JP5174982B1 - Video display device and television receiver - Google Patents

Abstract

An object of the present invention is to detect a light emitting portion of a video signal, enhance the display luminance of the light emitting portion and display it, and control the luminance stretch according to the surrounding brightness state at this time, Improve the image quality by increasing the brightness.
A light emission detecting unit detects a light emitting unit regarded as a light emitting image based on a predetermined feature amount of a force image signal. The area active control / luminance stretch unit 14 stretches and increases the luminance of the backlight unit 16 based on an index related to brightness calculated based on a predetermined condition from the input video signal, and does not emit light except the light emitting unit. The luminance of the video signal of the part is reduced. At this time, the area active control / luminance stretch unit 14 switches the control curve that defines the relationship between the index related to the brightness and the stretch amount according to the brightness around the apparatus detected by the brightness detection unit 19.
[Selection] Figure 1

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 a luminance stretch function of a video signal and a backlight light source in order to improve the quality of a displayed video.

  In recent years, with regard to the display technology of a television receiver, a technology related to HDR (high dynamic range imaging) that faithfully reproduces and displays what exists in nature has been actively studied. One of the purposes of HDR is, for example, to reproduce a luminescent color portion such as fireworks or neon in a screen, and to give a sense of brightness.

  In this case, the emission color and the object color can be detected and separated by the emission detection function, and only the emission color on the screen can be brightened by signal processing and backlight emission luminance control. Here, in a video that changes variously, a portion that emits light relatively brightly is detected from the luminance distribution of the video, and the light emitting portion is consciously stretched to make the light emitting portion on the screen more prominent. The effect of improving the image quality can be obtained.

  As a conventional technique, for example, Patent Document 1 discloses a display device that achieves appropriate screen display luminance in accordance with the feature amount of an image and ambient brightness and sufficiently reduces power consumption. Has been. This display device has a liquid crystal panel that displays an image based on an input video signal, a backlight unit, and a brightness sensor for detecting the brightness around the device. Then, in accordance with the brightness detected by the brightness sensor, the brightness conversion characteristic that defines the light emission brightness of the backlight with respect to the feature amount (for example, APL) of the input video signal is changed. At this time, the change in the luminance conversion characteristic is such that the position of the characteristic change point, which is the point at which the light emission luminance decreases and the inclination of the luminance conversion characteristic changes as the surrounding of the liquid crystal display device becomes dark, is changed in the direction of change of the feature amount. Try to move it. Then, the light emission luminance of the backlight is controlled according to the obtained luminance conversion characteristic.

JP 2010-271480 A

As described above, in the HDR technology, by detecting a light emitting portion that is brightly shining on the screen and stretching the display luminance of the light emitting portion, the contrast is improved for the human eye, and the brightness It is possible to provide a high-quality display image.
However, the ambient brightness of the video display device changes according to time and environment, and the appearance of the display screen also changes according to the ambient brightness. When the HDR is operated under certain conditions regardless of the surrounding brightness state, depending on the image, it may be dazzling and uncomfortable, or the so-called black float may be conspicuous and the quality may be lowered.
For example, in a dark environment around the video display device, if the screen brightness is increased uniformly by HDR using signal processing and backlight brightness stretch, the feeling of dazzling becomes stronger due to the darkness of the surroundings, causing a sense of incongruity. There is a case. Also, when the environment is dark, so-called black floats become conspicuous due to the luminance stretch, and the visual quality may deteriorate. On the other hand, when the environment around the display device is bright, the dazzling feeling and the black floating are not so conspicuous. Therefore, the image quality can be improved by improving the contrast feeling and the brightness feeling by the luminance stretch.

  The video display device of Patent Document 1 changes the luminance conversion characteristic that defines the backlight emission luminance with respect to the feature amount (for example, APL) of the input video signal according to the brightness detected by the brightness sensor. Rather than detecting the light emitting part and stretching the brightness at that time, the light emitting part in the screen is made particularly prominent and bright, and at this time, the degree of brightness stretching is controlled according to the state of the device No idea is disclosed that suppresses the feeling of dazzling or prevents the deterioration of the image quality due to floating on the black.

  The present invention has been made in view of the above circumstances, and by detecting the light emitting portion of the video signal and stretching the display luminance of the light emitting portion to display it, the brightness can be further enhanced. An image display device that performs display with higher contrast and controls the luminance stretch according to the brightness of the surroundings of the image display device at this time, so that high-quality image expression without any sense of incongruity is always performed. And it aims at providing a television receiver.

  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. And the control unit, based on a control curve that defines a relationship between a brightness-related index calculated from the input video signal based on a predetermined condition and a luminance stretch amount for stretching the luminance of the light source, The luminance of the light source is stretched to increase, and the video signal of the non-light emitting part excluding the light emitting part is detected based on the predetermined feature amount of the input video signal, and the light emitting part regarded as the light emitting picture is detected. By reducing the brightness of the image display device, the display brightness of the light emitting unit is enhanced, the video display device has a brightness detection unit for detecting the brightness of the surroundings of the video display device, Control According brightness around the detected using the brightness detector the image display device, in which is characterized in that switching the control curve.

  The second technical means is a television receiver provided with the video display device of the first technical means.

  According to the video display device of the present invention, the light emitting portion of the video signal is detected, and the display brightness of the light emitting portion is stretched to be displayed so as to be displayed, thereby increasing the brightness and displaying with high contrast. In this case, by controlling the luminance stretch according to the black display state of the video at this time, it is possible to provide a video display device and a television receiver that can always express high-quality video.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining one Embodiment of the video display apparatus based on this invention, and shows the structure of the principal part of a video display apparatus. It is a figure explaining the control process of the light emission area | region in an area active control and a brightness stretch part. It is another figure explaining the control process of the light emission area | region in an area active control and brightness | luminance stretch part. It is a figure explaining the determination process of an average lighting rate concretely. It is a figure for demonstrating the process example of an area active control and a brightness | luminance stretch part. It is a figure which shows the example of the Y histogram produced | generated from the luminance signal Y. It is a figure which shows an example of the tone mapping which a mapping part produces | generates. It is a figure for demonstrating the Max brightness | luminance output by an area active control and brightness | luminance stretch part. It is a figure for demonstrating the example of control of the Max brightness | luminance changed according to the detection result of ambient brightness. It is a figure for demonstrating the other example of the example of control of the Max brightness | luminance changed according to the detection result of ambient brightness. It is a figure for demonstrating the further another example of the control example of the Max brightness | luminance changed according to the detection result of ambient brightness. It is a figure explaining the 1st threshold value changed according to the detection result of ambient brightness. It is a figure explaining the example of the tone mapping according to brightness detection. It is a figure which shows the state in which screen brightness | luminance is enhanced by the process of area active control and the brightness | luminance stretch part. It is a figure explaining other embodiment of the video display apparatus concerning this invention. An example of a Y histogram generated from a luminance signal Y of an input video signal is shown. It is a figure which shows the example of calculation of the luminance stretch amount according to the pixel more than 3rd threshold value Th3. It is a figure for demonstrating the example of a setting of the control curve of the luminance stretch amount changed according to the detection result of ambient brightness. It is a figure for demonstrating the other example of a control curve of the luminance stretch amount changed according to the detection result of ambient brightness. It is a figure explaining other embodiment of the video display apparatus concerning this invention. It is a figure for demonstrating the method of calculating CMI from the broadcast video signal which should be displayed with a video display apparatus. It is a figure for demonstrating the maximum gradation value of RGB used as a feature-value.

(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 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.
The video signal separated from the broadcast signal and the video signal input from the external device are input to the signal processing unit 11 and the area active control / luminance stretch unit 14. At this time, the tone mapping generated by the mapping unit 13 of the signal processing unit 11 is applied to the video signal to the area active control / luminance stretch unit 14 and then input to the area active control / luminance stretch unit 14.

  The light emission detection unit 12 of the signal processing unit 11 generates a histogram for each frame based on the feature amount 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.

  The brightness detection unit 19 includes a brightness sensor that detects the brightness around the video display device (the ambient illuminance). For example, a photodiode can be used as the brightness sensor. The detection result by the brightness detection unit is output to the light emission detection unit 12 and the area active control / luminance stretch unit 14.

  The mapping unit 13 generates tone mapping using the information on the light emission part detected by the light emission detection unit 12 and the Max luminance output from the area active control / luminance stretch unit 14, and applies it to the input video signal. To do. The Max luminance indicates the maximum luminance desired to be displayed on the screen and corresponds to the luminance stretch amount of the backlight.

The area active control / luminance stretch unit 14 divides the image based on the video signal into predetermined areas according to the input video signal, and extracts predetermined statistical values such as the maximum gradation value of the video signal for each divided area. Then, the lighting rate of the backlight unit 16 is calculated based on the maximum gradation value and the like. The lighting rate is determined for each area of the backlight unit 16 corresponding to the divided area of the video.
Moreover, the backlight part 16 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 16 is determined based on a predetermined arithmetic expression, but is basically maintained without reducing the luminance of the LED in an area having a bright maximum gradation value of high gradation. Then, an operation is performed to reduce the luminance of the LED in a dark area with low gradation.
Then, the area active control / luminance stretch unit 14 calculates the overall average lighting rate of the backlight unit 16 from the lighting rate of each region, and according to the average lighting rate, the area of the backlight unit 16 is calculated by a predetermined arithmetic expression. Calculate brightness stretch amount. As a result, the maximum luminance value (Max luminance) that can be taken in the area in the screen is obtained. With respect to the Max luminance obtained here, the Max luminance is adjusted based on the detection result of the brightness around the apparatus by the brightness detection unit 19 and is output to the mapping unit 13 of the signal processing unit 11.

  Then, the area active control / luminance stretch unit 14 returns the Max luminance adjusted according to the detection result of the surrounding brightness to the signal processing unit 11 to reduce the luminance corresponding to the luminance stretch of the backlight unit 16. . At this time, the luminance stretch is applied to the entire backlight unit 16, and the luminance reduction due to the video signal processing is performed on the portion regarded as not emitting light except the light emitting unit. As a result, the screen brightness of only the light emitting portion can be increased, video can be expressed with high contrast, and the image quality can be improved.

The area active control / luminance stretch unit 14 outputs control data for controlling the backlight unit 16 to the backlight control unit 15, and the backlight control unit 15 selects the LEDs of the backlight unit 16 based on the data. The emission luminance is controlled for each divided area. Although the brightness | luminance of LED of the backlight part 16 is performed by PWM (Pulse Width Modulation) control, it can be controlled so that it may become a desired value by electric current control or these combination.
The area active control / luminance stretch unit 14 outputs control data for controlling the display unit 18 to the display control unit 17, and the display control unit 17 controls the display of the display unit 18 based on the data. . The display unit 18 is a liquid crystal panel that is illuminated by the LED of the backlight unit 16 and displays an image.

  In the present embodiment, the control unit of the present invention controls the backlight unit 16 and the display unit 18, and includes a signal processing unit 11, an area active control / luminance stretch unit 14, a backlight control unit 15, and The display control unit 17 corresponds.

  When the display device is configured as a television receiving device, the television receiving device has means for selecting and demodulating a broadcast signal received by an antenna, and decoding and generating a reproduction video signal. The signal is appropriately subjected to predetermined image processing and input as the input video signal of FIG. Thereby, the received broadcast signal can be displayed on the display unit 18. 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.
The area active control / luminance stretch unit 14 divides the video into a plurality of predetermined areas (areas), and controls the emission luminance of the LEDs corresponding to the divided areas for each area. 2 to 3 are diagrams for explaining the light emission region control processing in the area active control / luminance stretch unit 14. Area active control applied to the present embodiment divides an image into a plurality of predetermined areas (areas), and controls the light emission luminance of the LED corresponding to the divided areas for each area.

  Here, the area active control / luminance stretch unit 14 divides one frame of video into a plurality of predetermined areas based on the input video signal, and extracts the maximum gradation value of the video signal for each of the divided areas. To do. For example, an image as shown in FIG. 2A is divided into a plurality of predetermined areas. Here, the maximum gradation value of the video signal in each region is extracted. In another example, other statistical values such as the average gradation value of the video signal may be used instead of the maximum gradation value. Hereinafter, an example in which the maximum gradation value is extracted will be described.

  The area active control / luminance stretch unit 14 determines the lighting rate of the LED for each area according to the extracted maximum gradation value. FIG. 2B shows the lighting rate of the LEDs in each region at this time. In a bright portion where the gradation of the video signal is high, a bright display is performed by increasing the lighting rate of the LED. The process at this time will be described more specifically.

  An example of a state when the maximum gradation value of each divided region of one frame is extracted is shown in FIG. In FIG. 3, it is assumed that the screen of one frame is divided into eight regions (regions <1> to <8>) in order to simplify the description. FIG. 3A shows the lighting rate of each region (regions <1> to <8>), and FIG. 3B shows the lighting rate of each region and the average lighting rate of the entire screen. Here, the lighting rate of the backlight LED in each region is calculated from the maximum gradation value in each region. The lighting rate can be indicated by, for example, the LED drive duty. In this case, the lighting rate Max is 100%.

In determining the 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. As an example, when the gradation value of the video is represented by 8-bit data of 0-255, when the maximum gradation value is 128, the backlight is (1 / (255/128)) ^2.2 = 0. Reduce to 217 times (21.7%).
In the example of FIG. 3, the lighting rate of the backlight is determined in the range of 10 to 90% for each region. 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 lighting rate of each area is calculated according to the determined arithmetic expression.
Then, the backlight lighting rate for each region calculated from the maximum gradation value of the video signal is averaged to calculate the average lighting rate of the backlight in one frame. In this example, the average lighting rate is the level of the average lighting rate shown in FIG. The average lighting rate is an example of an index related to brightness according to the present invention.

  FIG. 4 is a diagram for explaining the average lighting rate determination process more specifically. As described above, in the determination of the 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. Here, the actual lighting rate of each region is determined so as to accurately display the gradation to be displayed and to make the LED duty as low as possible. Although it is desired to make the LED duty as low as possible in each area, it is necessary to display accurately without squashing the gradation to be displayed. Therefore, the LED duty that can display the maximum gradation in the area and lower the LED duty as much as possible. (Temporary lighting rate) is set, and based on this, the gradation of the display unit 18 (here, the LCD panel) is set.

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 region in FIG. 3A are shown in FIG. The case indicated by will be described. Here, it is assumed that nine pixels correspond to one region. In the pixel group shown in FIG. 4A, the maximum gradation value is 128. In this case, as shown in FIG. 4B, the lighting rate of the backlight in that region is (1 / (255/128). )) ^2.2 = 0.217 times (21.7%).

  As an example, the area active control / luminance stretch unit 14 determines the lighting rate in this way, and calculates the gradation value for each pixel in the display unit 18 in consideration of the lighting rate for the region including the pixel. . 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.

The actual luminance of the backlight unit 16 is further stretched and enhanced based on the value of the Max luminance determined according to the average lighting rate. The original reference luminance is, for example, such luminance that the screen luminance is 550 (cd / m ² ) at the maximum gradation value. The reference luminance can be appropriately determined without being limited to this example.

FIG. 5 is a diagram for explaining a processing example of the area active control / luminance stretch unit 14. As described above, the area active control / luminance stretch unit 14 calculates the average lighting rate of the entire screen from the lighting rate determined according to the maximum gradation value of each region. The average lighting rate of the entire screen increases as the number of areas with high lighting rates increases. Then, the maximum luminance value (Max luminance) that can be taken is determined based on the relationship shown in FIG. The horizontal axis represents the backlight lighting rate (window size), and the vertical axis represents the screen luminance (cd / m ² ) at the Max luminance. The average lighting rate can be expressed as a ratio between a lighting region (window region) with a lighting rate of 100% and a light-off region with a lighting rate of 0%. The lighting rate is zero when there is no lighting region, the lighting rate increases as the window of the lighting region increases, and the lighting rate becomes 100% with full lighting.

In FIG. 5, the Max luminance when the backlight is fully lit (average lighting rate 100%) is, for example, 550 (cd / m ² ). Then, the Max luminance is increased as the average lighting rate decreases. At this time, a pixel having a gradation value of 255 gradations (in the case of 8-bit representation) has the highest screen brightness in the screen, and the maximum possible screen brightness (Max brightness). Therefore, 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.

When the average lighting rate is Q1, the value of Max luminance is the largest, and the maximum screen luminance at this time is 1500 (cd / m ² ). That is, at Q1, the maximum possible screen brightness is stretched to 1500 (cd / m ² ) compared to 550 (cd / m ² ) when all the lights are on. Q1 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.

From the average lighting rate Q1 with the maximum Max luminance to the average lighting rate 0 (all black), the value of Max luminance is gradually decreased. In the predetermined area where the average lighting rate is the lowest, the screen brightness is further reduced from 550 (cd / m ² ) at the time of full lighting. In other words, the screen brightness is stretched to a negative value when the entire lighting is used as a reference. The range where the average lighting rate is low corresponds to the image of a dark screen. Rather than stretching the backlight brightness to increase the screen brightness, the backlight brightness is reduced to improve the contrast. Reduce black float and maintain display quality.

  The area active control / luminance stretch unit 14 stretches the luminance of the backlight according to the curve of FIG. 5 and outputs the control signal to the backlight control unit 15. 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 14 is applied with tone mapping generated by signal processing performed by the signal processing unit 11 described below, and the low gradation region is gain-down and input. As a result, the luminance of the backlight is stretched in the low gradation non-light emitting area, and the luminance is reduced by the video signal processing. As a result, the screen luminance is enhanced only in the light emitting area, and the brightness is increased. It has become.

  The area active control / luminance stretch unit 14 outputs the average lighting rate of the backlight and the Max luminance value obtained from the detection result of the brightness detection unit 19 to the mapping unit 13 of the signal processing unit 11 according to the curve of FIG. . The mapping unit 13 performs tone mapping using the Max luminance output from the area active control / luminance stretch unit 14.

The signal processing unit 11 will be described.
The light emission detection unit 12 of the signal processing unit 11 detects a light emitting part from the video signal. FIG. 6 shows an example of a Y histogram generated from the luminance signal Y. The light emission detector 12 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. The luminance Y is one of the feature quantities of the video for creating the histogram, and other examples of the feature quantities will be described later. Here, it is assumed that a light emitting portion is detected for luminance Y.
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 is
Th2 = Ave + Nσ Expression (1)
And N is a predetermined constant.

The first threshold Th1 is set to suppress a sense of incongruity such as gradation in an area smaller than Th2.
Th1 = Ave + Mσ Expression (2)
And M is a predetermined constant, and M <N. Further, the value of M changes according to the detection result of ambient brightness by the brightness detection unit 19.
The values of the first and second threshold values Th1 and Th2 detected by the light emission detection unit 12 are output to the mapping unit 13 and used to generate tone mapping.

  FIG. 7 is a diagram illustrating an example of tone mapping generated by the mapping unit 13. The horizontal axis is the input gradation of the luminance value of the video, and the vertical axis is the output gradation. The pixels detected by the light emission detector 12 that are equal to or greater than the second threshold Th2 are portions that emit light in the video, and the gain is reduced by applying a compression gain except for the portions that emit light. 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 12 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 13 receives the Max luminance value from the area active control / luminance stretch unit 14. As described above, the Max luminance indicates the maximum luminance determined from the average lighting rate of the backlight and the detection result of the ambient brightness by the brightness detection unit 19, and is input, for example, as the value of the backlight duty. The

The first gain G1 is applied to a region smaller than the first threshold Th1,
G1 = (Ls / Lm) ^{1 / γ} Expression (3)
Is set by Ls is reference luminance (reference luminance when the backlight luminance is not stretched; for example, luminance when the maximum screen luminance is 550 cd / m ² ), and Lm is output from the area active control / luminance stretching unit 14 Max luminance. 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 means
G2 = (Th2-G1 · Th1) / (Th2-Th1) (4)
To determine the second gain G2.
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 13 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 14.

FIG. 8 is a diagram for explaining the Max luminance output by the area active control / luminance stretch unit 14.
The area active control / luminance stretch unit 14 receives the video signal to which the tone mapping generated by the mapping unit 13 is applied, performs area active control based on the video signal, and determines Max luminance based on the average lighting rate. . At this time, the Max luminance control curve changes according to the ambient brightness detection result from the brightness detection unit 19, but brightness detection is not considered here for the sake of explanation.

  The frame determined based on the above average lighting rate is N frame. The value of the Max luminance of the N frame is output to the mapping unit 13 of the signal processing unit 11. The mapping unit 13 generates tone mapping as shown in FIG. 7 using the inputted Max luminance of the N frame and applies it to the video signal of the N + 1 frame.

  Thus, Max luminance based on the area active average lighting rate is fed back and used for tone mapping of the next frame. The mapping unit 13 applies a gain (first gain G1) for reducing the video output for an area smaller than the first threshold Th1, based on the Max luminance determined in N frames. 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.

  Since a gain for reducing the video output in N frames is applied, in a region with a high lighting rate with an average lighting rate of Q1 or more, in N + 1 frames, the maximum gradation value for each region is lowered and the lighting rate is lowered. As a result, Max luminance tends to increase in N + 1 frames. As a result, 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 Q1, and the opposite tendency.

  Next, the detection process of the brightness detection unit 19 of the signal processing unit 11 will be described. In the embodiment according to the present invention, the Max luminance control curve corresponding to the average lighting rate as shown in FIG. 5 is changed according to the ambient brightness detection result in the brightness detection unit 19.

(Example of backlight brightness control based on brightness detection)
As described above, the area active control / luminance stretch unit 14 inputs the video signal to which the tone mapping generated by the mapping unit 13 is applied, performs area active control based on the video signal, and based on the average lighting rate Max brightness is determined. At this time, the area active control / luminance stretch unit 14 varies the Max luminance control curve according to the detection result of the ambient brightness in the brightness detection unit 19, and the average lighting rate increases as the ambient becomes darker. The curve is such that the screen brightness is lowered in a predetermined region where the brightness is low, or the relation between the average lighting rate and the Max brightness is made a gentle curve so that the entire Max brightness is lowered.
At the same time, the mapping unit 13 shifts the first threshold Th1 to a higher feature amount such as luminance when the surroundings are dark according to the surrounding brightness detection result in the brightness detecting unit 19, As a result, the tone of the dark area is lowered further by the video signal processing so that a contrast feeling can be obtained.

FIG. 9 is a diagram for explaining a control example of Max luminance that is changed according to the detection result of ambient brightness.
As described above, the area active control / luminance stretch unit 14 calculates the average lighting rate of the entire screen from the lighting rate determined according to the maximum gradation value of each region. The average lighting rate of the entire screen increases as the number of areas with high lighting rates increases. Then, the maximum luminance value (Max luminance) that can be taken is determined based on the relationship shown in FIG.

  At this time, the control curve that defines the relationship between the Max luminance and the average lighting rate in FIG. 9 is changed according to the detection result of the ambient brightness by the brightness detection unit 19. For example, as shown in FIG. 9, two levels of Max luminance control curves are prepared. When the surrounding brightness is bright, the control curve R1 is used, and when the surrounding brightness is dark, the control curve R2 is used. In the bright and dark cases, a predetermined threshold is set for the signal indicating the brightness detection result, and the detection result is compared with the threshold to determine whether the surrounding is brighter or darker than the predetermined level. For example, when ambient illuminance (lux) is detected by a brightness sensor using a photodiode, a threshold value of illuminance is set in advance, and it is determined whether the environment is bright or dark according to the ambient illuminance based on the detection result. Further, threshold values may be provided in multiple stages, and control may be performed according to the multi-stage ambient illuminance.

In the control curve of FIG. 9, the maximum Max luminance level in the entire range of the average lighting rate is B, the Max luminance level is C when the average lighting rate is 100%, and the average lighting rate having the maximum Max luminance is D. To do. In the control curve R1 in the case where the surroundings are bright, in this case, B is set to about 1500 cd / m ² , C is set to about 550 cd / m ² , and B is set to a luminance difference about 3 times C. In the control curve R1, even in a dark image area with a low average lighting rate, the Max luminance is set to be high to some extent to provide an image that looks bright in a bright ambient environment. Even if the average lighting rate is 0%, the Max luminance at this time is 550 cd / m ² .

On the other hand, in the control curve R2 when the surroundings are dark, the Max luminance is lowered in the dark image area where the average lighting rate is low within a predetermined range, compared to the control curve R1 in the bright surrounding environment. In this case, the Max luminance at the lowest lighting rate (lighting rate 0%) is 0 (cd / m ² ), and at this time, the backlight is completely turned off. In other words, if the C level of 550 cd / m ² is used as a reference, the backlight is stretched negatively in a predetermined region with a low lighting rate.

  In the dark curve area, the control curve R2 emphasizes preventing glare in a dark surrounding environment rather than increasing the Max luminance and enhancing the screen brightness. Further, in a dark video area, when the Max luminance is increased and the luminance stretch is performed, the feeling of black floating becomes conspicuous. Therefore, the Max luminance is suppressed to be low so that the black floating is not conspicuous. In this example, the position of the average lighting rate B having the Max luminance is maintained without being changed depending on the ambient brightness.

  In the example of FIG. 9, the control curve is set to two stages, but the control curve is not limited to two stages, and control can be performed in a plurality of stages including three or more stages. Further, the control curve may be generated each time so as to change steplessly according to the surrounding brightness (ambient illuminance) detected by the brightness detecting unit 19.

  FIG. 10 is a diagram for explaining another example of the control example of the Max luminance that is changed according to the detection result of the surrounding brightness. In the example of FIG. 10, the control curve that defines the relationship between the Max luminance and the average lighting rate is changed according to the detection result of the ambient brightness by the brightness detection unit 19 as in the example of FIG. The setting is different from the control curve. In the example of FIG. 10, two levels of Max luminance control curves are prepared. When the surrounding brightness is bright, control is performed with the control curve R3, and when the surrounding brightness is dark, control is performed with the control curve R4. In the case of light and dark, a predetermined threshold is set for a signal indicating the detection result in the same manner as described above, and the detection result is compared with the threshold to determine whether the surrounding is brighter or darker than the predetermined level. .

In the control curve R3 when the surroundings are bright, B is set to about 1500 cd / m ² , C is set to about 550 cd / m ² , and B is set to a brightness difference that is about three times that of C. Further, in a dark video region where the average lighting rate is low, the Max luminance is set lower than the C level during full lighting, and when the average lighting rate is 0%, the Max luminance is 0 (cd / m ² ). At this time, the backlight is completely turned off.
As a result, in the control curve R3 when the surroundings are bright, the brightness is increased by the brightness stretch due to the high Max brightness, and the brightness is reduced by the video signal processing in the area other than the light emitting part, so that the quality with high contrast is high. Video expression is possible. Also, in a dark region where the average lighting rate is close to the lowest, Max luminance is reduced to reduce the darkness of dark images.

On the other hand, in the control curve R4 when the surroundings are dark, the entire control curve is set to be gentler than the control curve R3, and the Max luminance is set to be lower than the entire control curve R3. In this case, the maximum Max luminance level B is suppressed to about 550 cd / m ² in R4 as compared to about 1500 cd / m ^{2 in} R3. In an environment where the surroundings are dark, glare is suppressed by setting Max brightness to a low value. Further, in an area where the average lighting rate is low and the image is dark, the Max luminance is further lowered than the control curve R3. In a dark ambient environment, the feeling of black floating on the screen due to luminance stretching becomes more conspicuous, so the Max luminance is kept low to prevent black floating. In this example, the position of the average lighting rate D having the Max luminance is maintained without being changed by the ambient brightness.

In the example of FIG. 10, the control curve is set in two stages, but the control curve is not limited to two stages, and control can be performed in a plurality of stages including three or more stages. Further, the control curve may be generated each time so as to change steplessly according to the ambient brightness.
For example, as a setting example when setting the control curve in three stages, when ambient illuminance is 400 lux, level B is 1500 cd / m ² , level C is 550 cd / m ^2, and ambient illuminance is 200 lux. the level B 900 cd / ^{m 2,} the level C and 300 cd / ^{m 2,} when the ambient illuminance is 500 lux, 450 cd / ^{m 2} level B, and level C can be set such that a 150 cd / ^{m 2.} In this case, the ratio of level B to level C is set to about 1.5 to 3 times, and the Max luminance is reduced along with the decrease in ambient illuminance even when the total lighting rate is 100%.

  FIG. 11 is a diagram for explaining still another example of the control example of the Max luminance that is changed according to the detection result of the surrounding brightness. In the example of FIG. 11, similarly to the example of FIG. 10, the control curve that defines the relationship between the Max luminance and the average lighting rate is changed in accordance with the detection result of the ambient brightness by the brightness detection unit 19. Here, the control curve for the Max luminance is prepared in two stages. When the surrounding brightness is bright, the control curve R5 is used for control. When the surrounding brightness is dark, the control curve R6 is used for control. In the case of light and dark, a predetermined threshold is set for a signal indicating the detection result in the same manner as described above, and the detection result is compared with the threshold to determine whether the surrounding is brighter or darker than the predetermined level. .

In the control curve R5 when the surroundings are bright, B is set to about 1500 cd / m ² , C is set to about 550 cd / m ² , and B is set to a luminance difference about 3 times C. Further, in a dark video region where the average lighting rate is low, the Max luminance is set lower than the C level during full lighting, and when the average lighting rate is 0%, the Max luminance is 0 (cd / m ² ). At this time, the backlight is completely turned off.
As a result, in the control curve R3 when the surroundings are bright, the brightness is increased by the brightness stretch due to the high Max brightness, and the brightness is reduced by the video signal processing in the area other than the light emitting part, so that the quality with high contrast is high. Video expression is possible. Also, in a dark region where the average lighting rate is close to the lowest, Max luminance is reduced to reduce the darkness of dark images.

On the other hand, in the control curve R6 when the surroundings are dark, the entire control curve is set to be gentler than the control curve R5, and the Max luminance is set to be lower than the entire control curve R5. In this case, the level B of the maximum of the Max luminance, versus about 1500 cd / ^{m 2} of R5, is reduced to about 550 cd / ^{m 2} in R6.
In the control curve 6, in an environment where the surroundings are dark, the feeling of glare is suppressed by setting the Max luminance lower. Further, in an area where the average lighting rate is low and the image is dark, the Max brightness is further lowered than the control curve R5, and the Max brightness is kept low so that the black floating is not noticeable.
In the control curve R6, the position D of the average lighting rate having the Max luminance is shifted to the low average lighting rate side with respect to the control curve R5. As a result, it is possible to reproduce with emphasis on a relatively small area of a brilliant portion of the entire dark image.

  In the example of FIG. 11, the control curve is set in two stages, but the control curve is not limited to two stages, and control can be performed in a plurality of stages including three or more stages. Further, the control curve may be generated each time so as to change steplessly according to the ambient brightness.

  FIG. 12 is a diagram illustrating the first threshold value that is changed according to the detection result of ambient brightness. As described above, the light emission detection unit 12 generates a Y histogram by integrating the number of pixels for each luminance gradation 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 a second threshold value Th2 for defining a light emission boundary and a first threshold value for suppressing a sense of incongruity such as gradation in an area smaller than Th2. Th1 (Th1 = Ave + Mσ) is set.

  At this time, the position of the first threshold Th1 in FIG. 12 is changed according to the detection result of the surrounding brightness by the brightness detecting unit 19. Specifically, the value of “M” of Th1 = Ave + Mσ is changed to change the position of Th1 in the luminance direction of the histogram. At this time, the position of the first threshold Th1 may be set in advance in a plurality of stages according to the detection result of the brightness detection unit 19, or may be changed in a stepless manner according to the brightness detection result. The position of the first threshold Th1 may be set.

  For example, as shown in FIG. 12, as the brightness detected by the brightness detection unit 19 becomes darker, the value of M is increased and the first threshold Th1 is shifted to the higher luminance side. As a result, in an environment where the surroundings are dark, the position of the first threshold Th1 is shifted to the high luminance side to emphasize the sharpness of the image quality in the dark environment, so that the image quality emphasizes the contrast. On the other hand, in an environment where the surroundings are bright, the first threshold value Th1 is maintained on the low luminance side so that the image quality emphasizes the brightness of the screen.

  FIG. 13 is a diagram illustrating an example of tone mapping according to brightness detection. As described above, the mapping unit 13 sets the first gain G1 for an area smaller than the first threshold Th1, and sets the second gain G2 so as to linearly connect Th1 and Th2, thereby toning the tone. Perform mapping. At this time, tone mapping is performed according to the position of the first threshold Th1 determined according to the result of detecting ambient brightness by the brightness detection unit 19. In this case, as shown in FIG. 12, as the surrounding brightness becomes darker, the first threshold value Th1 shifts to the high luminance side, thereby suppressing the gradation of the low luminance region in a wider range, It is possible to obtain an image quality that emphasizes a sense of contrast.

FIG. 14 is a diagram illustrating a state in which the screen brightness is enhanced by the processing of the area active control / luminance stretch unit 14. The horizontal axis is the gradation value of the input video signal, and the vertical axis is the screen brightness (cd / m ² ) of the display unit 18.
T2 and T3 correspond to the positions of the gradation values of the first and second threshold values Th1 and Th2 used in the light emission detection unit 12, respectively. As described above, the signal processing for reducing the output gradation of the video signal according to the luminance stretch amount of the backlight is not performed in the region of the second threshold Th2 or more detected by the light emission detection unit 12. As a result, in T3 to T4, the input video signal is enhanced and displayed with a γ curve according to the Max luminance determined by the area active control. For example, if the Max luminance is 1500 (cd / m ² ), the screen luminance is 1500 (cd / m ² ) when the input video signal has the highest gradation value (255). The Max luminance in this case is the Max luminance determined according to the average lighting rate determined based on the video signal and the surrounding brightness detection result by the brightness detection processing.

  On the other hand, in the case of input gradation values from T1 to T2, 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 T2) 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 14. From T2 to T3, the screen luminance changes according to the tone mapping of Th2 to Th1.

When the Max luminance increases, the difference in the screen luminance direction between the curve based on the reference luminance of T1 to T2 and the curve based on the Max luminance of T3 to T4 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 14.

In this way, when the input video signal is between 0 gradation (T1) and T2, 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 contrast will decrease and the quality of the product such as black floating will decrease. Try not to go up.
In addition, since the range where the input video signal is greater than or equal to T3 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.

  In this case, for example, when the surrounding brightness becomes dark due to the detection result by the brightness detection unit 19 and the Max luminance is suppressed, a curve based on the reference luminance of T1 to T2 and a curve based on the Max luminance of T3 to T4 The difference in the screen brightness direction is reduced. That is, as the Max luminance determined according to the amount of ambient brightness detected by the brightness detection unit decreases, the curve from T3 to T4 shifts to the low luminance side. Further, since the position of T2 corresponds to the position of the first threshold th1 that changes according to the detection result of the surrounding brightness, when the surrounding becomes dark, the position of T2 also shifts to the high gradation side of the input signal, and the contrast The display is focused on feeling. The γ curves from T1 to T2 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 that gives a difference from the enhancement region of the light emitting portion. .

(Embodiment 2)
FIG. 15 is a diagram for explaining another embodiment of the video display device according to the present invention.
The second embodiment has the same configuration as that of the first embodiment, but unlike the first embodiment, the value of the Max luminance used when performing tone mapping is changed to an area active control / luminance stretch unit. The luminance stretch amount is determined based on the detection results of the light emission detection unit 12 and the brightness detection unit 19 without being determined in 14, and tone mapping is executed based on the determined luminance stretch amount. Therefore, the mapping unit 13 of the signal processing unit 11 does not need to output the Max luminance value by luminance stretching from the area active control / luminance stretching unit 14 as in the first embodiment.

  Similar to the first embodiment, the brightness detection unit 19 includes a brightness sensor such as a photodiode that detects the ambient brightness (ambient illuminance) of the video display device, and the detection result of the brightness detection unit. Is output to the light emission detector 12.

  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 12 uses the luminance as the video feature amount, and generates a Y histogram by integrating the number of pixels for each luminance gradation of each pixel 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. As the feature amount of the video, other feature amounts described later can be used, but here, luminance is used.

In the present embodiment, in addition to the first threshold Th1 and the second threshold Th2 of 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.
Therefore,
Th3 = Ave + Qσ (M <Q ≦ N) (5)
It becomes.

式（６）において、count[i]は、階調値ｉについての画素数のカウントである。また、ｉ²−（Thresh3）²は、図２０で示したような輝度についての距離（輝度の差）を指し、代わりに、明度Ｌ^*における閾値からの距離を採用してもよい。なお、この２乗は輝度を表すものであり、実際には２．２乗となる。つまり、デジタルのコード値がｉの場合、輝度はｉ^2.2となる。そのとき、明度Ｌ^*は（ｉ^2.2）^1/3≒ｉとなる。実際の映像表示装置で検証した結果、輝度での閾値からの差が明度での閾値からの差などより効果的であった。
また、式（６）において、全画素数とはｉ＞Ｔｈ３に限らず全ての画素数をカウントした値を指す。スコアとしてこのような計算値を採用すると、発光部分のうちＴｈ３から離れた高階調の画素が多い場合にはスコアが高くなる。また、Ｔｈ３以上の画素数が一定であっても、階調が高い画素が多い方がスコアは高くなる。第３の閾値Ｔｈ３以上の階調値を持つ画素の画素数をカウントし、閾値Ｔｈ３からの距離に重み付けをして算出することにより明るさの度合いを示すもので、例えば、
スコア＝１０００×Σｃｏｕｎｔ［ｉ］×（ｉ^２−Ｔｈ３^２）／（Σｃｏｕｎｔ［ｉ］
×Ｔｈ３^２） ・・・式（６）
によって計算される。Σｃｏｕｎｔ［ｉ］は、階調値ｉごとに画素数をカウントして積算したものである。従って、発光部分のうちＴｈ３から離れた高階調の画素が多い場合にはスコアが高くなる。また、Ｔｈ３以上の画素数が一定であっても、階調が高い画素が多い方がスコアは高くなる。 FIG. 17 is a diagram illustrating a calculation example of the luminance stretch amount according to the pixel equal to or greater than the third threshold Th3. 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 corresponds to an example of an index related to the brightness of the present invention.
The score is defined as [ratio of pixels greater than or equal to a certain threshold value] × [distance from threshold value (brightness difference)], and counts the number of pixels having gradation values larger than the third threshold value Th3. The degree of brightness is shown by weighting and calculating the distance from, and is calculated by the following equation (6), for example.

In equation (6), count [i] is a count of the number of pixels for the gradation value i. Further, i ² − (Thresh3) ² indicates the distance (brightness difference) with respect to the luminance as shown in FIG. 20, 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 Expression (6), the total number of pixels refers to a value obtained by counting all the numbers of pixels without being limited to i> Th3. 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 equal to or greater than Th3 is constant, the score increases as the number of pixels with high gradation increases. It shows the degree of brightness by counting the number of pixels having gradation values equal to or greater than the third threshold Th3 and calculating the weighted distance from the threshold Th3.
Score = 1000 × Σcount [i] × (i ² −Th3 ² ) / (Σcount [i]
× Th3 ² ) (6)
Calculated by Σcount [i] is obtained by counting and integrating the number of pixels for each gradation value i. Therefore, the score is high when there are many high gradation pixels far from Th3 in the light emitting portion. Even if the number of pixels equal to or greater than Th3 is constant, the score increases as the number of pixels with high gradation increases.

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 brightness. In this example, in a portion where the score is higher than a certain level, the maximum screen luminance that can be obtained after luminance stretching is set to 1500 (cd / m ² ). When the score is low, the luminance stretch amount is set to be smaller as the score is smaller. Then, the light emission detection unit 12 changes the control curve that defines the relationship between the score and the luminance stretch amount according to the detection result of the ambient brightness in the brightness detection unit 19. This luminance stretch amount is the same concept as the Max luminance of the first embodiment, and is indicated by, for example, a backlight duty value.

  FIG. 18 is a diagram for explaining a setting example of a control curve for the luminance stretch amount that is changed according to the detection result of the surrounding brightness. As described above, the light emission detection unit 12 determines the luminance stretch amount according to the score of the pixel value equal to or greater than the threshold Th3. The brightness detection unit determines a control curve that defines the relationship between the score and the luminance stretch amount at this time. The ambient brightness output from 19 is changed in accordance with the detection result.

  For example, as shown in FIG. 18, two steps of brightness stretch control curves are prepared. When the surrounding brightness is bright, the control curve U1 is used. When the surrounding brightness is dark, the control curve U2 is used. To control. In the bright and dark cases, a predetermined threshold is set for the signal indicating the brightness detection result, and the detection result is compared with the threshold to determine whether the surrounding is brighter or darker than the predetermined level. For example, when ambient illuminance (lux) is detected by a brightness sensor using a photodiode, a threshold value of illuminance is set in advance, and it is determined whether the environment is bright or dark according to the ambient illuminance based on the detection result.

In the control curve of FIG. 18, the level of the maximum luminance stretch amount in the entire range of the score is E, the level of the minimum luminance stretch amount in the entire range of the score is F, and the level E of the maximum luminance stretch amount as the score decreases. Let I be the score at which the luminance stretch amount starts to decrease. In the example of FIG. 18, in the control curve U1 when the surrounding brightness is bright, E is about 1500 cd / m ² and F is 500 cd / cm ² , but in the control curve U2 when the surrounding brightness is dark, , E are reduced to about 900 cd / m ² and F is reduced to 300 cd / m ² . Thus, the ratio of the level E to the level F is set to about 1.5 to 3 times, and the entire control curve is lowered to the low luminance stretch amount side as the ambient illuminance is reduced.

  With the control described above, the control curve U1 when the surroundings are bright increases the shine feeling by the high luminance stretch amount, and the luminance is reduced by the video signal processing in the area other than the light emitting portion, so that the quality with a high contrast feeling is obtained. High video expression is possible. Further, in the case of a dark image with the lowest score, the brightness stretch amount is reduced to reduce the darkness of dark images.

  On the other hand, in the control curve U2 in the case where the surroundings are dark, the feeling of glare is suppressed by setting the luminance stretch amount low. Further, in a region where the score is low and the video is dark, the luminance stretch amount is further reduced as compared with the control curve U1. In a dark surrounding environment, the feeling of black floating on the screen due to luminance stretch becomes more conspicuous, so the amount of luminance stretch is further reduced so that black floating does not stand out. In this example, the point I at which the level of the luminance stretch amount changes is maintained without being changed depending on the ambient brightness.

  In the example of FIG. 18, the control curve is set in two stages, but the control curve is not limited to two stages and can be controlled in a plurality of stages including three or more stages. Moreover, you may make it produce | generate a control curve each time so that it may change without a step according to it. When threshold values are provided in multiple stages and controlled in multiple stages according to ambient illuminance, the control curve is changed in stages in the direction of the control curves U1 to U2 as the ambient brightness becomes darker.

FIG. 19 is a diagram for explaining another setting example of the control curve of the luminance stretch amount to be changed according to the detection result of the surrounding brightness. In the example of FIG. 19, the control curve that defines the relationship between the score and the luminance stretch amount is changed according to the detection result of the surrounding brightness by the brightness detecting unit 19 as in the example of FIG.
Here, two steps of brightness stretch control curves are prepared. When the surrounding brightness is bright, the control curve U3 is used. When the surrounding brightness is dark, the control curve U4 is used. In the case of light and dark, a predetermined threshold is set for a signal indicating the detection result in the same manner as described above, and the detection result is compared with the threshold to determine whether the surrounding is brighter or darker than the predetermined level. .

In the example of FIG. 19, as in the example of FIG. 18, the surrounding brightness becomes dark, so the entire control curve is reduced from U3 to U4. However, unlike the example of FIG. The position of I is also changed. That is, in the control curve U4 where the surrounding brightness is dark, the position of the point I is shifted to the high score side as compared with the control curve U3 where the surrounding brightness is bright. Thus, when the surroundings are dark, even a bright video with a high score to some extent, the luminance stretch amount is suppressed to prevent a dazzling feeling.
In the example of FIG. 19, the control curve is set in two stages, but the control curve is not limited to two stages, and control can be performed in a plurality of stages including three or more stages. Further, the control curve may be generated each time so as to change steplessly according to the ambient brightness.

  Next, the light emission detection unit 12 changes the position of the first threshold Th1 in the Y histogram according to the detection result of the brightness detection unit 19 by the same processing as in the first embodiment. For example, as described in the first embodiment, as the brightness detected by the brightness detection unit 19 becomes darker, the value of M is increased and the first threshold Th1 is shifted to the higher luminance side. As a result, in an environment where the surroundings are dark, the position of the first threshold Th1 is shifted to the high luminance side to emphasize the sharpness of the image quality in the dark environment, so that the image quality emphasizes the contrast. On the other hand, in an environment where the surroundings are bright, the first threshold value Th1 is maintained on the low luminance side so that image quality is achieved with emphasis on screen brightness.

The luminance stretch amount determined according to the values of the first and second threshold values Th1 and Th2 output from the light emission detection unit 12 and the score of the pixel equal to or greater than Th3 is output to the mapping unit 13 and used for generation of tone mapping. Is done.
The toe mapping process in the mapping unit 13 is the same as in the first embodiment. That is, as shown in FIG. 13, the first gain G1 is set for an area smaller than the first threshold Th1 set by the light emission detector 12, and the second gain is set so as to linearly connect Th1 and Th2. Set the gain G2. At this time, when setting the gain G1, the luminance stretch amount determined according to the detection result of the surrounding brightness by the brightness detection unit 19 is used, and the luminance is obtained by video signal processing according to the luminance stretch amount of the backlight. Reduce. In this case, as shown in FIG. 12, as the surrounding brightness becomes darker, the first threshold value Th1 is shifted to the higher luminance side, and thereby, the gradation of the low luminance region can be suppressed to be lower in a wider range. Therefore, it is possible to obtain an image quality with more emphasis on contrast. The obtained tone mapping is applied to the input video signal and input to the area active control / luminance stretch unit 14.

  The processing in the area active control / luminance stretch unit 14 is the same as in the first embodiment. However, the area active control / luminance stretch unit 14 does not need to determine the Max luminance from the average lighting rate of the backlight and output it to the signal processing unit 11 as in the first embodiment, and conversely, the light emission of the signal processing unit 11 Based on the luminance stretch amount output from the detection unit 12, the luminance of the LED of the backlight unit 16 is stretched.

  That is, the area active control / luminance stretch unit 14 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 luminance stretch amount output from the light emission detection unit 12, 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 quality image is displayed be able to. The relationship between the input video signal and the screen brightness is the same as that in FIG. 14 shown in the first embodiment.

(Embodiment 3)
FIG. 20 is a view for explaining still another embodiment of the video display apparatus according to the present invention.
The third embodiment has the same configuration as the second embodiment and performs the same operation as the second embodiment. However, unlike the second embodiment, the luminance stretch unit 20 performs area active control. Without performing, the luminance of the backlight unit 16 is stretched based on the luminance stretch amount output from the light emission detection unit 12 of the signal processing unit 11.

  That is, the luminance stretch unit 20 inputs the video signal to which the tone mapping generated by the mapping unit 13 is applied, and outputs control data for displaying the video signal to the display control unit 17. At this time, processing by area active control is not performed. On the other hand, the entire backlight unit 16 is stretched uniformly based on the luminance stretch amount output from the light emission detection unit 12.

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.
Since the operation of the other components in the third embodiment is the same as that of the second embodiment, repeated description is omitted.

(Other features)
In each of the above examples, the luminance Y is used as the feature amount of the light emission unit detection processing in the light emission detection unit 12, a luminance histogram is generated, and the light emission unit is detected therefrom. As a feature value for generating a histogram, for example, CMI (Color Mode Index) or MaxRGB can be used in addition to luminance.

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
L * / L * modeboundary × 100 (7)
Defined by

  The 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 (7), L * is the brightness of the color of interest, and L * modeboundary is the brightness 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 brightest 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 J1 in FIG. Next, the chromaticity is calculated from the converted XYZ, and the 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. 21 is J2.

From these values, the CMI is calculated using the above equation (7). CMI is indicated by the ratio of L * of the target pixel and L * (L * modeboundary) of the brightest color of the chromaticity.
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.

  In another example, the feature amount is data (MaxRGB) 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. 22B, 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 (in this case R) is r1, and the gradation of the brightest color R is r2,
r1 / r2 × 100 (8)
A value similar to CMI can be obtained. 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.

  Then, a value is calculated according to the above equation (8) for each pixel to create a histogram. An average value Ave. and a standard deviation σ are calculated from this histogram, and each threshold value is set to detect a light emitting portion, or to detect a black amount. The histogram at this time may be obtained by integrating the RGB maximum gradation values of the pixels without converting them to values of 0 to 100 according to Equation (8).

DESCRIPTION OF SYMBOLS 11 ... Signal processing part, 12 ... Light emission detection part, 13 ... Mapping part, 14 ... Area active control / luminance stretch part, 15 ... Backlight control part, 16 ... Backlight part, 17 ... Display control part, 18 ... Display part , 19 ... detection unit, 20 ... luminance stretch unit.

Claims (2)

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,
The control unit adjusts the luminance of the light source based on a control curve that defines a relationship between a brightness-related index calculated from the input video signal based on a predetermined condition and a luminance stretch amount for stretching the luminance of the light source. Stretch and increase,
Based on a predetermined feature amount of the input video signal, a light emitting unit that is regarded as a light emitting image is detected, and the luminance of the video signal of the non-light emitting unit excluding the light emitting unit is reduced, thereby the light emitting unit An image display device that enhances the display brightness of
The video display device has a brightness detection unit that detects the brightness around the video display device,
The video display device, wherein the control unit switches the control curve according to brightness around the video display device detected by the brightness detection unit.   A television receiver comprising the video display device according to claim 1.

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