JP4352755B2 - Video signal contrast processing circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a video signal contrast processing circuit that performs signal processing for improving the image quality of a video signal displayed in a so-called letterbox format with black bands at the top and bottom.
[0002]
[Prior art]
Conventionally, in a television (TV) receiver, as a function of enhancing the contrast of a displayed image, black level expansion is achieved by reducing the intermediate brightness when black level is detected and black is floating, thereby producing a tightened image. In addition, there are used dynamic contrast correction for detecting dark scenes to increase the contrast and improving the appearance, and methods for effectively using the dynamic range by detecting the APL level and adjusting the DC transmission rate.
[0003]
In addition, the applicant of the present invention prevents erroneous operation of the auto pedestal processing unit in an image display device configured to display a wide aspect ratio image and a standard aspect ratio image by display means of a wide aspect ratio display screen. In order to perform an image display that effectively uses the dynamic range of the means, an image display device is proposed in which an auto pedestal processing unit is operated during an effective display period of an aspect ratio converted video signal (for example, a patent Reference 1).
[0004]
[Patent Document 1]
Japanese Patent No. 3257788 [0005]
[Problems to be solved by the invention]
By the way, when a digital video / versatile disc (so-called DVD) in which a movie that has been spreading in recent years is played back, a very large number of so-called letter boxes are displayed with black bands on the top and bottom. . FIG. 3 shows an example of the letterbox display screen 110. The widths B1 and B2 of the black belt 115 on the letterbox display screen 110 vary depending on the recorded contents of the DVD, that is, the movie.
[0006]
Conventionally, if a video signal reproduced from a DVD is directly passed through a black level expansion circuit, a dynamic contrast correction circuit, and a DC transmission rate correction circuit, the correction will malfunction due to the upper and lower black bands. At present, functions such as the black level expansion processing, dynamic contrast correction, and DC transmission rate correction are turned off in order to detect the occurrence and prevent malfunction. In other words, there is a problem that black level expansion processing, dynamic contrast correction, and DC transmission rate correction for improving image quality cannot be applied in playback of a DVD movie that requires higher image quality display.
[0007]
Therefore, in view of the conventional situation as described above, an object of the present invention is to perform black level expansion processing for improving image quality, dynamic contrast correction, and DC transmission for an input video signal having various black band widths depending on the source. The purpose is to enable the rate correction to be applied effectively.
[0008]
[Means for Solving the Problems]
In the present invention, the black band width of the letterbox signal of the input signal having various black band widths is detected depending on the source, the effective period is defined, and black level expansion processing or dynamics is performed only during the effective period of the input signal. Enable functions such as contrast correction and DC transmission rate correction.
[0009]
That is, a contrast processing circuit for a video signal according to the present invention includes a measuring unit that measures an effective period of an input video signal, and an effective video region setting unit that sets an effective video region based on a measurement result by the measuring unit. Contrast processing means for adaptively performing contrast processing on the effective video area set by the effective video area setting means of the image displayed by the input video signal , and the contrast processing means includes the effective video area A DC transmission rate correction circuit that performs APL detection of only the effective video area set by the setting means, adaptively corrects the DC transmission rate of the luminance signal based on the APL detection result, and effectively uses the dynamic range; The effective video area setting means for the luminance signal whose DC transmission rate is adaptively corrected by the DC transmission rate correction circuit. Black level expansion is performed with black area detection and black level detection only in the set effective video area, and black level expansion processing that lowers the intermediate luminance according to the amount and area of black on the screen based on the detection results APL detection is performed only on the effective video area set by the effective video area setting means for the luminance signal that has been subjected to the black level expansion processing in the circuit and the black level expansion circuit, and the luminance signal is dark based on the APL detection result. It comprises a dynamic contrast correction circuit for performing a dynamic contrast correction process for detecting a scene and increasing the contrast .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0011]
The present invention is applied to, for example, a video display apparatus 100 configured as shown in the block diagram of FIG.
[0012]
The video display device 100 includes an analog tuner circuit 10 for receiving an analog television broadcast, and an analog television signal CVBS received via the analog tuner circuit 10 is digitally converted by an analog-digital (AD) converter 11. Then, the luminance signal Y1 and the chroma signal C1 are separated by the YC separation circuit 12, and further, the chroma decoder 13 decodes them into the component signals of the luminance signal Y1 and the color difference signals U1, V1.
[0013]
The video display device 100 also includes a digital tuner circuit 20 for receiving digital television broadcasts. The digital television signal TS received via the digital tuner circuit 20 is converted into a luminance signal Y2 by the MPEG decoder 21. The color difference signals U2 and V2 are decoded into component signals.
[0014]
Further, the video display device 100 includes a component video signal input terminal 30 so that component signals Y3, U3, V3 reproduced from, for example, a DVD are digitized by analog-digital (AD) converters 31, 32, 33. It has become.
[0015]
The video display device 100 includes component signals Y2, U2, and V2 decoded from the digital television signal TS by the MPEG decoder 21 and DVD component signals digitized by the analog-digital converters 31, 32, and 33. A first signal selection circuit 40 for selecting one of Y3, U3 and V3, and component television signals Y4, U4 and V4 selected by the first signal selection circuit 40 and the analog television decoded by the chroma decoder 13 A second signal selection circuit 50 that selects one of the component signals Y1, U1, and V1 of the signal CVBS is provided. The color difference signals U5, V5 of the component signals Y5, U5, and V5 selected by the second signal selection circuit 50 are provided. Is supplied to the COL / HUE processing circuit 60, and , The luminance signal Y5 is adapted to be supplied to the contrast processing circuit 70.
[0016]
The COL / HUE processing circuit 60 performs processing such as hue adjustment on the color difference signals U5, V5 of the component signals Y5, U5, V5 selected by the second signal selection circuit 50, and has processed the color difference signals U6, V6. Is supplied to the matrix circuit 90.
[0017]
Further, the contrast processing circuit 70 performs contrast processing on the luminance signals Y5 of the component signals Y5, U5, V5 selected by the second signal selection circuit 50, and the processed luminance signal Y6 is passed through the sharpness circuit 80. This is supplied to the matrix circuit 90.
[0018]
The matrix circuit 90 forms the three primary color signals R, G, and B from the component signals Y6, U6, and V6, and supplies the three primary color signals R, G, and B to the drive circuit of the display unit via an output circuit (not shown). Supply.
[0019]
The contrast processing circuit 70 in the video display apparatus 100 performs processing for improving the contrast feeling on the luminance signals Y5 of the component signals Y5, U5, and V5 selected by the second signal selection circuit 50. FIG. As shown in FIG. 5, the measurement circuit 71 that measures the effective period of the input luminance signal Y5, the effective video region setting circuit 72 that sets the effective video region based on the measurement result by the measurement circuit 71, and the input luminance signal Y5 A DC transmission rate correction circuit 73, a black level expansion circuit 74, and a dynamic contrast correction circuit 75 that adaptively perform contrast processing on the effective video area set by the effective video area setting circuit 72 of the image displayed by Prepare.
[0020]
The measurement circuit 71 measures horizontal and vertical effective area periods, a period from the synchronization signal to the video start period, and a period from the end of the video signal to the next synchronization signal. The measurement of the effective period is to detect a region having a value larger than a certain threshold level. As shown in the example of the letterbox display screen 110 in FIG. 3, in the case of a letterbox signal having black bands 115 above and below, the width B1 and B2 sections of the upper and lower black bands 115 are determined as invalid area periods, A section A in which an image signal exists is detected as an effective area period.
[0021]
Based on the period measured by the measurement circuit 71, the effective video area setting circuit 72 sets the effective video area A. In the case of a letterbox signal, since black bands 115 exist above and below, this area is detected, the inside of this area is determined as the effective video area A of the image, and the effective video area A is determined by setting the register. The mask pulse (MSK_MVP1) shown is generated.
[0022]
The mask pulse (MSK_MVP1) is supplied from the APL detection circuit 73A of the DC transmission rate correction circuit 73, the black area detection circuit 74A of the black level expansion circuit 74, the black level detection circuit 74B, and the APL detection circuit of the dynamic contrast correction circuit 75. 75A.
[0023]
In the DC transmission rate correction circuit 73, the APL detection circuit 73A performs APL detection only on the image effective area A in accordance with the mask pulse (MSK_MVP1), and changes the DC transmission rate of the luminance signal Y5 based on the APL detection result. I do. By the DC transmission rate correction in the DC transmission rate correction circuit 73, the APL level can be detected and the DC transmission rate of the luminance signal Y5 can be adjusted to effectively use the dynamic range.
[0024]
Further, in the black level expansion circuit 74, the black area detection circuit 74A and the black level detection circuit 74B perform black area detection and black level detection only in the image effective area A according to the mask pulse (MSK_MVP1), and detect these. Based on the result, black level expansion processing is performed on the luminance signal Y5. The black level expansion processing in the black level expansion circuit 74 can reduce the intermediate luminance in accordance with the amount and area of black on the screen and make the screen tight when black below a certain area exists. .
[0025]
Further, in the dynamic contrast correction circuit 75, the APL detection circuit 75A performs APL detection of only the image effective area A in accordance with the mask pulse (MSK_MVP1), and dynamic contrast correction processing is performed on the luminance signal Y5 based on the APL detection result. Apply. The dynamic contrast correction processing in the dynamic contrast correction circuit 75 can detect a dark scene and increase the contrast to improve the appearance.
[0026]
In the component signals Y3, U3, and V3 reproduced from the DVD input via the input terminal 30, the widths B1 and B2 of the black belt 115 on the letterbox display screen 110 vary depending on the recorded contents of the DVD, that is, the movie. In this contrast processing circuit 70, the effective period of the input video signal Y5 is measured by the measuring circuit 71, and the effective video area A is set by the effective video area setting circuit 72 based on the measurement result, thereby correcting the DC transmission rate. Or black level expansion or dynamic contrast correction can be applied only to the effective image area A.
[0027]
【The invention's effect】
As described above, according to the present invention, the positions of the upper and lower black bands in the letterbox signal are detected, and the APL detection for contrast correction and the black area and black level detection are masked in this portion to thereby detect the DVD movie signal. Even for letterbox signals like this, DC transmission rate correction, black level expansion and dynamic contrast correction can be corrected only in the area of the effective video signal, and you can enjoy a tight video signal with a sense of contrast. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of a video display device to which the present invention is applied.
FIG. 2 is a block diagram illustrating a configuration example of a contrast processing circuit in the video display device.
FIG. 3 is a diagram illustrating an example of a letterbox display screen.
[Explanation of symbols]
100 video display device, 10 analog tuner circuit, 11 analog-digital converter, 12 YC separation circuit, 13 chroma decoder, 20 digital tuner circuit, 21 MPEG decoder, 30 input terminal, 31, 32, 33 analog-digital converter, 40th 1 signal selection circuit, 50 second signal selection circuit, 60 COL / HUE processing circuit, 70 contrast processing circuit, 80 sharpness circuit, 90 matrix circuit, 71 measurement circuit, 72 effective video area setting circuit, 73 DC transmission rate correction Circuit, 74 black level expansion circuit, 75 dynamic contrast correction circuit, 110 display screen, 115 black belt

Claims (1)

A measuring means for measuring the effective period of the input video signal;
Effective video area setting means for setting an effective video area based on the measurement result by the measurement means;
Contrast processing means for adaptively performing contrast processing on the effective video area set by the effective video area setting means of the image displayed by the input video signal ,
The contrast processing means performs APL detection only on the effective video area set by the effective video area setting means, and adaptively corrects the DC transmission rate of the luminance signal based on the APL detection result, thereby adjusting the dynamic range. A black area is detected only in the effective video area set by the effective video area setting means for the DC transmission rate correction circuit to be effectively used and the luminance signal in which the DC transmission ratio is adaptively corrected by the DC transmission rate correction circuit. A black level expansion circuit that performs black level expansion processing that performs black level detection that lowers the intermediate luminance according to the amount and area of black on the screen based on the detection result, and black level expansion in the black level expansion circuit For the processed luminance signal, APL detection is performed only for the effective image area set by the effective image area setting means, and the APL detection result is obtained. Contrast processing circuit of a video signal consisting of dynamic contrast compensation circuit for performing dynamic contrast correction processing to increase the contrast by detecting dark scene based on.

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