JP5143959B1 - Video display device and television receiver - Google Patents

Abstract

Provided are a video display device and a television receiver with which the sense of brightness of a light-emitting section can be increased to achieve high-contrast video representation while implementing high-definition video representation in accordance with video genre without ever inducing a sense of incongruity. An area-active control/brightness stretching unit (5) stretches and augments the brightness of a light source in accordance with an input video signal, a light-emission detection unit (2) detects, as a light-emitting section, a superior region in a prescribed range of a histogram of the input video signal, and a mapping unit (3) reduces the brightness of the video signal in non-light-emitting sections, thereby enhancing display brightness of the light-emitting section. During the above, a control curve determining the stretching amount of the brightness of the light source is switched in accordance with input-video-signal genre information detected by a genre-information detection unit (4), thereby modifying the brightness stretching amount and the gain of the video signal in the non-light-emitting sections.

Description

  The present invention relates to a video display device and a television receiver, and more particularly to a video display device and a television receiver having an enhancement function for improving the quality of a displayed video.

  In a video display device, an enhancement function for improving the quality of a displayed video is known. When the enhancement function is executed, the maximum value of the gradation is usually detected for each frame of the video signal, and if the level of the maximum value is low, the video signal in the high gradation part is gained and expanded. Further, the minimum value of the gradation of the video signal is detected, and if the minimum value is high, the gradation is lowered by applying a compression gain to the video signal of the low gradation part. By using such an enhancement function, the signal range of the video signal is widened, the contrast of the displayed image is increased, and the image quality is improved.

  For example, Patent Document 1 discloses a liquid crystal display device that automatically adjusts the contrast so that the brightness of an image is close to that before the adjustment as the brightness of the backlight device is lowered or raised. In this liquid crystal display device, an operator can individually turn on and off a plurality of light sources of the backlight device in order to save power, and an enhancement function works when the brightness of the image changes due to the light source on and off. The contrast of the display image is adjusted according to the brightness.

  Japanese Patent Application Laid-Open No. 2004-228688 describes a feature of an input video signal according to the genre of video displayed on a liquid crystal display device including a liquid crystal panel that displays video and a light source that illuminates the liquid crystal panel. There has been disclosed a liquid crystal display device capable of realizing appropriate screen display luminance according to video content and sufficiently reducing power consumption by changing the light emission luminance characteristics of the light source. In this liquid crystal display device, the increase or decrease in the light emission luminance of the light source is adjusted while maintaining the white chromaticity (white balance) substantially constant.

Japanese Patent Laid-Open No. 9-80378 JP 2007-47733 A

  Thus, conventionally, as an enhancement function that emphasizes the light emitting part of the video signal, the maximum and minimum values of the pixel value of the video signal are viewed, the gradation of the high part is stretched and lifted, or the low part Processing to compress and drop the gradation is performed.

  However, since the standardized video signal does not actually express the brightness that appears bright to the human eye, it is difficult to specify the light emitting part only from the gradation value as in the conventional enhancement function. In other words, even if enhancement is performed by uniformly looking at the maximum value and the minimum value of various image values, a high-contrast and high-quality image is not always obtained.

  When enhancing display brightness in variously changing images, a relatively brightly shining portion (light emitting portion) is detected from the luminance distribution of the image, and the luminance of the light source is stretched and increased to remove non-emitting portions. If the display brightness of the light-emitting part is consciously enhanced by reducing the brightness of the video signal in the light-emitting part, the human eye will see a contrast and an increase in brightness. Although it is possible to provide a high-quality display image with improved image quality by making the light emission part more conspicuous, conventionally, enhancement processing based on such a concept has not been performed.

  Then, when performing the enhancement process in which the light emission part is more conspicuous on such a screen, it may be uncomfortable if it is excessively performed. Therefore, it is desirable to change the degree of the enhancement process depending on the genre of the video.

  Note that the enhancement function described in Patent Document 1 is for adjusting the contrast for the purpose of compensating for the change in brightness caused by the brightness adjustment of the backlight device, and is not intended to consciously enhance the light emitting part of the image. Absent.

  In addition, the liquid crystal display device described in Patent Document 2 switches light emission luminance control of a backlight light source in conjunction with a genre in order to achieve the purpose of power saving, and does not have an enhancement function. Therefore, in the technique described in Patent Document 2, there is no idea of consciously enhancing the light emitting part of the video.

  The present invention has been made in view of the above circumstances, and detects a light emitting portion of a video from a video signal, stretches and increases the luminance of a light source, and removes a non-light emitting portion excluding a light emitting portion. An object of the present invention is to enhance the display brightness of a light emitting part by reducing the brightness of a video signal so as to make the display stand out and to display an image with an increased contrast and a high contrast.

  In order to solve the above-described problem, the first technical means includes a display unit that displays an input video signal, a light source that illuminates the display unit, a control unit that controls the display unit and the light source, and the input A genre information detection unit that detects genre information of a video signal, wherein the control unit is based on an index related to brightness calculated based on a predetermined condition from the input video signal, Stretching and increasing the luminance of the light source, and further generating a histogram in which the number of pixels is integrated with respect to a predetermined feature amount related to the brightness of the input video signal, and an upper region of the predetermined range of the histogram By detecting the light emitting part and reducing the luminance of the video signal of the non-light emitting part excluding the light emitting part, the display luminance of the light emitting part is enhanced, and according to the genre information, It is obtained characterized by switching the control curve whose serial and indicator associated to the brightness determining the relationship between the luminance stretch quantity for stretching the luminance of the light source.

  According to a second technical means, in the first technical means, the control unit divides the image based on the input video signal into a plurality of regions, and based on the gradation value of the video signal in the divided region which is the divided region. The lighting rate of the light source region corresponding to each of the divided regions is changed, and the control curve includes an average lighting rate obtained by averaging the lighting rates of the light source regions for all the light source regions, and the average lighting rate. A control curve that defines a relationship with a luminance stretch amount indicated by a maximum display luminance that can be taken on a screen of the display unit that is related in advance to a rate, wherein the control unit uses the brightness as an index related to the brightness The average lighting rate is used, and the luminance of the light source is stretched based on the luminance stretch amount determined according to the average lighting rate.

  According to a third technical means, in the first technical means, the control curve counts the number of pixels by weighting the brightness of each pixel with respect to an image in a predetermined range including the detected light emitting portion region. Is a control curve that defines a relationship between a score indicating the degree of brightness calculated by the above and the luminance stretch amount, wherein the control unit uses the score as an index related to the brightness and calculates from the input signal The brightness of the light source is stretched based on the brightness stretch amount corresponding to the score.

  According to a fourth technical means, in the second or third technical means, the control unit performs video processing for converting and outputting an input gradation of an input video signal, and determines a relationship between the input gradation and the output gradation. The input / output characteristic to be determined has a threshold value determined in a region of a non-light-emitting portion having a lower gradation than a boundary between the light-emitting portion and the non-light-emitting portion, and the control unit is configured to input a video signal according to the luminance stretch amount. A gain at which an output gradation is lowered with respect to an input gradation is determined in advance, and the image processing is performed by applying the determined gain to a region having a gradation lower than the threshold value. The threshold value is changed based on information.

  A fifth technical means is the technical means according to any one of the first to fourth aspects, wherein the control unit is equal to or greater than thresh = A + Nσ (N is a constant), where A is the average value of the histogram and σ is the standard deviation. This pixel is a light emitting part.

  A sixth technical means is the technical means according to any one of the first to fifth aspects, wherein the control unit calculates an increase in display luminance of the display unit due to a luminance stretch of the light source in the non-light-emitting part. It is characterized in that it is reduced by lowering the luminance of the input video signal.

  The seventh technical means is a television receiver provided with a video display device which is any one of the first to sixth technical means.

  According to the video display device of the present invention, the light emitting portion of the video is detected from the video signal, the luminance of the light source is stretched and increased, and the luminance of the video signal of the non-light emitting portion excluding the light emitting portion is reduced. Thus, it is possible to enhance and enhance the display luminance of the light emitting portion to display an image with increased brightness and increased contrast. Furthermore, according to the video display device of the present invention, the genre information of the video is detected, and the luminance stretch amount of the light source and the gain of the video signal of the non-light emitting part are changed according to the genre information. It is possible to display an image with no sense of incongruity with adjusted brightness and contrast.

It is a figure for demonstrating one Embodiment of the video display apparatus based on this invention, and shows the structural example of the principal part of a video display apparatus. It is a figure which shows the control curve for demonstrating the process example of the area active control and brightness | luminance stretch part of the video display apparatus of FIG. 1 in case a genre information is a standard program. It is a figure for demonstrating the calculation process example of the average lighting rate in the area active control and luminance stretch part of the video display apparatus of FIG. It is a figure for demonstrating the average lighting rate of the backlight of FIG. 3, and the gradation value of a pixel. It is a figure for demonstrating the relationship between Y histogram produced | generated from the luminance signal Y of the input video signal, and a light emission part. It is a figure which shows an example of the tone mapping which the mapping part of the video display apparatus of FIG. 1 produces | generates when a genre information is a standard program. It is a figure which shows the control curve for demonstrating the Max brightness | luminance output in the area active control and brightness | luminance stretch part of the video display apparatus of FIG. It is a figure which shows the state in which screen brightness | luminance is enhanced by the process of the area active control and brightness | luminance stretch part of the video display apparatus of FIG. It is a figure which shows the control curve for demonstrating the process example of the area active control and brightness | luminance stretch part of the video display apparatus of FIG. 1 when genre information is variety. It is a figure which shows an example of the tone mapping which the mapping part of the video display apparatus of FIG. 1 produces | generates when genre information is variety. It is a figure which shows the control curve for demonstrating the process example of the area active control and brightness | luminance stretch part of the video display apparatus of FIG. 1 in case a genre information is a movie. It is a figure which shows an example of the tone mapping which the mapping part of the video display apparatus of FIG. 1 produces | generates when genre information is a movie. It is a figure which shows the control curve for demonstrating the process example of the area active control and brightness | luminance stretch part of the video display apparatus of FIG. 1 in case genre information is news animation. It is a figure which shows an example of the tone mapping which the mapping part of the video display apparatus of FIG. 1 produces | generates when genre information is news animation. It is a figure for demonstrating other embodiment of the video display apparatus which concerns on this invention, and shows the other structural example of the principal part of a video display apparatus. An example of a histogram generated from a luminance signal of an input video signal is shown. It is a figure which shows the control curve of the luminance stretch amount according to the score of the pixel more than a 3rd threshold value in the case where a genre information is a standard program. It is a figure which shows the control curve of the luminance stretch amount according to the score of the pixel more than a 3rd threshold value when a genre information is variety. It is a figure which shows the control curve of the luminance stretch amount according to the score of the pixel more than the 3rd threshold value when genre information is a movie. It is a figure which shows the control curve of the luminance stretch amount according to the score of the pixel more than the 3rd threshold value when genre information is news animation. It is a figure for demonstrating other embodiment of the video display apparatus which concerns on this invention, and shows the further another structural example of the principal part of a video display apparatus. It is a figure explaining the method of calculating CMI from the broadcast video signal which should be displayed with a video display apparatus. It is a figure explaining the brightest color in the pixel which has RGB data.

(Embodiment 1)
FIG. 1 is a diagram for explaining an embodiment of a video display device according to the present invention, and shows a configuration example of a main part of the video display device. The video display device has a configuration in which an input video signal is subjected to image processing to display a video, and can be applied to a television receiver or the like.

  1 includes a signal processing unit 1, a genre information detection unit 4, an area active control / luminance stretch unit 5, a backlight control unit 6, a backlight unit 7, a display control unit 8, and an input video signal. Is provided. Here, the signal processing unit 1 includes a light emission detection unit 2 and a mapping unit 3. As an example of the control unit of the present invention, the backlight unit 7 and the display unit 9 are controlled. The signal processing unit 1, the area active control / luminance stretch unit 5, the backlight control unit 6, and the display The control part 8 corresponds.

  The video signal separated from the broadcast signal and the video signal input from the external device are input to the signal processing unit 1 and the area active control / luminance stretch unit 5. At this time, the video signal to the area active control / luminance stretch unit 5 is input to the area active control / luminance stretch unit 5 after applying the tone mapping generated by the mapping unit 3 of the signal processing unit 1.

  The genre information detection unit 4 obtains genre information related to the video signal based on the metadata superimposed on the broadcast signal. Specifically, the genre information detection unit 4 extracts SI (Service Information) including program information from the broadcast stream, and acquires genre information for each broadcast program therefrom. Further, the genre information of the broadcast program to be reproduced may be obtained from a server device on the Internet. The broadcast program genre includes news / report, sports, information / wide show, drama, music, variety, movie, animation / special effects, documentary / cultural, theater / performance, hobby / education, welfare, and the like.

  The area active control / luminance stretch unit 5 divides the image based on the video signal into predetermined areas in accordance with the input video signal, and extracts the maximum gradation value of the video signal for each divided area. Based on the extracted value, the lighting rate of the backlight unit 7 is calculated. The lighting rate is determined for each area of the backlight unit 7 corresponding to the divided area of the video, and the lighting rate here is actually changed by a stretch process as will be described later. It can be said that there is.

  Moreover, the backlight part 7 is an example of the light source for illuminating the display part 9, is comprised by several LED, and brightness | luminance control is possible for every area | region. The lighting rate for each region of the backlight unit 7 is determined based on a predetermined arithmetic expression, but is basically maintained without decreasing the luminance of the LED in a region having a bright maximum gradation value of high gradation. Then, an operation for reducing the luminance of the LED in a region having a dark maximum gradation value with low gradation is performed. Note that the lighting rate may be calculated from other feature quantities related to the brightness of the input video signal, such as an average gradation value instead of the maximum gradation value, and when calculating from the average gradation value, Instead of a region having a dark maximum gradation value, a region having a bright average gradation value and a dark region may be applied.

Then, the area active control / luminance stretch unit 5 calculates the overall average lighting rate of the backlight unit 7 from the lighting rate of each region, and according to the average lighting rate, the backlight unit 7 is calculated by a predetermined arithmetic expression. The maximum light emission luminance stretch amount (hereinafter referred to as “luminance stretch amount”) is calculated. The average lighting rate is an example of an index related to brightness in the present invention. By stretching the maximum light emission luminance of the backlight unit 7 (the maximum light emission luminance of the LED) by this luminance stretch amount, the maximum screen luminance that can be taken in all areas in the screen can be stretched by a predetermined amount from the reference luminance. it can. The reference luminance from which the stretching is performed is such a luminance that the screen luminance is 550 (cd / m ² ) at the maximum gradation value, for example. The reference luminance can be appropriately determined without being limited to this example.

Hereinafter, the maximum screen luminance after stretching at the maximum gradation value that can be taken in the entire area in the screen is referred to as “Max luminance”. As described above, since the luminance stretch amount is a value determined by the average lighting rate, and the Max luminance is a value determined by the luminance stretch amount, the Max luminance depends on the average lighting rate as illustrated in the control curve of FIG. It can be said that the value is determined. FIG. 2 is a diagram for explaining a processing example in the area active control / luminance stretch unit 5 in the case where the genre information is a standard program, with respect to the average lighting rate (window size) of the backlight unit 7. An example of a control curve showing the relationship of Max luminance (cd / m ² ) is shown, and is a control curve when the input video signal is a standard program.

In the control curve of FIG. 2, the Max luminance is smaller than the reference luminance (550 cd / m ^{2 in} this example) in a range where the average lighting rate is small, and the luminance stretch amount is negative. Yes. Even if there is a scene where the luminance stretch amount is negative depending on the average lighting rate as in this example, the integrated value obtained by integrating the Max luminance control curve of FIG. 2 over all the average lighting rates is the reference luminance. Therefore, it can be said that the maximum light emission luminance and the maximum screen luminance (that is, the maximum display luminance) are enhanced by “stretching” as a whole.

  The area active control / luminance stretch unit 5 changes the above-described lighting rate (temporary lighting rate) for each region so that the maximum light emission luminance is stretched by the luminance stretch amount calculated according to the average lighting rate. Such control of the lighting rate for each divided region including calculation of the lighting rate for each divided region and change of the lighting rate in accordance with the average lighting rate (calculation of the lighting rate after stretching) is referred to as area active control. . In this way, the image by the input video signal is divided into a plurality of areas, and the lighting rate of the area of the light source corresponding to the divided area is changed based on the gradation value of the video signal of the divided area, An average lighting rate obtained by averaging the lighting rates of the light source regions is calculated for each of the regions, and based on the maximum display luminance (Max luminance) that can be taken on the screen of the display unit 9 associated in advance with the average lighting rate. It is preferable to stretch the luminance.

  Further, the area active control / luminance stretch unit 5 outputs Max luminance determined according to the average lighting rate to the mapping unit 3 of the signal processing unit 1 for feedback.

  The light emission detection unit 2 of the signal processing unit 1 generates a histogram for each frame based on a predetermined feature amount related to the brightness of the input video signal, and detects a light emitting part. The light emitting portion is obtained from the average value and standard deviation of the histogram, and is detected as a relative value for each histogram. As described above, the light emission detection unit 2 generates a histogram in which the number of pixels is integrated with respect to a predetermined feature amount related to the brightness of the input video signal, and detects an upper region of the predetermined range of the histogram as a light emission portion. To do.

The N + 1-th frame f _{N + 1} of the input video signal will be described. The mapping unit 3 includes information on the light emission part detected for the frame f _{N + 1} by the light emission detection unit 2 and _N output from the area active control / luminance stretch unit 5. The tone intensity for frame f _{N + 1} is generated using the Max luminance of the f th frame f _N and output to the multiplier for application to frame f _{N + 1} of the input video signal. This tone mapping is generated so as to reduce the luminance corresponding to the luminance stretch of the backlight unit 7 with respect to the portion (non-light emitting portion) regarded as not emitting light in the frame fN _{+ 1} . The multiplier is used to apply the tone mapping to the input video signal, for each pixel value of the frame f _{N + 1} of the video signal, by multiplying the gain coefficient indicated by the tone mapping for the frame f _{N + 1,} Area Output to the active control / luminance stretch unit 5.

Further, the area active control / luminance stretch unit 5 outputs control data for controlling the backlight unit 7 to the backlight control unit 6, and the backlight control unit 6 determines the backlight unit 7 based on the data. The light emission luminance of the LED is controlled for each divided area. This control data is data for controlling the backlight unit 7 so that the lighting rate after stretching for each region described above is obtained. Control data to the backlight unit 7 of rendering the frame f _{N + 1} of the input video signal, for a frame f _{N + 1} of the video signal to which the tone mapping obtained by feeding back the Max luminance of the frame f _N, the backlight unit After calculating the lighting rate for each of the seven areas based on the above-described predetermined arithmetic expression, it can be obtained by changing by stretching. Although the brightness | luminance of LED of the backlight part 7 is performed by PWM (Pulse Width Modulation) control, it can also be controlled to become a desired value by electric current control or these combination.

Further, the area active control / luminance stretch unit 5 outputs display control data for controlling the display unit 9 to the display control unit 8, and the display control unit 8 displays the display on the display unit 9 based on the display control data. To control. Display control data when displaying the frame f _{N + 1} of the input video signal, the video signal after the application of the tone mapping obtained by feeding back the Max luminance of the frame f _N to the frame f _{N + 1,} video indicated by the video signal Is data for controlling the display unit 9 to display. The display unit 9 is a liquid crystal panel that is illuminated by the LED of the backlight unit 7 and displays an image.

  As described above, in the area active control / luminance stretch unit 5 according to the first embodiment, the backlight luminance is stretched according to the average lighting rate to increase the luminance of the LED of the backlight unit 7, and information on the luminance stretch (above described) Is returned to the signal processing unit 1, and the luminance corresponding to the luminance stretch of the backlight unit 7 is reduced with respect to the video signal. Then, the luminance stretch is applied to the entire backlight unit 7, and the luminance reduction due to the video signal processing is performed on a portion (non-light emitting portion) that is regarded as not emitting light except the light emitting portion.

  That is, in the area active control / luminance stretch unit 5, the backlight luminance is stretched to increase the luminance of the LED of the backlight unit 7, and the luminance of the video signal of the non-light emitting portion of the input video signal is decreased. This enhances the display luminance of the light emitting portion (hereinafter referred to as “light emitting partial enhancement processing”). By such video signal processing and backlight luminance control processing, it is possible to increase the screen luminance of only the light emitting part, to perform video expression with high contrast, and to improve image quality.

  As processing for reducing the luminance of the video signal of the non-light-emitting portion of the input video signal, reducing the luminance corresponding to the luminance stretch of the backlight unit 7 with respect to the non-light-emitting portion is the screen luminance of the non-light-emitting portion. Is preferable in order to maintain a certain level. In other words, the area active control / luminance stretch unit 5 calculates the increase in display luminance of the display unit 9 due to the luminance stretch of the light source in the non-light-emitting portion (that is, the predetermined region where the predetermined feature amount is low). It is preferable to reduce the brightness.

  The main object of the present invention is to adjust the brightness and contrast according to the genre of the image while performing the light emission partial enhancement process on the input video signal to enhance the brightness and contrast. As a configuration for this, the video display device includes a genre information detection unit 4 that detects genre information of an input video signal, a signal processing unit 1 that is an example of a control unit of the present invention, and an area active control / luminance stretch unit 5. Is provided. Then, according to the genre information of the input video signal, the control curve that determines the relationship between the index relating to the brightness and the stretch amount for stretching the luminance of the light source is switched. As a result, it is possible to prevent the enhancement process that emphasizes the light emission portion on the screen from being excessively performed, and to display a video with no sense of incongruity.

  When the video display device as described above is configured as a television receiving device, the television receiving device has means for selecting and demodulating a broadcast signal received by an antenna, decoding and generating a reproduction video signal, The reproduction video signal is appropriately subjected to predetermined image processing and input as the input video signal in FIG. Thereby, the received broadcast signal can be displayed on the display unit 9. The present invention can be configured as a video display device and a television receiver including the video display device.

Hereinafter, a processing example of each unit of the present embodiment having the above-described configuration will be described more specifically.
FIG. 3 is a diagram for explaining a calculation process example of the average lighting rate in the area active control / luminance stretch unit 5, and FIG. 4 explains the average lighting rate of the backlight and the gradation value of the pixel in FIG. It is a figure for doing.

  Area active control applied to the embodiment of the present invention divides an image into a plurality of predetermined regions (areas), and controls the light emission luminance of the LEDs corresponding to the divided regions for each region. Here, the area active control / luminance stretch unit 5 divides the image of one frame into a plurality of predetermined areas (the above-mentioned areas) based on the input video signal, and the LEDs corresponding to the divided areas. The light emission luminance is controlled for each divided region.

  First, the area active control / luminance stretch unit 5 divides the video image exemplified in FIG. 3A into 12 parts in the vertical direction as shown in FIG. Are divided into 144 areas. In addition, it is assumed that at least one LED is disposed for each region as the backlight unit 7.

  Then, the area active control / luminance stretch unit 5 extracts the maximum gradation value of the video signal for each region, and determines the provisional lighting rate of the LED for each region according to the extracted maximum gradation value. As described above, other brightness-related feature quantities such as the average gradation value of the video signal may be used instead of the maximum gradation value. A statistical value is used as this feature quantity. Hereinafter, an example in which the maximum gradation value is extracted will be described. In FIG. 3B, the LED lighting rate is shown in gray scale for each region. For example, in the image of FIG. ) To increase the lighting rate and make it brighter. The process at this time will be described more specifically.

  FIG. 3C shows an example of the state when the maximum gradation value is extracted from each divided area of one frame and the lighting rate corresponding to the maximum gradation value. FIG. 3D shows the lighting rate of each area and the average lighting rate of the entire screen. 3 (C) and 3 (D), an example in which a screen of one frame is divided into eight areas (area Nos. 1 to 8) is given for simplicity of explanation, but as shown in FIG. 3 (B). Processing can be performed by dividing into many regions, and processing can be performed by dividing the region into the same number of regions as the number of LEDs provided in the backlight unit 7 at the maximum.

  First, area no. For each of the areas 1 to 8, the lighting rate of the temporary LED of the backlight in the area is calculated from the maximum gradation value in the area. The provisional lighting rate can be indicated by, for example, an LED driving duty (hereinafter referred to as “LED duty”). In this case, the maximum value of the lighting rate is 100%. As described above, the brightness of the LED is controlled to be a desired value by PWM and / or current control. In the following description, an example in which only PWM control is employed for the sake of simplification of description. Cite. However, although not particularly touched, when the final LED duty exceeds 100% due to the luminance stretch, the predetermined luminance may be obtained by increasing the current value by using current control together.

  In determining the provisional lighting rate of the LED in each region, the luminance of the backlight is lowered by lowering the lighting rate in a dark region where the maximum gradation value is low. The actual lighting rate of each area is determined so that the gradation to be displayed is accurately displayed and the LED duty is made as low as possible. The LED duty in each area is desired to be as low as possible, but it is necessary to display accurately without squashing the gradation to be displayed. Therefore, an LED that can display the maximum gradation in the area and lowers the LED duty as much as possible. The duty (temporary lighting rate) is set, and the gradation of the display unit 9 (LCD panel here) is set based on the duty.

As an example, when the gradation value of the video is expressed by 8-bit data of 0 to 255, the gradation values of a plurality of pixels in one area in FIG. ) Will be described. In the pixel group shown in FIG. 4A, the maximum gradation value is 128. In this case, as shown in FIG. 4B, the backlight lighting rate in the area is (1 / (255). / 128)) ^2.2 = 0.217 times (21.7%). Then, the area active control / luminance stretch unit 5 determines the provisional lighting rate in this way and considers the gradation value for each pixel in the display unit 9 in consideration of the provisional lighting rate for the region including the pixel. To calculate. For example, when the gradation value to be displayed is 96, since 96 / (128/255) = 192, the pixel may be expressed using the gradation value 192. Similarly, FIG. 4C shows the result of calculating the gradation value for display for each pixel in FIG.

  In the present invention, since the luminance stretch is performed based on the average lighting rate obtained from the provisional lighting rate, the actual lighting rate is not 21.7% in the above-described case. The luminance stretch in the previous frame) is already reflected by the tone mapping by the mapping unit 3, and the result is the gradation value to be displayed (illustrated by “96”). Therefore, the display control unit 8 may perform display control of the display unit 9 with the display control data of the gradation values shown in FIG. 4C for the pixel group shown in FIG.

  In the example of FIG. 3C, the lighting rate of the backlight is determined in the range of 10 to 90% as indicated by the percentage with respect to the maximum gradation value of each area indicated by the gray scale. FIG. 3D is a graph in which the percentages in FIG. 3C are arranged for each area. This lighting rate calculation method shows an example. Basically, a bright high gradation region does not decrease the backlight luminance, and the backlight luminance is decreased in advance in a low gradation dark region. The provisional lighting rate of each area is calculated according to the determined arithmetic expression.

  Next, the area active control / luminance stretch unit 5 averages the temporary lighting rate of the backlight for each region calculated from the maximum gradation value of the video signal, and calculates the average lighting rate of the backlight unit 7 in one frame. calculate. The calculated average lighting rate of the entire screen naturally increases as the number of regions having a high lighting rate increases in each region. In this example, the average lighting rate becomes a level as shown by a solid line in FIG. 3D, and the actual value is about 53%.

  The actual luminance of the backlight unit 7 is determined based on the maximum emission luminance value (maximum emission luminance corresponding to the Max luminance described above) determined according to the average lighting rate, that is, based on the luminance stretch amount. This is enhanced by stretching the provisional lighting rate of each area.

  This Max luminance is the maximum screen luminance that can be taken, and is determined based on the relationship shown in FIG. 2, for example. The horizontal axis in the control curve of FIG. 2 is the average lighting rate (window size) of the backlight, and this average lighting rate is calculated based on a lighting region (window region) with a lighting rate of 100% and a non-lighting region with a lighting rate of 0%. It can be expressed as a ratio of The average lighting rate is zero when there is no lighting region, the average lighting rate increases as the window of the lighting region increases, and the average lighting rate becomes 100% for all lighting.

In FIG. 2, the Max luminance when the backlight is fully lit (average lighting rate 100%) is, for example, 550 (cd / m ² ), and this is the reference luminance before stretching. In the present embodiment, the Max luminance is increased as the average lighting rate decreases from 100%. In the case of 8-bit representation, a pixel having a gradation value of 255 gradations has the highest screen brightness in the screen, and the maximum possible screen brightness (Max brightness). From this, it can be seen that even with the same average lighting rate, the screen luminance does not increase up to the Max luminance depending on the gradation value of the pixel.

FIG. 2 shows a control curve in the case where the input video signal is a standard program (hereinafter referred to as “standard mode”). When the average lighting rate is P, the value of Max luminance is the largest, The maximum screen brightness at this time is 1500 (cd / m ² ). In other words, at P, the maximum possible screen brightness is stretched to 1500 (cd / m ² ) compared to 550 (cd / m ² ) when all the lights are on. P is set at a position where the average lighting rate is relatively low. In other words, the brightness of the backlight is stretched to a maximum of 1500 (cd / m ² ) when the screen is a dark screen as a whole with a low average lighting rate and a high gradation peak in part. Therefore, FIG. 2 is an example of a control curve that defines the relationship between the index relating to brightness and the stretch amount for stretching the luminance of the light source in the present invention.

  Also, the reason for the lower stretch of backlight brightness is the higher the average lighting rate, the less bright the screen is because it may feel dazzling if the backlight brightness is excessively high on an originally bright screen. It is for doing so.

  In addition, the range with a low average lighting rate corresponds to a dark screen image, and rather than increasing the screen brightness by stretching the backlight brightness, the backlight brightness is reduced to improve the contrast, It is preferable to maintain the display quality by suppressing black float. Therefore, in the example of FIG. 2, such a setting for suppressing black floating at the low average lighting rate is adopted, and the value of Max luminance is gradually decreased from the average lighting rate P to the average lighting rate 0 (all black). I am letting.

  The area active control / luminance stretch unit 5 stretches the luminance of the backlight according to the control curve in FIG. 2 and outputs the control signal to the backlight control unit 6. Here, as described above, the average lighting rate changes according to the maximum gradation value detected for each divided region of the video, and the state of the luminance stretch changes according to the average lighting rate.

  The video signal input to the area active control / luminance stretch unit 5 is applied with tone mapping generated by signal processing by the signal processing unit 1 described below, and the low gradation region is gain-down. As a result, the luminance of the backlight is stretched in the low-tone non-light-emitting area, and the luminance is reduced by reducing the gain of the video signal.As a result, the screen brightness is enhanced only in the light-emitting area, resulting in a sense of brightness. It has come to increase.

  The area active control / luminance stretch unit 5 outputs the Max luminance value obtained from the average lighting rate of the backlight according to the control curve of FIG. 2 to the mapping unit 3 of the signal processing unit 1. The mapping unit 3 performs tone mapping using the Max luminance output from the area active control / luminance stretch unit 5.

Next, the signal processing unit 1 will be described.
The light emission detection unit 2 of the signal processing unit 1 detects a light emitting part from the video signal. FIG. 5 is a diagram illustrating an example of a Y histogram generated from the luminance signal Y of the input video signal. The light emission detection unit 2 adds up the number of pixels for each luminance gradation for each frame of the input video signal to generate a Y histogram. The horizontal axis represents the gradation value of luminance Y, and the vertical axis represents the number of pixels (frequency) integrated for each gradation value. Here, it is assumed that a light emitting portion is detected for luminance Y. The luminance Y is an example of a feature amount of an image for creating a histogram for detecting a light emitting portion, and another example of the feature amount will be described later.

When the Y histogram is generated, an average value (Ave) and a standard deviation (σ) are calculated from the Y histogram, and two threshold values Th are calculated using these.
The second threshold value Th2 defines a light emission boundary, and processing is performed on the assumption that pixels above the threshold value Th2 in the Y histogram are light emitting portions. The second threshold Th2 can be expressed by the following equation (1), where N is a predetermined constant and σ is a standard deviation. That is, the light emission detection unit 2 detects pixels equal to or greater than Th2 in the following expression (1) as light emission portions.
Th2 = Ave + Nσ Expression (1)

The first threshold value Th1 is set to suppress a sense of incongruity such as gradation in a region smaller than Th2, and is expressed by the following expression (2), where M is a predetermined constant that satisfies M <N. Can do.
Th1 = Ave + Mσ Expression (2)
The values of the first and second threshold values Th1 and Th2 detected by the light emission detection unit 2 are output to the mapping unit 3 and used to generate tone mapping.

  FIG. 6 is a diagram illustrating an example of tone mapping generated by the mapping unit 3. In FIG. 6, the horizontal axis is the input gradation of the luminance value of the video, and the vertical axis is the output gradation. The pixels with the second threshold Th2 or more detected by the light emission detection unit 2 are light emitting portions in the image, and the gain is reduced by applying a compression gain except for the light emitting portions. At this time, if the output gradation is suppressed by uniformly applying a constant compression gain to a region smaller than Th2, which is the light emission boundary, a sense of incongruity occurs in the gradation. Accordingly, the light emission detector 2 sets the first threshold Th1, applies the first gain G1 to the region smaller than Th1, and the second gain G2 so as to linearly connect Th1 and Th2. Set tone mapping.

A method for setting the gain will be described.
The mapping unit 3 receives the Max luminance value from the area active control / luminance stretch unit 5. As described above, the Max luminance indicates the maximum screen luminance determined from the average lighting rate of the backlight. For example, the value of the backlight duty (LED duty) indicating the maximum light emission luminance can be input. it can.

The first gain G1 is applied to a region smaller than the first threshold Th1, and is set by the following expression (3).
G1 = (Ls / Lm) ^{1 / γ} Expression (3)
Here, Ls is the reference luminance (reference luminance when the backlight luminance is not stretched; for example, the luminance when the maximum screen luminance is 550 cd / m ² ), and Lm is the area active control / luminance stretching unit. 5 is the Max luminance output from 5. Therefore, the first gain G1 applied to the region smaller than the first threshold Th1 lowers the output gradation of the video signal so as to reduce the screen luminance that increases due to the luminance stretch of the backlight.

For tone mapping of the second threshold Th2 or more, f (x) = x. That is, input gradation = output gradation, and processing for lowering the output gradation is not performed. Between the first threshold Th1 and the second threshold Th2, the output gradation of the first threshold Th1 lowered by the first gain G1 and the output gradation of the first threshold Th1 are connected by a straight line. Set as follows. That is, the second gain G2 is determined by G2 = (Th2-G1 · Th1) / (Th2-Th1).
Through the above processing, tone mapping as shown in FIG. 6 is obtained. At this time, with respect to the connecting portions of Th1 and Th2, a predetermined range (for example, connecting portion ± Δ (Δ is a predetermined value)) may be smoothed by a quadratic function.

  The tone mapping generated by the mapping unit 3 is applied to the input video signal, and the video signal in which the output of the low gradation part is suppressed based on the luminance stretch amount of the backlight is input to the area active control / luminance stretch unit 5.

FIG. 7 is a diagram for explaining the Max luminance of the frames f _N and f _{N + 1} output from the area active control / luminance stretch unit 5. The control curve shown in FIG. 7 is the same as the control curve shown in FIG.

As described above, the area active control / luminance stretch unit 5 inputs the video signal to which the tone mapping generated by the mapping unit 3 is applied, performs area active control based on the video signal, and Max based on the average lighting rate. The brightness is also determined. The frame of this time is the frame f _N. The value of Max luminance frame _{f N} is output to the mapping portion 3. The mapping unit 3, using the Max luminance of the frame f _N input to produce a tone mapping as shown in FIG. 6, is applied to the frame f _{N + 1} of the video signal.

Thus, in this embodiment, Max luminance based on the average lighting rate of area active control is fed back and used for tone mapping of the next frame. Mapping unit 3, based on the Max luminance determined by the frame f _N, as described in FIG. 6, applying a gain (first gain G1) to reduce the video output for the first threshold value Th1 smaller area To do. The second gain G2 that linearly connects Th1 and Th2 is applied to the region between Th1 and Th2, and the video output between Th1 and Th2 is reduced.

In the example of FIG. 7, the average lighting rate is not less than the high lighting rate region P, the gain to reduce the video output of the non-light emitting portion in the frame f _N is applied, the frame f _{N + 1,} the maximum per area The gradation value tends to decrease and the lighting rate tends to decrease. As a result, Max luminance tends to increase in the frame f _{N + 1} . As a result, in the frame fN _{+ 1} , the luminance stretch amount of the backlight is further increased, and the brightness of the screen tends to increase. However, this tendency is not seen in the region where the lighting rate is lower than P, and the reverse tendency occurs.

FIG. 8 is a diagram illustrating a state in which the screen luminance is enhanced by the processing of the area active control / luminance stretch unit 5. In FIG. 8, the horizontal axis is the gradation value of the input video signal, the vertical axis is the screen luminance (cd / m ² ) of the display unit 9, and S2 and S3 are the first and second used in the light emission detection unit 2, respectively. This corresponds to the position of the gradation values of the second threshold values Th1 and Th2.

As described above, in the region equal to or greater than the second threshold Th2 detected by the light emission detection unit 2, signal processing for reducing the output gradation of the video signal according to the luminance stretch amount of the backlight is not performed. As a result, in S3 to S4, the input video signal is enhanced and displayed with a γ curve according to the Max luminance determined by the area active control. S4 indicates the screen luminance when the input video signal has the maximum gradation value (255). For example, when the Max luminance is 1500 (cd / m ² ), the screen luminance at the maximum gradation is 1500 (cd). / M ² ).

  On the other hand, in the case of input gradation values from S1 to S2, as described above, the first gain G1 is applied to the video signal so as to reduce the screen luminance component that increases due to the luminance stretch of the backlight. Therefore, the screen is displayed with a γ curve based on the reference luminance. This is because the output value of the video signal is suppressed in a range smaller than the threshold Th1 (corresponding to S2) corresponding to the luminance stretch by the mapping unit 3 in accordance with the Max luminance determined by the area active control / luminance stretch unit 5. In S2 to S3, the screen brightness changes according to the tone mapping of Th1 to Th2.

When the Max luminance increases, the difference in the screen luminance direction between the curve based on the reference luminance of S1 to S2 and the curve based on the Max luminance of S3 to S4 increases. As described above, the curve based on the reference brightness indicates that the maximum brightness value screen brightness is the reference brightness when the backlight brightness is not stretched (for example, the maximum brightness value screen brightness is 550 cd / m ² ). The curve based on the Max luminance is a γ curve in which the screen luminance of the maximum gradation value becomes the Max luminance determined by the area active control / luminance stretch unit 5.

  Thus, the control unit controls the screen brightness with the reference brightness when the input video signal is between the 0th gradation (S1) and S2. This is because, in the case of dark images with low gradation, if the brightness is increased and displayed, deterioration of the product such as lowering of contrast or black float will occur. This is to prevent the screen brightness from increasing.

  In addition, since the range where the input video signal is greater than or equal to S3 is a range that is considered to emit light, the video signal is maintained without being suppressed while the backlight is stretched by luminance stretching. Thereby, the screen brightness is enhanced, and a high-quality image display with a more lustrous feeling can be performed. The γ curves from S1 to S2 do not need to match the reference luminance, and can be set by appropriately adjusting the gain G1 as long as it has a level different from the enhancement region of the light emitting portion. .

  In the present invention, the light emission partial enhancement processing is changed according to the genre information of the input video signal. Specifically, according to the genre information, the control curve that determines the relationship between the index related to brightness and the stretch amount for stretching the luminance of the light source is switched. Further, an area detected as a light emitting part may be changed or a threshold value of a non-light emitting part that lowers the video signal may be changed according to the genre information.

  As described above, the genre information detection unit 4 detects genre information related to the video signal based on the metadata superimposed on the broadcast signal, and transmits the genre information to the signal processing unit 1 and the area active control / luminance stretch unit 5. ing. The area active control / luminance stretch unit 5 calculates the luminance stretch amount and the Max luminance according to the genre information. A specific example will be described.

  FIGS. 9 to 14 are diagrams for explaining an example of a difference in processing according to genre information in the area active control / luminance stretch unit and the mapping unit, and FIGS. 9 and 10 illustrate cases where the genre information is variety. (Hereinafter referred to as “variety mode”), FIG. 11 and FIG. 12 are when the genre information is a movie (hereinafter referred to as “movie mode”), and FIGS. 13 and 14 are when the genre information is news and animation. It is a figure for demonstrating each example (henceforth "news animation mode").

  FIG. 9 is a diagram showing a control curve showing the relationship of the Max luminance with respect to the average lighting rate. The control curve R1 shows the control curve in the standard mode, and the control curve R2 shows the control curve in the variety mode. Yes. As described above, the light emission partial enhancement process is made different by changing the control curve indicating the relationship of the Max luminance with respect to the average lighting rate due to the difference in the genre information.

As illustrated in FIG. 9, in the variety mode, the maximum luminance at the average lighting rate P is the same as in the standard mode, but the Max luminance value at the average lighting rate P is 1500 (cd / m ^2). For example, 800 (cd / m ² ). Further, the value of Max luminance when the average lighting rate is 100% is the same as in the standard mode. As described above, in the variety mode, the luminance stretch amount in the enhancement process is suppressed. However, in the case of variety, there are many cases where character information such as explanatory text is included in the program, which is excessive. This is because an uncomfortable feeling may occur when the enhancement process is performed. Further, the value of Max luminance is gradually decreased from the average lighting rate P to the average lighting rate 0 (all black), and the backlight is turned off at the average lighting rate 0. This is to prevent dazzling and suppress black floating of the display image at least when the image is entirely dark.

  Next, FIG. 10 is a diagram illustrating an example of tone mapping generated by the mapping unit 3 in the variety mode, where the horizontal axis represents the input gradation of the luminance value of the video, and the vertical axis represents the output gradation. The light emission detection unit 2 transmits the first and second threshold values to the mapping unit 3. In the light emission detection unit 2, in the variety mode, the second threshold value that defines the light emission boundary is changed from the threshold value Th2 in the standard mode to the threshold value Th2 'that is larger than Th2, and the first threshold value is also the threshold value in the standard mode. The value of Th1 is changed to a larger threshold value Th1 ′. Note that the values of the first and second threshold values Th1 and Th2 can be changed by changing the values of M and N in the equations (1) and (2).

  Then, the mapping unit 3 uses the first and second threshold values and the Max luminance from the area active control / luminance stretch unit 5 for pixels equal to or higher than the second threshold value Th2 ′ detected by the light emission detection unit 2. , Input gradation = output gradation, and processing for lowering the output gradation is not performed, and the gain is reduced by applying a compression gain except for the light emitting portion. At this time, similarly to the case of FIG. 6 described above, if the output gradation is suppressed by uniformly applying a constant compression gain to the region smaller than Th2 ′, the lightness detection unit 2 becomes uncomfortable in the gradation. The first threshold Th1 ′ is set and detected at, the first gain G1 ′ is set for the region smaller than Th1 ′, and the second gain is set so as to linearly connect Th1 ′ and Th2 ′. Tone mapping is performed by setting G2 ′. The calculation of the gain is as shown in the above equation (3). In this way, by shifting the second threshold value to the high luminance side, the high luminance region handled as the light emitting portion is reduced, and by shifting the first threshold value to the high luminance side, the gradation in the low luminance region is changed. It can be suppressed over a wider range. For this reason, although the amount of luminance stretch is suppressed, an image with enhanced contrast can be obtained.

Next, the case where the genre information is a movie will be described. FIG. 11 is a diagram showing a control curve showing the relationship of the Max luminance with respect to the average lighting rate. The control curve R1 shows a control curve in the standard mode, and the control curve R3 shows a control curve in the movie mode. In the movie mode, the average lighting rate at which the Max luminance is maximum is shifted to a lower one so that the average lighting rate Q is smaller than the average lighting rate P in the standard mode, and the average lighting rate is The value of the Max luminance at Q is reduced to be 800 (cd / m ² ) instead of 1500 (cd / m ² ), for example. Further, the value of Max luminance when the average lighting rate is 100% is set to, for example, 550 (cd / m ² ) as in the standard mode.

  As described above, in the movie mode, the luminance stretch amount in the enhancement processing is suppressed. This is to prevent excessive glare in the case of a movie and to prevent tiredness even during long-time continuous viewing. Further, the maximum Max luminance is obtained at a relatively low average lighting rate, so that the bright portion in the case of a dark image as a whole is emphasized. Note that the value of the Max luminance is gradually decreased from the average lighting rate Q to the average lighting rate 0 (all black), thereby suppressing black floating of the display image.

  FIG. 12 is a diagram illustrating an example of tone mapping generated by the mapping unit 3 in the movie mode, in which the horizontal axis represents the input gradation of the luminance value of the video, and the vertical axis represents the output gradation. The light emission detection unit 2 transmits the first and second threshold values to the mapping unit 3. In the movie mode, the light emission detection unit 2 changes the second threshold value that defines the light emission boundary from the threshold value Th2 in the standard mode to a threshold value Th2 that is larger than Th2, and also the first threshold value in the standard mode. The value of Th1 is changed to a larger threshold value Th1 ″. Note that the values of the first and second threshold values Th1 and Th2 can be changed by changing the values of M and N in the equations (1) and (2).

  The mapping unit 3 performs tone mapping in accordance with the first and second threshold values and the Max luminance from the area active control / luminance stretch unit 5 in the same manner as described with reference to FIG. Because there is, detailed explanation is omitted. In the movie mode, by shifting the second threshold value to the high luminance side, the high luminance region handled as the light emitting portion is reduced, and the first threshold value is higher than the first threshold value Th1 ′ in the variety mode. By shifting to the side, the gradation in the low luminance region is suppressed in a wider range. For this reason, coupled with the suppression of the luminance stretch amount, it is possible to obtain an image quality with enhanced contrast in an image in a range where the average lighting rate is small.

Next, the case of the news / animation mode will be described. FIG. 13 is a diagram showing a control curve showing the relationship of the Max luminance with respect to the average lighting rate in the news / animation mode, and the control curve R4 shows the control curve in the news / animation mode. In the news / animation mode, the Max luminance with respect to the average lighting rate is always 550 (cd / m ² ), for example. Further, even when the average lighting rate is close to zero (0), the Max luminance value is not lowered. For this reason, the luminance stretch amount is always zero.

  FIG. 14 is a diagram illustrating an example of tone mapping generated by the mapping unit 3 in the news / animation mode, in which the horizontal axis represents the input gradation of the luminance value of the video, and the vertical axis represents the output gradation. The light emission detection unit 2 transmits the first and second threshold values to the mapping unit 3. The light emission detection unit 2 sets the first and second threshold values Th1 and Th2 to zero in the news / animation mode, and f (x) = x for the second Th2 or more, that is, the input floor. Key = Output tone. As a result, in the news / animation mode, the backlight luminance stretch and video signal processing are not performed, and the input video signal is displayed faithfully. In this way, for example, in an animation program, there are many children's viewers, and from the viewpoint of avoiding the influence on visual acuity, the enhancement processing of the light emitting portion is not performed, and image display is performed with emphasis on fidelity. Yes. The same processing is performed for news programs from the viewpoint of image display with an emphasis on fidelity. When displaying the output from the PC, it is desirable to perform the same process of emphasizing fidelity as in the news / animation mode.

(Embodiment 2)
FIG. 15 is a diagram for explaining another embodiment (embodiment 2) of the video display apparatus according to the present invention, and shows another configuration example of the main part of the video display apparatus.

  The second embodiment has the same configuration as that of the first embodiment, but unlike the first embodiment, the Max luminance value used for tone mapping is not determined by the area active control / luminance stretch unit 5. The light emission detection unit 2 determines the luminance stretch amount based on the detection result of the light emission portion and the genre information from the genre information detection unit, and the mapping unit 3 executes tone mapping based on the determined luminance stretch amount. Therefore, unlike the first embodiment, the mapping unit 3 of the signal processing unit 1 does not need to feedback and output the Max luminance value by luminance stretching from the area active control / luminance stretching unit 5.

  FIG. 16 shows an example of a Y histogram generated from the luminance signal Y of the input video signal. As in the first embodiment, the light emission detection unit 2 generates a Y histogram by integrating the number of pixels for each luminance gradation of the pixels for each frame of the input video signal. Then, an average value (Ave) and a standard deviation (σ) are calculated from the Y histogram, and two threshold values Th1 and Th2 are calculated using these values. Similar to the first embodiment, the second threshold value Th2 defines a light emission boundary, and in the Y histogram, pixels that are equal to or higher than the threshold value Th2 are regarded as light emitting portions.

In the present embodiment, in addition to the first threshold Th1 and the second threshold Th2 in the first embodiment, a third threshold Th3 is further set. The third threshold value Th3 is between Th1 and Th2, and is provided for detecting the state of the pixel in the light emitting portion. The threshold value Th3 may be the same value as Th2, but is provided in order to facilitate processing by providing a wider margin for the light emitting portion equal to or greater than Th2. Accordingly, Th3 is expressed by the following equation (4).
Th3 = Ave + Qσ (M <Q ≦ N) (4)

FIG. 17 is a diagram illustrating a luminance stretch control curve according to pixels of the third threshold Th3 or more in the standard mode. The horizontal axis represents the score of the pixel value equal to or greater than the threshold Th3, and the vertical axis represents the luminance stretch amount according to the score.
The score is defined as [ratio of pixels with luminance greater than a certain threshold] × [distance from threshold (luminance difference)], and counts the number of pixels having a gradation value larger than the third threshold Th3, An example of an index related to the degree of brightness, that is, the brightness of the present invention by weighting and calculating the distance from the threshold Th3 is calculated by, for example, the following equation (5).

In equation (5), count [i] is a value obtained by counting the number of pixels for each gradation value i. Further, i ² − (Th3) ² indicates the distance (brightness difference) with respect to the luminance as shown in FIG. 16, and instead, the distance from the threshold value in the lightness L ^* may be adopted. Note that this square represents the luminance and is actually the 2.2th power. That is, when the digital code value is i, the luminance is i ^2.2 . At that time, the lightness L ^* is (i ^2.2 ) ^1/3 ≈ i. As a result of verification with an actual video display device, the difference from the threshold value in luminance was more effective than the difference from the threshold value in brightness. In Equation (5), the total number of pixels is not limited to i> Th3, but is a value obtained by counting all the numbers of pixels. When such a calculated value is adopted as the score, the score increases when there are many high gradation pixels apart from Th3 in the light emitting portion. Even if the number of pixels larger than Th3 is constant, the score is higher as the number of pixels with higher gradation is larger.

Then, as shown by the control curve U1 in FIG. 17, when the score is higher than a certain level, the luminance stretch amount is set high, and the high-grayness shining video is stretched to higher luminance to increase the brightness. In this example, the maximum screen luminance that can be obtained after luminance stretching is set to 1500 (cd / m ² ) in a portion where the score is higher than a certain value (threshold B or higher). When the score is low, the luminance stretch amount is set to be smaller as the score is smaller.

  The luminance stretch amount is the same as that described in the first embodiment, and is indicated by, for example, the value of the backlight duty similarly to the Max luminance. The luminance stretch amount determined according to the values of the first and second threshold values Th1 and Th2 detected by the light emission detection unit 2 and the score of the pixel equal to or greater than Th3 is output to the mapping unit 3 and used for generation of tone mapping. The

The toe mapping process in the mapping unit 3 is the same as in the first embodiment. That is, in the case of the standard mode, as shown in FIG. 6, the first gain G1 is set for a region smaller than Th1 detected by the light emission detector 2, and Th1 and Th2 are linearly connected. A second gain G2 is set. At this time, when setting the gain G1, the luminance stretch amount detected by the light emission detection unit 2 is used, and the luminance is reduced by video signal processing according to the luminance stretch amount of the backlight.
The obtained tone mapping is applied to the input video signal, and the video signal after tone mapping is input to the area active control / luminance stretch unit 5.

  The processing in the area active control / luminance stretch unit 5 is the same as in the first embodiment. However, the area active control / luminance stretch unit 5 does not need to determine the Max luminance from the average lighting rate of the backlight and output it to the signal processing unit 1 as in the first embodiment, and conversely, the signal processing unit 1 emits light. Based on the luminance stretch amount detected by the detection unit 2, the luminance of the LED of the backlight unit 7 is stretched.

  That is, the area active control / luminance stretch unit 5 divides the video into a plurality of predetermined areas (areas), extracts the maximum gradation value of the video signal for each of the divided areas, and according to the extracted maximum gradation value. The LED lighting rate for each area is determined. For example, in a dark region where the maximum gradation value is low, the lighting rate is lowered to lower the backlight luminance. In this state, the input power of the entire backlight is increased in accordance with the amount of luminance stretch to increase the overall luminance of the backlight. As a result, the bright image that is emitted becomes brighter and more radiant. Further, since the luminance corresponding to the luminance stretch is reduced by the video signal processing in the non-light-emitting portion, as a result, the luminance of only the light-emitting portion is increased on the screen, and a high-contrast quality image is displayed be able to. The relationship between the input video signal and the screen luminance is the same as that shown in FIG.

  As described above, the light emission detection unit 2 counts the number of pixels by weighting the brightness of each pixel with respect to an image in a predetermined range (in the above example, a range of Th3 or more) including the detected light emission region. Is used to calculate a score indicating the degree of brightness, determine the luminance stretch amount according to the score and the genre information of the input video signal, and the area active control / luminance stretch unit 5 is stretched by the luminance stretch amount. . Therefore, the luminance stretch amount is output to the area active control / luminance stretch unit 5 and the mapping unit 3. The area active control / luminance stretch unit 5 stretches the luminance according to the luminance stretch amount. The mapping unit 3 reduces the stretched luminance by video signal processing, for example, by changing the gain curve according to the luminance stretch amount.

  Next, a case where the genre information is variety in Embodiment 2 will be described. First, the light emission detection unit 2 changes the control curve of the luminance stretch amount with respect to the score according to the genre information from the genre information detection unit 4. FIG. 18 is a diagram illustrating a control curve of the score and the luminance stretch amount in the variety mode.

In the variety mode, as shown by the control curve U2 in FIG. 18, the luminance stretch amount is constant for the score threshold B or more, but is not 1500 cd / cm ² as in the normal mode, but a smaller value, for example, 800 cd / cm ² , and when the score is smaller than the threshold value B, the luminance stretch amount is gradually reduced in the direction in which the score becomes zero. As described above, in the variety mode, the processing is performed by suppressing the luminance stretch amount in the enhancement processing.

  In the variety mode, the mapping unit 3 uses the same method as that of the first embodiment shown in FIG. 10 according to the first and second threshold values and the stretch amount received from the light detection unit 2 to input video. The signal gain is adjusted. Specific processing of the light emission detection unit 2 and the mapping unit 3 is the same as that described with reference to FIG.

  Next, in the second embodiment, a case where the genre information is a movie will be described. FIG. 19 is a diagram illustrating a control curve of the score and the luminance stretch amount in the movie mode, and is also indicated by a broken line in the variety mode.

In the case of the movie mode, as shown by a control curve U3 in FIG. 19, a threshold value B ′ higher than the threshold value B of the score in the standard mode or the variety mode is set, and the luminance stretch amount is constant above the threshold value B ′. For example, 800 cd / cm ² is set. Further, when the score is smaller than the threshold value B ′, the luminance stretch amount is gradually decreased in the direction in which the score becomes zero. As described above, in the movie mode, the luminance stretch amount in the enhancement processing is suppressed as compared with the normal mode, and the threshold value of the score at which the luminance stretch amount is 800 cd / cm ² is increased.

  In the movie mode, the mapping unit 3 adjusts the gain of the input video signal in the same manner as in the first embodiment shown in FIG. The specific processing of the light emission detection unit 2 and the mapping unit 3 is the same as that described with reference to FIG.

  As described above, in the movie mode, the luminance stretch amount in the enhancement processing is suppressed from the normal mode and the variety mode, and the second threshold is shifted to the high luminance side to reduce the high luminance region to be handled as the light emitting portion. Further, the gradation in the low luminance region is suppressed in a wider range by shifting the first threshold value to the high luminance side. As a result, an image quality with enhanced contrast is obtained while preventing excessive glare.

  Next, in the second embodiment, the case of the news / animation mode will be described. FIG. 20 is a diagram showing a control curve of the score and the luminance stretch amount in the news / animation mode.

In the news / animation mode, as shown by the control curve U4 in FIG. 20, the luminance stretch amount is always set to, for example, 550 (cd / m ² ). In this case, since the luminance stretch amount is zero, the luminance stretch of the backlight is substantially not performed. In the news / animation mode, the gain of the input video signal is adjusted in the same manner as in the first embodiment shown in FIG. 14, but since the input gradation is equal to the output gradation, the gain is substantially increased. No adjustment is made. As a result, in the news / animation mode, the backlight luminance stretch and video signal processing are not performed, and the input video signal is displayed faithfully.

(Embodiment 3)
FIG. 21 is a diagram for explaining still another embodiment (Embodiment 3) of the video display apparatus according to the present invention, and shows still another configuration example of the main part of the video display apparatus.

  The third embodiment has the same configuration as that of the second embodiment and performs the same operation as that of the second embodiment. However, unlike the second embodiment, the area active control is performed instead of the area active control / luminance stretch unit 5. There is no luminance stretch part 5a. In the luminance stretch unit 5a, the luminance of the backlight unit 7 is stretched based on the luminance stretch amount output from the mapping unit 3 of the signal processing unit 1.

  That is, the luminance stretch unit 5 a receives the video signal to which the tone mapping generated by the mapping unit 3 is applied, and outputs display control data for displaying the video signal to the display control unit 8. At this time, processing by area active control is not performed. On the other hand, the entire backlight unit 7 is uniformly stretched based on the luminance stretch amount output from the mapping unit 3.

  As a result, the bright image that is emitted becomes brighter and more radiant. In addition, since the luminance corresponding to the luminance stretch is reduced by the video signal processing in the non-light emitting part, as a result, the luminance of the light emitting part is increased on the screen, and high contrast and high quality images are displayed. Can do. The operation of the other components in the third embodiment, including the process of switching the control curve that defines the relationship between the index related to brightness and the stretch amount for stretching the luminance of the light source, is performed according to the genre information of the input video signal. Since it is the same as that of the form 2, repeated description is abbreviate | omitted.

  Also in the first embodiment, instead of the area active control / luminance stretch unit 5 of FIG. 1, a luminance stretch unit 5 a that similarly does not execute the area active control may be provided. In the case of such a configuration, the luminance stretch unit 5a determines an average lighting rate based on, for example, an index related to brightness, such as an average gradation value of the entire screen of the video signal, and calculates Max luminance from the average lighting rate. What is necessary is just to raise | generate the light emission brightness | luminance of LED based on it, and to feed back the Max brightness | luminance to the mapping part 3.

(Other features)
In each of the above examples, in the light emission portion detection processing in the light emission detection unit 2, the luminance Y is used as the feature amount of the video, and a luminance histogram is generated and the light emission portion is detected from the luminance histogram. However, as a feature value for generating a histogram, in addition to luminance, for example, CMI (Color Mode Index) or the highest gradation value (Max RGB) among gradation values of RGB video signals constituting one pixel. Can be used.

CMI is an index indicating how bright the color of interest is. Here, the CMI is different from the luminance, and indicates the brightness in consideration of the color information. CMI is defined by the following equation (6).
(L ^* / L ^* modeboundary) × 100 (6)

The above L ^* is an indicator of relative color brightness, and when L ^* = 100, the brightness of the brightest white as the object color is obtained. In the above formula (6), L ^* is the lightness of the color of interest, and L ^* modeboundary is the lightness of the boundary that appears to emit light with the same chromaticity as the color of interest. Here, it is known that L ^* modeboundary≈lightness of the brightest color (the lightest color of the object color). The lightness of the color where CMI = 100 is called the emission color boundary, and it is defined as emitting light when CMI = 100 is exceeded.

A method for calculating the CMI from the broadcast video signal to be displayed on the video display device will be described with reference to FIG. Broadcast video signal is BT. Standardized based on the 709 standard and transmitted. Therefore, the RGB data of the broadcast video signal is first converted to BT. The data is converted into tristimulus value XYZ data using a conversion matrix for 709. Then, the brightness L ^* is calculated from Y using a conversion formula. It is assumed that the color L ^{* of} interest is at position PL1 in FIG. Next, chromaticity is calculated from the converted XYZ, and L ^* (L ^* modeboundary) of the brightest color having the same chromaticity as the target color is examined from the already known brightest color data. The position on FIG. 22 is PL2.

From these values, the CMI is calculated using the above equation (6). CMI is indicated by the ratio of the optimal color of ^L * ^(L * ^{modeboundary)} of ^{L *} and chromaticity of the pixel of interest.
The CMI is obtained for each pixel of the video signal by the above method. Since it is a standardized broadcast signal, all pixels have a CMI in the range of 0-100. Then, for one frame image, a CMI histogram is created with the horizontal axis as CMI and the vertical axis as frequency. Here, the average value Ave and the standard deviation σ are calculated, and each threshold value is set to detect the light emitting portion.

  Max RGB is data having the maximum gradation value among RGB data. In the combination of RGB, the fact that two colors have the same chromaticity is synonymous with the fact that the ratio of RGB does not change. That is, the process of calculating the brightest color of the same chromaticity in the CMI is a process of obtaining a combination of RGB when the gradation of the RGB data becomes the maximum when the RGB data is multiplied by a certain value without changing the ratio.

For example, a pixel having gradation RGB data as shown in FIG. When the RGB data of the pixel of interest is multiplied by a certain number, as shown in FIG. 23B, when RGB is first saturated, the color is the brightest color with the same chromaticity as the original pixel. When the gradation of the target pixel of the first saturated color (R in this case) is r1 and the gradation of the brightest R is r2, a value similar to CMI can be obtained by the following equation (7). . The color that first saturates when it is multiplied by a certain value to RGB is the color having the maximum gradation among the RGB of the pixel of interest.
(R1 / r2) × 100 (7)

  Then, a value is calculated by the above equation (7) for each pixel to create a histogram. The average value Ave and the standard deviation σ are calculated from this histogram, and each light emission part can be detected by setting each threshold value.

  As described above, the embodiment of the present invention has been described by taking the standard program, variety, movie, news and animation as examples of the genre of the input video signal. However, for other genres, a desired image quality is obtained in the genre. Thus, the control curve that determines the relationship between the brightness-related index and the luminance stretch amount of the light source may be switched.

DESCRIPTION OF SYMBOLS 1 ... Signal processing part, 2 ... Light emission detection part, 3 ... Mapping part, 4 ... Genre information detection part, 5 ... Area active control and luminance stretch part, 5a ... Luminance stretch part, 6 ... Backlight control part, 7 ... Back light Light unit, 8 ... display control unit, 9 ... display unit.

Claims (7)

A display unit that displays an input video signal; a light source that illuminates the display unit; a control unit that controls the display unit and the light source; and a genre information detection unit that detects genre information of the input video signal. A video display device,
The control unit stretches and increases the luminance of the light source based on an index related to brightness calculated based on a predetermined condition from the input video signal, and further relates to the brightness of the input video signal. A histogram in which the number of pixels is integrated for a predetermined feature amount is generated, an upper region of the predetermined range of the histogram is detected as a light emitting portion, and the luminance of a video signal in a non-light emitting portion excluding the light emitting portion is reduced. The display brightness of the light emitting part is enhanced, and the control curve that determines the relationship between the brightness-related index and the brightness stretch amount that stretches the brightness of the light source is switched according to the genre information. Video display device. The video display device according to claim 1,
The control unit divides the image based on the input video signal into a plurality of regions, and based on the gradation value of the video signal of the divided region that is the divided region, the control unit determines the region of the light source corresponding to each divided region. Change the lighting rate,
The control curve is based on the average lighting rate obtained by averaging the lighting rates of the light source regions for all the light source regions, and the maximum display luminance that can be taken on the screen of the display unit that is related in advance to the average lighting rate. A control curve that defines the relationship with the displayed brightness stretch amount,
The video display device, wherein the control unit uses the average lighting rate as an index related to the brightness, and stretches the luminance of the light source based on the luminance stretch amount determined according to the average lighting rate. The video display device according to claim 1,
The control curve includes a score indicating a degree of brightness calculated by weighting the brightness of each pixel and counting the number of pixels for an image in a predetermined range including the detected light emitting portion area, and the luminance A control curve that defines the relationship with the stretch amount,
The control unit uses the score as an index related to the brightness, and stretches the luminance of the light source based on a luminance stretch amount corresponding to the score calculated from the input signal. apparatus. The video display device according to claim 2 or 3,
The control unit performs video processing to convert and output the input gradation of the input video signal,
The input / output characteristics that define the relationship between the input gradation and the output gradation have a threshold value that is determined in the region of the non-light emitting portion having a lower gradation than the boundary between the light emitting portion and the non-light emitting portion
The control unit determines in advance a gain at which an output gradation is reduced with respect to an input gradation of an input video signal in accordance with the luminance stretch amount, and applies the determined gain to a region having a gradation lower than the threshold. And performing the video processing, and changing the threshold based on the genre information in the video processing. In the video display device according to any one of claims 1 to 4,
When the average value of the histogram is A and the standard deviation is σ,
thresh = A + Nσ (N is a constant)
An image display device characterized in that the above pixel is a light emitting portion. The video display device according to any one of claims 1 to 5,
The video display device, wherein the control unit reduces an increase in display luminance of the display unit due to a luminance stretch of the light source in the non-light-emitting portion by a decrease in luminance of the input video signal.   A television receiver comprising the video display device according to claim 1.