram illustrating an example of a control characteristic of a backlight control unit in the image display device according to the first embodiment of the present invention. FIG. 5 is an explanatory diagram illustrating another example of the control characteristics of the backlight control unit in the image display device according to the first embodiment of the present invention. FIG. 5 is an explanatory diagram showing still another example of the control characteristics of the backlight control unit in the image display device according to the first embodiment of the present invention. FIG. 9 is a block diagram illustrating a configuration of a peak detection unit in an image display device according to a second embodiment of the present invention. FIG. 9 is an explanatory diagram illustrating an example of a control characteristic of a backlight control unit in the image display device according to the second embodiment of the present invention. FIG. 13 is a block diagram illustrating a configuration of a peak detection unit in an image display device according to a third embodiment of the present invention. FIG. 15 is a block diagram illustrating a configuration of a peak detection unit in an image display device according to a fourth embodiment of the present invention. FIG. 15 is an explanatory diagram showing an example of a control characteristic of a backlight control section in an image display device according to a fifth embodiment of the present invention. It is a block diagram showing the composition of the image display device concerning a 6th embodiment of the present invention. It is an explanatory view showing an example of control characteristics of a lamp control part in an image display device concerning a 6th embodiment of the present invention. It is a block diagram showing the composition of the image display device concerning a 7th embodiment of the present invention. It is an explanatory view showing an example of control characteristics of a backlight control part in an image display device concerning a 7th embodiment of the present invention. FIG. 3 is a block diagram illustrating a configuration of an image display device according to a conventional technique. FIG. 16 is an explanatory diagram illustrating control characteristics of a backlight control unit included in the image display device in FIG. 15. FIG. 11 is a block diagram illustrating a configuration of an image display device according to another related art. FIG. 18 is an explanatory diagram illustrating control characteristics of a backlight control unit included in the image display device in FIG. 17.

Explanation of reference numerals

11 LCD display
15 Average luminance detector
16 Peak detector

Claims (10)

An image display device that controls screen brightness according to an average brightness of an input video,
With peak detection means for detecting the peak value of the input image or the number of pixels that become the peak,
Regarding the control of the screen luminance, the control unit has a plurality of control characteristics of the screen luminance according to an average luminance of an image, and switches the plurality of control characteristics according to a detection result of the peak detection unit. An image display device for correcting screen brightness. The image display device according to claim 1,
The image display device, wherein each of the plurality of control characteristics has a characteristic of suppressing the screen luminance as the average luminance of the video is higher at least within a predetermined range of the average luminance of the video. The image display device according to claim 1, wherein
When the detection result of the peak detection unit is a state where there is no or few peaks, the control characteristic is switched to a control characteristic of suppressing the screen brightness as compared with a case where there is a peak or a lot of peaks. Image display device. The image display device according to claim 1 or 2,
Regarding the control of the screen luminance, the control characteristic has a characteristic change point corresponding to an average luminance of an image, and when the average luminance of the input image is equal to or less than the characteristic change point, the control characteristic is determined in accordance with a detection result of the peak detecting means. An image display device characterized by switching. The image display device according to claim 4,
When the average luminance of the input image is equal to or less than the characteristic change point, the detection result of the peak detection unit is compared with the case where the peak is present or the case where the peak is present or the case where the peak is large or the case where the peak is small. An image display device characterized in that the characteristic is switched to a characteristic that suppresses the luminance by using the characteristic. An image display device that controls screen brightness according to an average brightness of an input video,
With peak detection means for detecting the peak value of the input image or the number of pixels that become the peak,
Regarding the control of the screen brightness, having a characteristic change point corresponding to the average brightness of the video,
When the average luminance of the input image is equal to or less than the characteristic change point, the detection result of the peak detection unit is compared with the case where the peak is present or the case where the peak is present or the case where the peak is large or the case where the peak is small. An image display device that corrects the screen luminance so as to suppress the screen luminance. In an image display device that controls screen luminance according to the average luminance of an input video,
With peak detection means for detecting the peak value of the input image or the number of pixels that become the peak,
An image display device, wherein the screen luminance is corrected using both the average luminance of the input video and the detection result of the peak detecting means. An image display device that controls screen brightness according to the degree of brightness of an input video,
With peak detection means for detecting the peak value of the input image or the number of pixels that become the peak,
Regarding the control of the screen brightness, it has a plurality of control characteristics of the screen brightness according to the average brightness of the video,
An image display device, wherein the screen brightness is corrected by switching the plurality of control characteristics in accordance with a detection result of the peak detection unit. A screen brightness control method for controlling screen brightness according to an average brightness of an input image,
Detecting the peak value of the input image or the number of pixels that become the peak,
Switching a plurality of control characteristics of the screen luminance according to the average luminance of the image according to a detection result of a peak value of the input image or the number of peak pixels. Method. A screen brightness control method for controlling screen brightness according to an average brightness of an input image,
Detecting the peak value of the input image or the number of pixels that become the peak,
In the case where the average luminance of the input image is equal to or less than the characteristic change point, the peak value or the number of peak pixels of the detected input image is in a state where there is no or few peaks, and in a state where there is a peak or many. And correcting the screen luminance so as to suppress the screen luminance as compared with the case of the image display method.

Images