JP5330552B2 - Video display device and television receiver - Google Patents

Abstract

The present invention makes possible video expressions with an enhanced sense of luster and contrast for video signals, while suppressing the sense of luster and contrast in cases of displaying video images obtained from websites or the like. This video display device comprises: a display unit (8); a backlight unit (6); a control unit (a signal processing unit (1); an area-active control/luminance stretch unit (4)) that controls the display unit (8) and the backlight unit (6); and a video type determination unit (14). The control unit executes or halts a light-emitting-section enhancement process in accordance with the result of determination by the video type determination unit (14). In the light-emitting-section enhancement process, the display luminance of a light-emitting section is enhanced by: creating a histogram in which the number of pixels is integrated for a predetermined characteristic amount related to the brightness of an input video signal; detecting an upper region within a predetermined range of the histogram as the light-emitting section; stretching and increasing the luminance of the backlight unit (6); and reducing the luminance of the video signal, within said input video signal, of non-light-emitting sections other than said light-emitting section.

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 Laid-Open No. 9-80378

  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, and the gradation of the high part is expanded and lifted, or the gradation of the low part is compressed Then, a process such as dropping 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.

  The enhancement function described in Patent Document 1 described above is for adjusting the contrast for the purpose of compensating for the change in brightness caused by the brightness adjustment of the backlight device. (Enhancement)

  Here, recent video display devices have various types of external input terminals, but many of them have LAN (Local Area Network) terminals and DVI (Digital Visual Interface) terminals as standard equipment. It is possible to connect to a Web site on the Internet via the PC, or connect to a PC (personal computer) via the DVI terminal. Then, the video display device can acquire a video from a Web site or a PC, and can display the acquired video on the screen.

  Usually, images acquired from websites or PCs are often still images that do not move, and if such still images are excessively brightened or the contrast is improved, it will be glaring, On the contrary, it may be difficult to see the video. In other words, when the above-described light-emitting partial enhancement processing is applied to a still image that does not move, the sense of contrast is improved and the sense of brightness is increased. It is desirable to suppress it.

  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. Obtained from websites and PCs while reducing the brightness of the video signal and enhancing the display brightness of the light emitting part to make it stand out and display images with enhanced brightness and contrast. An object of the present invention is to provide a video display device and a television receiver capable of suppressing the feeling of brightness and contrast when displaying a video.

In order to solve the above-described problems, a first technical means of the present invention includes a display unit that displays an input video signal, a light source that illuminates the display unit, a display unit, and a control unit that controls the light source. A video type determination unit that determines the type of the input video signal, a first input unit that inputs the video signal from the network, and a second that inputs the video signal from the information processing device. An input unit, a third input unit that inputs a video signal included in the broadcast signal, and a fourth input unit that inputs a video signal from a playback device , and the control unit includes: Depending on the determination result, light emission partial enhancement processing is executed or stopped, and the light emission partial enhancement processing 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. , The histogram By detecting an upper region of a predetermined range as a light emitting part, stretching and increasing the luminance of the light source, and reducing the luminance of a video signal of a non-light emitting part excluding the light emitting part of the input video signal, the light emission The display luminance of the portion is enhanced , and the light emitting portion has an average value of the histogram as A and a standard deviation as σ,
thresh = A + Nσ (N is a constant)
In the above-described pixel, the video type determination unit may determine whether the input video signal is the first input unit, the second input unit, the third input unit, or the fourth as the type of the input video signal. The control unit determines whether the input video signal is input from the first input unit or the second input unit by the video type determination unit. When the video signal is determined to be a video signal, the light emission partial enhancement process is stopped, and the video type determination unit inputs the input video signal from the third input unit or the fourth input unit. When it is determined that the signal is a video signal, the light emission partial enhancement process is executed .

The second technical means is a video display device including a display unit that displays an input video signal, a light source that illuminates the display unit, and a control unit that controls the display unit and the light source. Video type determination unit for determining the type of video signal, a first input unit for inputting a video signal from a network, a second input unit for inputting a video signal from an information processing device, and a video signal included in the broadcast signal A third input unit that inputs a video signal and a fourth input unit that inputs a video signal from the playback device, and the control unit executes a light emission partial enhancement process according to a determination result of the video type determination unit Alternatively, the light emission partial enhancement processing 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 the upper region of the predetermined range of the histogram is set as the light emission portion. As The display luminance of the light emitting part is enhanced by stretching and increasing the luminance of the light source and lowering the luminance of the video signal of the non-light emitting part excluding the light emitting part of the input video signal. , Where the light emitting portion is A when the average value of the histogram is A and the standard deviation is σ,
thresh = A + Nσ (N is a constant)
In the above-described pixel, the video type determination unit may determine whether the input video signal is the first input unit, the second input unit, the third input unit, or the fourth as the type of the input video signal. If it is determined whether the input video signal is a video signal input from the first input unit or the second input unit. Further, it is determined whether or not the input video signal is a still image, and the control unit performs the light emission partial enhancement process when the video type determination unit determines that the input video signal is a still image. When the video type determination unit determines that the input video signal is a video signal input from the third input unit or the fourth input unit, the light emission partial enhancement process is executed. Special to do It is obtained by the.

According to a third technical means, in the first or second technical means, the control unit divides the image based on the input video signal into a plurality of regions, and the gradation of the video signal in the divided region which is the divided region. Based on the value, the lighting rate of the light source region corresponding to the divided region is changed, and an average lighting rate is obtained by averaging the lighting rate of the light source region for all the light source regions. The luminance of the light source is stretched based on the maximum display luminance that can be taken on the screen of the display unit that is related in advance.

According to a fourth technical means, in any one of the first to third technical means, the control unit weights the brightness of each pixel with respect to an image in a predetermined range including the detected light emitting portion area. Then, a score indicating the degree of brightness is calculated by counting the number of pixels, and the luminance of the light source is stretched according to the score.

According to a fifth technical means, in any one of the first to fourth technical means, in the non-light-emitting portion, the control unit calculates an increase in display luminance of the display unit due to a luminance stretch of the light source. The input video signal is reduced by lowering the luminance.

The sixth technical means is a television receiver provided with the video display device of any one of the first to fifth 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. By enhancing the display brightness of the light emitting part (light emitting part enhancement processing) and making it stand out, it is possible to display images with enhanced brightness and contrast, and depending on the type of video signal Thus, for example, if the image is acquired from an Internet website or a PC, the light emission partial enhancement process is stopped to display an image with reduced brightness and contrast. be able to.

BRIEF DESCRIPTION OF THE DRAWINGS 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 for demonstrating the process example in the area active control and brightness | luminance stretch part of the video display apparatus of FIG. It is a figure which shows an example of the still image content displayed on the video display apparatus of FIG. 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. FIG. 5 is a diagram for explaining an average lighting rate of the backlight and a gradation value of a pixel in FIG. 4. It is a figure which shows the example of the Y histogram produced | generated from the luminance signal Y of the input video signal. 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. It is a figure 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 for demonstrating other embodiment of the video display apparatus based 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 example of a setting of the luminance stretch according to the pixel more than a 3rd threshold value. It is a figure for demonstrating other embodiment of the video display apparatus based 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, an area active control / luminance stretch unit 4, a backlight control unit 5, a backlight unit 6, a display control unit 7, a display unit 8, a tuner 9, an HDMI (High A definition multimedia interface (LAN) terminal 10, a local area network (LAN) terminal 11, a digital visual interface (DVI) terminal 12, a selector 13, a video type determination unit 14, and a remote control signal processing unit 15. 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 6 and the display unit 8 are controlled. The signal processing unit 1, the area active control / luminance stretch unit 4, the backlight control unit 5, and the display control. Part 7 is applicable.

  A video signal input from any of the tuner 9, the HDMI terminal 10, the LAN terminal 11, and the DVI terminal 12 is input to the signal processing unit 1 and the area active control / luminance stretch unit 4 via the selector 13. At this time, the video signal to the area active control / luminance stretch unit 4 is input to the area active control / luminance stretch unit 4 after applying the tone mapping generated by the mapping unit 3 of the signal processing unit 1.

  First, a case where a video signal is input via the tuner 9 or the HDMI terminal 10 will be described. In the case of the tuner 9, the input video signal is a video signal separated from the broadcast signal received by the tuner 9. In the case of the HDMI terminal 10, the input video signal is reproduced by a playback device such as a recorder or a player connected to the HDMI terminal 10 via HDMI. This is a video signal when an HDD or an external recording medium (BD, DVD, etc.) is reproduced. The area active control / luminance stretch unit 4 divides the image based on the video signal into predetermined areas according to 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 6 is calculated. The lighting rate is determined for each region of the backlight unit 6 corresponding to the divided region of the video, and the lighting rate referred to here is actually changed as described later, and can be said to be a temporary value. .

  Moreover, the backlight part 6 is an example of the light source for illuminating the display part 8, is comprised by several LED, and brightness | luminance control is possible for every area | region. The lighting rate for each area of the backlight unit 6 is determined based on a predetermined arithmetic expression, but is basically maintained without decreasing the luminance of the LED in an area 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. Instead of the region having the 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 4 calculates the overall average lighting rate of the backlight unit 6 from the lighting rate of each region, and according to the average lighting rate, the backlight unit 6 is calculated by a predetermined arithmetic expression. The maximum amount of light emission luminance stretch (hereinafter referred to as luminance stretch amount) is calculated. By stretching the maximum light emission luminance of the backlight unit 6 (the maximum light emission luminance of the LED) by this luminance stretch amount, the maximum screen luminance that can be obtained 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 is determined according to the average lighting rate as illustrated in the graph of FIG. Value. FIG. 2 is a diagram for explaining an example of processing in the area active control / luminance stretch unit 4 and shows the relationship of the Max luminance (cd / m ² ) to the average lighting rate (window size) of the backlight unit 6. An example of a graph is shown.

In the graph 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. . Even if there is a scene where the luminance stretch amount becomes negative depending on the average lighting rate as in this example, the integrated value obtained by integrating the Max luminance graph of FIG. 2 over all the average lighting rates is the reference luminance. Since it is larger than the integral value integrated over all average lighting rates, 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 4 changes the lighting rate (temporary lighting rate) for each of the above areas 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 8 associated in advance with the average lighting rate. It is preferable to stretch the luminance.

  Furthermore, the area active control / luminance stretch unit 4 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 portion 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 4. 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 lower the luminance corresponding to the luminance stretch of the backlight unit 6 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 4.

Further, the area active control / luminance stretch unit 4 outputs control data for controlling the backlight unit 6 to the backlight control unit 5, and the backlight control unit 5 performs the control of the backlight unit 6 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 6 so that the lighting rate after stretching for each region described above is obtained. Control data to the backlight unit 6 at the time of displaying 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 six 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 6 is performed by PWM (Pulse Width Modulation) control, it can also be controlled so that it may become a desired value by electric current control or these combination.

Further, the area active control / luminance stretch unit 4 outputs display control data for controlling the display unit 8 to the display control unit 7, and the display control unit 7 displays the display unit 8 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 8 to display. The display unit 8 is a liquid crystal panel that is illuminated by the LED of the backlight unit 6 and displays an image.

  Thus, the area active control / luminance stretch unit 4 stretches the backlight luminance in accordance with the average lighting rate to increase the luminance of the LED of the backlight unit 6, and information on the luminance stretch (the above Max luminance). Is returned to the signal processing unit 1 to reduce the luminance corresponding to the luminance stretch of the backlight unit 6 with respect to the video signal. The luminance stretch is applied to the entire backlight unit 6, 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 4, the backlight luminance is stretched to increase the luminance of the LED of the backlight unit 6, and the luminance of the video signal of the non-light emitting portion of the input video signal is decreased. To enhance the display luminance of the light emitting portion (hereinafter, light emitting portion 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 6 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. That is, the area active control / luminance stretch unit 4 uses the increase in display luminance of the display unit 8 due to the luminance stretch of the light source in the non-light-emitting portion (that is, the predetermined region having a low predetermined feature amount). It is preferable to reduce the brightness.

  The main object of the present invention is to perform light emission partial enhancement processing on an input video signal to enhance the shine and contrast while displaying an image acquired from a website or a PC. It is to be able to suppress. As a configuration for this, the video display device includes a video type determination unit 14 that determines the type of the input video signal, and a signal processing unit 1 and an area active control / luminance stretch unit 4 that are examples of the control unit of the present invention. Prepare. The signal processing unit 1 and the area active control / luminance stretch unit 4 execute or stop the light emission partial enhancement process according to the determination result of the video type determination unit 14. Note that, as described above, the light emission partial enhancement processing 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 emits an upper region of the predetermined range of the histogram. The luminance of the light source is detected by stretching and increasing the luminance of the light source, and the luminance of the video signal of the non-light emitting portion of the input video signal excluding the light emitting portion is reduced, thereby enhancing the display luminance of the light emitting portion.

  In the example of FIG. 1, the video display device is a tuner 9 corresponding to the third input unit of the present invention that inputs a video signal included in a broadcast signal, and a video signal input from a playback device such as a recorder or a player. From the HDMI terminal 10 as an example of the fourth input unit of the invention, the LAN terminal 11 as an example of the first input unit of the present invention for inputting a video signal from a network such as the Internet, and the information processing apparatus (PC) And a DVI terminal 12 which is an example of a second input unit of the present invention for inputting a video signal. The video signal input from the tuner 9 or the HDMI terminal 10 mainly corresponds to the moving image content, and the video signal input from the LAN terminal 11 or the DVI terminal 12 mainly corresponds to the still image content. is there.

  The video type determination unit 14 is a video signal input from any input source of the input video signal, that is, any input source of the tuner 9, the HDMI terminal 10, the LAN terminal 11, and the DVI terminal 12 as the type of the input video signal. Determine if there is. Since the video signal input from the tuner 9 or the HDMI terminal 10 is mainly video content, the determination result including the execution instruction of the light emission partial enhancement process is output to the signal processing unit 1 and the area active control / luminance stretch unit 4. To do. Since the video signal input from the LAN terminal 11 or the DVI terminal 12 is mainly still image content, the determination result including the stop instruction of the light emission partial enhancement processing is used as the signal processing unit 1 and the area active control / luminance stretching unit 4. Output to.

  FIG. 3 is a diagram illustrating an example of still image content displayed on the video display device. 3A shows still image content acquired from a website on the Internet, and FIG. 3B shows still image content acquired from a PC. When the above-described light emission partial enhancement processing is applied to such still image content, the image has a strong shine and contrast, and is difficult to view. Therefore, the signal processing unit 1 and the area active control / luminance stretch unit 4 are configured to emit light when the video type determination unit 14 determines that the input video signal is a video signal input from the LAN terminal 11 or the DVI terminal 12. Stop enhancement processing. This is because the video signal input from the LAN terminal 11 or the DVI terminal 12 mainly corresponds to still image content.

  Further, the signal processing unit 1 and the area active control / luminance stretch unit 4, when the video type determination unit 14 determines that the input video signal is a video signal input from the tuner 9 or the HDMI terminal 10, the light emission partial enhancement. Execute the process. This is because the video signal input from the tuner 9 or the HDMI terminal 10 mainly corresponds to the moving image content. That is, the type of the input video signal is determined by the input source (tuner input, HDMI input, LAN input, DVI input in the above example), and in the case of LAN input or DVI input, the light emission partial enhancement process is stopped and the tuner input is stopped. Or, in the case of HDMI input, light emission partial enhancement processing is executed.

  In FIG. 1, it is assumed that the tuner 9 is selected as an input destination and the user is watching a digital broadcast program. In this case, since the tuner 9 is selected, the light emission partial enhancement process is executed. Here, for example, in order for the user to view a video on a website on the Internet, a remote control signal for operating the remote control R to switch the input to the Internet (LAN terminal 11) is transmitted to the video display device. The remote control signal processing unit 15 of the video display device includes a remote control light receiving unit (not shown), analyzes the remote control signal received from the remote control R, and instructs the selector 13 to switch the input to the LAN terminal 11. The selector 13 selects the LAN terminal 11 in accordance with an instruction from the remote control signal processing unit 15 and switches the input to the selected LAN terminal 11.

  When the user operates the remote controller R to activate the Web browser, the video display device is connected to the Internet via the LAN terminal 11, and the video display device displays a video of a website on the Internet. At this time, the selector 13 notifies the video type determination unit 14 that the LAN terminal 11 is selected as an input destination, and the video type determination unit 14 that has received this notification inputs the input video signal from the LAN terminal 11. It is determined that the received video signal is a video signal, and a determination result including a light emission partial enhancement process stop command is output to the signal processing unit 1 and the area active control / luminance stretch unit 4.

  The signal processing unit 1 and the area active control / luminance stretch unit 4 stop the light emission partial enhancement process according to the determination result. When the light emission partial enhancement processing is stopped, the signal processing unit 1 stops the processing in the light emission detection unit 2, and the mapping unit 3 uses, for example, a default tone mapping (for example, input / output corresponds to one-to-one. Tone curve) to the multiplier. Further, the area active control / luminance stretch unit 4 stops the processing related to area active control and luminance stretch, and sends control data for controlling the backlight unit 6 to the backlight control unit 5 for the input video signal. In addition to outputting, display control data for controlling the display unit 8 is output to the display control unit 7. As these control data and display control data, for example, default setting data can be used.

  The area active control is to divide the video into a plurality of predetermined areas (areas) and control the light emission luminance of the LED for each divided area, but even when the light emission partial enhancement process is stopped, This area active control may be executed. For example, as shown in FIG. 4C, which will be described later, the maximum gradation value of the video signal is extracted for each divided region, and the LED lighting rate (drive duty) for each region is determined according to the extracted maximum gradation value. decide. In this case, since the luminance stretch is not performed, the process of stretching the backlight luminance according to the Max luminance obtained from the average lighting rate is stopped. Accordingly, the process of feeding back the luminance stretch information (Max luminance) from the area active control / luminance stretch unit 4 to the signal processing unit 1 is also stopped.

  Thus, when displaying the video of the website via the LAN terminal 11, the light emission partial enhancement process can be stopped, so that the video with reduced brightness and contrast can be displayed. Similarly, when the user operates the remote controller R to switch the input to the PC (DVI terminal 12) in order to view the video of the PC, the light emission by the signal processing unit 1 and the area active control / luminance stretch unit 4 is also performed. Partial enhancement processing is stopped.

  In the embodiment described above, the type of the input video signal is determined by the input source (tuner input, LAN input, DVI input, HDMI input, etc.), and in the case of LAN input or DVI input, the light emission partial enhancement process is stopped. However, there may be a case in which a moving image is played back on a PC even with DVI input, or a case in which a moving image is played back on the Internet even with LAN input. Then, it is desirable that the user can switch execution / stop of the light emission partial enhancement process according to his / her preference. For example, an operation button for switching execution / stop of the light emission partial enhancement processing may be provided on the remote controller R in FIG. When the light emission partial enhancement processing is stopped, the remote control signal processing unit 15 receives the remote control signal for switching the light emission partial enhancement processing to execution from the remote control R, so that the signal processing unit 1 executes the light emission partial enhancement processing. The area active control / luminance stretch unit 4 is instructed.

  Another embodiment will be described. As described above, even in the case of LAN input or DVI input, moving image content may be input. Therefore, the video display device may determine whether or not the input video signal is a still image. Specifically, when the video type determination unit 14 determines that the input video signal is a video signal input from the LAN terminal 11 or the DVI terminal 12, it further determines whether or not the input video signal is a still image. Determine. The signal processing unit 1 and the area active control / luminance stretch unit 4 stop the light emission partial enhancement processing when the video type determination unit 14 determines that the input video signal is a still image.

  For the still image determination, for example, the sum of absolute values of differences in pixel values (SAD: Sum Of Absolute Difference) can be used. This SAD is one of the indices when detecting a motion vector. The smaller the SAD between two frames, the higher the degree of similarity between these two frames, which can be regarded as a still image. That is, SAD is obtained between two frames. When SAD is smaller than a predetermined value, it is determined as a still image, and when SAD is equal to or greater than a predetermined value, it can be determined as a moving image.

  In this way, in addition to determining the input source, still image determination makes it possible to more reliably discriminate between a moving image and a still image. On the other hand, the light emission partial enhancement process can be stopped.

  When the video display device as described above is configured as a television receiving device, the television receiving device selects and demodulates a broadcast signal received by an antenna, decodes it, and generates a playback video signal (FIG. 1). Corresponding to the tuner 9), and appropriately performing predetermined image processing on the reproduction video signal and inputting it as the input video signal of FIG. 1. Thereby, the received broadcast signal can be displayed on the display unit 8. 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. 4 is a diagram for explaining a calculation process example of the average lighting rate in the area active control / luminance stretch unit 4, and FIG. 5 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 4 divides one frame of video into a plurality of predetermined areas (the above-mentioned areas) based on the input video signal, and the LEDs corresponding to the divided areas are displayed. The light emission luminance is controlled for each divided region.

  First, the area active control / luminance stretch unit 4 divides the image area of the entire screen into 12 parts in the vertical direction and 12 parts in the horizontal direction as shown in FIG. Divide into 144 regions. In addition, it is assumed that at least one LED is provided for each region as the backlight unit 6.

  Then, the area active control / luminance stretch unit 4 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. 4B, 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. 4C 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. 4D shows the lighting rate of each area and the average lighting rate of the entire screen. 4 (C) and 4 (D), an example in which the screen of one frame is divided into eight areas (areas Nos. 1 to 8) is given for the sake of simplicity, but as shown in FIG. 4 (B). Processing can be performed by dividing into a large number of regions, and processing can be performed by dividing the region into as many regions as the number of LEDs provided.

  First, for each of the areas No. 1 to No. 8, the lighting rate of the temporary LED of the backlight of the area is calculated from the maximum gradation value in the area. The provisional lighting rate can be indicated by, for example, LED drive duty (hereinafter, 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, a predetermined luminance may be obtained by increasing the current value together with the current control.

  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 8 (here, the LCD panel) 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. 5A, the maximum gradation value is 128. In this case, as shown in FIG. 5B, the lighting rate of the backlight in the area is (1 / ( 255/128)) ^2.2 = 0.217 times (21.7%). The area active control / luminance stretch unit 4 determines such a provisional lighting rate, and considers the gradation value for each pixel in the display unit 8 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. 5C 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% of the above case, but the luminance stretch portion (correctly, 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 7 may perform display control of the display unit 8 with the display control data of the gradation value illustrated in FIG. 5C for the pixel group illustrated in FIG.

  In the example of FIG. 4C, 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 region indicated by the gray scale. FIG. 4D is a graph in which the percentages in FIG. 4C 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 4 averages the temporary lighting rate of the backlight for each area calculated from the maximum gradation value of the video signal, and calculates the average lighting rate of the backlight unit 6 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. 4D, and the actual value is about 53%.

  The actual luminance of the backlight unit 6 is determined based on the maximum light emission luminance value (maximum light 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 graph of FIG. 2 is the average lighting rate (window size) of the backlight, and this average lighting rate is calculated between 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. 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.

In FIG. 2, when the average lighting rate is P, the value of Max luminance is the largest, and the maximum screen luminance 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.

  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 4 stretches the luminance of the backlight according to the curve of FIG. 2 and outputs the control signal to the backlight control unit 5. 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 4 is applied with tone mapping generated by signal processing performed by the signal processing unit 1 described below, with the gain of the low gradation region being reduced. 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 4 outputs the Max luminance value obtained from the average lighting rate of the backlight according to the 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 4.

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. 6 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. 7 is a diagram illustrating an example of tone mapping generated by the mapping unit 3. In FIG. 7, the horizontal axis represents the input gradation of the luminance value of the video, and the vertical axis represents 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. Therefore, the light emission detection unit 2 sets and detects the first threshold Th1, sets the first gain G1 for a region smaller than Th1, and sets the second gain so as to linearly connect Th1 and Th2. Tone mapping is performed by setting the gain G2.

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 4. 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. Max luminance output from 4. 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. 7 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 portion is suppressed based on the luminance stretch amount of the backlight is input to the area active control / luminance stretch unit 4.

FIG. 8 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 4. The graph shown in FIG. 8 is the same as the graph shown in FIG.

As described above, the area active control / luminance stretch unit 4 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. 7, 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. 7, 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. 8, 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. 9 is a diagram illustrating a state in which the screen luminance is enhanced by the processing of the area active control / luminance stretch unit 4. In FIG. 9, 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 8, and S 2 and S 3 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 4. 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 4.

  In this way, when the input video signal is between 0 gradation (S1) and S2, the screen brightness is controlled with the reference brightness. In the case of dark images with low gradation, if the brightness is increased and displayed, the image quality will be reduced by the video signal processing by the amount of the backlight brightness stretch. Try not to go up.

  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. .

(Embodiment 2)
FIG. 10 is a diagram for explaining another embodiment (Embodiment 2) of the video display device according to the present invention, and shows another configuration example of the main part of the video display device.

  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 4. The light emission detection unit 2 determines the luminance stretch amount based on the detection result of the light emission portion, and the mapping unit 3 executes tone mapping based on the determined luminance stretch amount. Therefore, the mapping unit 3 of the signal processing unit 1 does not need to output the Max luminance value by luminance stretching from the area active control / luminance stretching unit 4 as in the first embodiment. Of course, the light emission detection unit 2 may only detect the light emission part, and the mapping unit 3 may be configured to calculate the luminance stretch amount from the detection result of the light emission part.

  FIG. 11 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. As in 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, 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. 12 is a diagram illustrating a setting example of the luminance stretch according to the pixels having the third threshold Th3 or more. 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, The degree of brightness is indicated by weighting and calculating the distance from the threshold Th3. For example, it is calculated by 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. 11, 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 a graph U1 in FIG. 12, when the score is higher than a certain level, the luminance stretch amount is set high, and a high gradation shining image is stretched to a higher luminance to increase the shine. 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, as shown in FIG. 7, the first gain G1 is set for a region smaller than Th1 detected by the light emission detector 2, and the second gain G2 is set so as to linearly connect Th1 and Th2. To do. 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 input to the area active control / luminance stretch unit 4.

  The processing in the area active control / luminance stretch unit 4 is the same as in the first embodiment. However, the area active control / luminance stretch unit 4 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 light emission of the signal processing unit 1 Based on the luminance stretch amount detected by the detection unit 2, the luminance of the LED of the backlight unit 6 is stretched.

  That is, the area active control / luminance stretch unit 4 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 according to the luminance stretch amount, and the entire luminance of the backlight is increased. 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 high-quality image is displayed. be able to. The relationship between the input video signal and the screen luminance is the same as that in FIG. 9 shown in the first embodiment.

  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. Then, a score indicating the degree of brightness is calculated, a luminance stretch amount is determined according to the score, and the area active control / luminance stretch unit 4 is stretched by the luminance stretch amount. Therefore, the luminance stretch amount is output to the area active control / luminance stretch unit 4 and the mapping unit 3. The area active control / luminance stretch unit 4 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.

  Then, the signal processing unit 1 and the area active control / luminance stretch unit 4 execute or stop the light emission partial enhancement processing according to the second embodiment according to the determination result of the video type determination unit 14. Since the configuration of the video type determination unit 14 according to the present invention is the same as that of the first embodiment, repeated description thereof is omitted here.

  When the light emission partial enhancement process is stopped, the signal processing unit 1 stops the process in the light emission detection unit 2, so the luminance stretch amount (N) is not calculated, and the mapping unit 3 and the area active control / luminance stretch unit 4 are not calculated. The luminance stretch amount (N) is not output to. In this case, the mapping unit 3 outputs, for example, a default tone mapping (for example, a tone curve corresponding to one-to-one input / output) to the multiplier. Further, the area active control / luminance stretch unit 4 stops the processing related to area active control and luminance stretch, and sends control data for controlling the backlight unit 6 to the backlight control unit 5 for the input video signal. In addition to outputting, display control data for controlling the display unit 8 is output to the display control unit 7. As these control data and display control data, for example, default setting data can be used.

  The area active control may be executed in the same manner as in the first embodiment. For example, as shown in FIG. 4C described above, the maximum gradation value of the video signal is extracted for each divided region, and the lighting rate (drive duty) of the LED for each region is determined according to the extracted maximum gradation value. decide. In this case, since the luminance stretch is not performed, the process of stretching the backlight luminance according to the Max luminance obtained from the average lighting rate is stopped.

(Embodiment 3)
FIG. 13 is a view 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 4. There is no luminance stretch part 4a. In the luminance stretch unit 4a, the luminance of the backlight unit 6 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 4 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 7. At this time, processing by area active control is not performed. On the other hand, the entire backlight unit 6 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.

  Then, the signal processing unit 1 and the luminance stretch unit 4a execute or stop the light emission partial enhancement processing according to the third embodiment according to the determination result of the video type determination unit 14. Since the configuration of the video type determination unit 14 according to the present invention is the same as that of the first and second embodiments, repeated description thereof is omitted here. When the light emission partial enhancement process is stopped, the signal processing unit 1 stops the process in the light emission detection unit 2, and thus the luminance stretch amount (N) is not calculated, and the mapping unit 3 and the luminance stretch unit 4a have the luminance stretch amount. (N) is not output.

  In this case, the mapping unit 3 outputs, for example, a default tone mapping (for example, a tone curve corresponding to one-to-one input / output) to the multiplier. In addition, the luminance stretch unit 4a stops the process related to the luminance stretch, outputs control data for controlling the backlight unit 6 to the backlight control unit 5 with respect to the input video signal, and displays the display unit 8 Display control data for control is output to the display control unit 7. As these control data and display control data, for example, default setting data can be used.

  In the first embodiment, instead of the area active control / luminance stretch unit 4 in FIG. 1, a luminance stretch unit 4 a that similarly does not execute the area active control may be provided. In such a configuration, Max luminance is obtained from the average lighting rate (however, in this example, the temporary lighting rate itself is the temporary average lighting rate of the entire screen) in the luminance stretch unit 4a, and the light emission luminance of the LED is based on that. And the Max luminance may be fed back to the mapping unit 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 amount 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. The broadcast video signal is standardized based on the BT.709 standard and transmitted. Accordingly, the RGB data of the broadcast video signal is first converted into tristimulus value XYZ data using a conversion matrix for BT.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. 14 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. 15B, the color when one of RGB is first saturated 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.

DESCRIPTION OF SYMBOLS 1 ... Signal processing part, 2 ... Light emission detection part, 3 ... Mapping part, 4 ... Area active control and luminance stretch part, 4a ... Luminance stretch part, 5 ... Backlight control part, 6 ... Backlight part, 7 ... Display control 8 is a display unit, 9 is a tuner, 10 is an HDMI terminal, 11 is a LAN terminal, 12 is a DVI terminal, 13 is a selector, 14 is a video type determination unit, and 15 is a remote control signal processing unit.

Claims (6)

A video display device comprising: a display unit that displays an input video signal; a light source that illuminates the display unit; and a control unit that controls the display unit and the light source,
Included in the broadcast signal is a video type determination unit that determines the type of the input video signal, a first input unit that inputs a video signal from a network, a second input unit that inputs a video signal from an information processing device, and the like. A third input unit for inputting the video signal, and a fourth input unit for inputting the video signal from the playback device ;
The control unit executes or stops the light emission partial enhancement process according to the determination result of the video type determination unit,
The light emission partial enhancement process generates a histogram in which the number of pixels is integrated for a predetermined feature amount related to the brightness of the input video signal, detects an upper region of the predetermined range of the histogram as a light emission part, Stretching and increasing the luminance of the light source, and enhancing the display luminance of the light emitting portion by reducing the luminance of the non-light emitting portion of the input video signal excluding the light emitting portion ,
The light-emitting portion has an average value of the histogram as A and a standard deviation as σ,
thresh = A + Nσ (N is a constant)
Or more pixels,
The video type determination unit receives the input video signal from the first input unit, the second input unit, the third input unit, or the fourth input unit as the type of the input video signal. To determine whether the video signal is
The control unit stops the light emission partial enhancement process when the video type determination unit determines that the input video signal is a video signal input from the first input unit or the second input unit. When the video type determination unit determines that the input video signal is a video signal input from the third input unit or the fourth input unit, the light emission partial enhancement process is executed. A video display device characterized by that. A video display device comprising: a display unit that displays an input video signal; a light source that illuminates the display unit; and a control unit that controls the display unit and the light source,
Included in the broadcast signal is a video type determination unit that determines the type of the input video signal, a first input unit that inputs a video signal from a network, a second input unit that inputs a video signal from an information processing device, and the like. A third input unit for inputting the video signal, and a fourth input unit for inputting the video signal from the playback device;
The control unit executes or stops the light emission partial enhancement process according to the determination result of the video type determination unit,
The light emission partial enhancement process generates a histogram in which the number of pixels is integrated for a predetermined feature amount related to the brightness of the input video signal, detects an upper region of the predetermined range of the histogram as a light emission part, Stretching and increasing the luminance of the light source, and enhancing the display luminance of the light emitting portion by reducing the luminance of the non-light emitting portion of the input video signal excluding the light emitting portion,
The light-emitting portion has an average value of the histogram as A and a standard deviation as σ,
thresh = A + Nσ (N is a constant)
Or more pixels,
The video type determination unit receives the input video signal from the first input unit, the second input unit, the third input unit, or the fourth input unit as the type of the input video signal. If the input video signal is a video signal input from the first input unit or the second input unit, the input video signal is further determined. Determines whether is a still image,
The control unit stops the light emission partial enhancement process when the video type determination unit determines that the input video signal is a still image, and the video type determination unit determines that the input video signal is the first video signal. 3. The video display apparatus according to claim 1 , wherein when the video signal is determined to be a video signal input from the third input unit or the fourth input unit, the light emission partial enhancement process is executed . The video display device according to claim 1 or 2 ,
The control unit divides an image based on the input video signal into a plurality of regions, and turns on the light source region corresponding to the divided region based on the gradation value of the video signal of the divided region which is the divided region. Change the rate,
Obtain an average lighting rate that averages the lighting rate of the light source region for all regions of the light source,
A video display device, wherein the luminance of the light source is stretched based on a maximum display luminance that can be taken on the screen of the display unit that is related in advance to the average lighting rate. In the video display device according to any one of claims 1 to 3 ,
The control unit calculates a score indicating the degree of brightness by weighting the brightness for each pixel and counting the number of pixels for an image in a predetermined range including the detected light emitting part region, and the score A video display device characterized by stretching the luminance of the light source according to the above. In the video display device according to any one of claims 1 to 4 ,
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. Television receiver including the display device according to any one of claims 1-5.

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