JP2009198935A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve motion blur to display a moving image with high quality. <P>SOLUTION: A liquid crystal display is provided with; a face-detecting means; a brightness-determining means; an edge-detecting means; an image moving amount detecting means; a moving image line determining means which determines moving image lines according to the output of the moving amount detecting means; a moving image block identifying means which identifies consecutive moving image lines, as a moving image block, both from the output of the moving image line-determining means and from the output of the face-detecting means, and then determines whether a face image is included in the moving image block; and a PWM pulse-generating means which controls the blinking of a backlight in accordance with the output of the moving image block identifying means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to light source (backlight) control used in video equipment such as a liquid crystal television or projector having a light source such as a backlight.

  The CRT is an impulse-type display device in which nothing is displayed until the next display is performed after the phosphor is instantaneously illuminated for each field, and a moving image can be viewed as a smooth image without a feeling of afterimage. On the other hand, in a liquid crystal display device, display data is written once in one frame to pixels arranged in a matrix using data signal lines and scanning signal lines. The written display data is held for one frame period. In this way, a so-called hold-type display element that continues to display the same image for one frame displays an image at the correct position at a certain moment in one frame as a display, but actually at another time. An image at a location different from the position existing at the time is displayed. Since humans try to average those images, the images become blurred, and there is a problem that it is difficult to eliminate moving image blur regardless of the response speed of the liquid crystal.

  As a method for solving this problem, the following liquid crystal display device is used.

  FIG. 5 is a block diagram showing a configuration of a conventional liquid crystal display device (for example, described in Patent Document 1).

The conventional liquid crystal display device divides the display area of the liquid crystal panel 1 into a plurality of blocks with a plurality of adjacent scanning line groups as one block, and each block in the image of one vertical period input to the liquid crystal panel 101 is divided. The presence / absence of a moving image is detected by the comparison circuit 106, the comparison result storage circuit 107, and the BL waveform control circuit 108. The BL waveform control circuit 108 impulses the display by adjusting the waveform and phase of the driving voltage of the backlight 110 in one vertical period according to the appearance state of the moving image existence block in one vertical period, for example. When a moving image exists in a part of an image in one vertical period, the moving image in the moving image existence block can be displayed with high quality.
JP 2004-309592 A

  However, in the conventional configuration, when the entire screen is a moving image or when the moving image exists in a plurality of non-continuous blocks, the moving image cannot be displayed with high quality. Therefore, there is a problem that most moving images are not applicable and high-quality moving images cannot be displayed.

  The object of the present invention is to detect a face part that is highly likely to be viewed by the viewer even when the entire screen is a moving picture or when the moving picture exists in a plurality of non-continuous blocks. It is an object of the present invention to provide a liquid crystal display device that prevents a situation where the lighting control that should be performed originally is not performed and the quality of moving image display is not improved by improving the moving image quality, and expands the effect of improving motion blur.

  The liquid crystal display device of the present invention has face detection means for detecting a person's face from a video signal, and passes when the luminance level of the video signal is a first value and is a second value smaller than the first value. Is compared with the output of the previous frame by comparing the output of the edge detection circuit with the brightness determination means for blocking, the edge detection means for extracting and outputting the contour of the video signal by high-pass filtering the output of the brightness determination means. A motion amount detection unit that detects a motion amount for each line, a moving image line determination unit that determines whether each line is a moving image line based on a detection result of the motion amount detection unit, and a face detection unit that Of the lines where the face is detected, the video block identifying means for identifying the video lines continuous before and after the fastest video line as the fastest video block, and writing the fastest video block part on the liquid crystal panel In accordance with the in which the timing, in which and a PWM pulse generating means for outputting a PWM pulse which turns off the backlight.

In the liquid crystal display device according to the present invention, the period of data writing is not displayed by turning off the backlight for a certain period from the start point of the panel scanning the area corresponding to the vertical position where the detected moving image exists, Improving the quality of the video quality by bringing the display closer to the impulse type, even if the entire screen is a video or even if the video is in multiple non-consecutive blocks,
Extract video contours and human face information, detect the amount of motion for each video line, select a portion that is a moving image and where motion blur is conspicuous, that is, a portion that has a high improvement effect on motion blur, and a backlight control signal By adjusting the waveform and phase, it is possible to prevent the situation where the lighting control that should be performed originally is not performed and the moving image display quality is not improved, and the effect of improving the motion blur of moving image display can be expanded.

  According to the liquid crystal display device of the present invention, it is possible to realize a liquid crystal display device that expands the display moving image response improvement effect.

  Hereinafter, an embodiment of a liquid crystal display device according to the present invention will be described with reference to the drawings. Note that the liquid crystal display device to which the present invention is applied is not particularly limited to this example, and can be easily applied to liquid crystal display devices other than those described in the examples without departing from the spirit of the invention. Needless to say.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a liquid crystal display device according to an embodiment of the present invention. 2 and 3 are conceptual diagrams of basic operations. FIG. 4 is an operation explanatory diagram when the entire screen is a moving image or when the moving image exists in a plurality of non-continuous blocks.

  The liquid crystal display device shown in FIG. 1 includes a liquid crystal panel 10 that displays an input video signal, a backlight 11 that visualizes the video displayed on the liquid crystal panel 10, and a face detection unit that detects a human face from the video signal. 12, a luminance determination unit 13 for selecting a video signal having a luminance level equal to or higher than a certain value, an edge detection unit 14 for extracting a contour based on the luminance level of the video signal, and a motion amount of the video based on the extracted contour information. Motion amount detection means 15 to detect, video line determination means 16 for determining a video line based on the motion amount of video, and video block specification for specifying a continuous video line as a video block according to the output of the video line determination means 16 PWM pulse generating means for generating a control signal for controlling blinking of the backlight 11 according to the output of the means 17 and the moving picture block specifying means 17 Consisting of 8.

  The face detection means 12 extracts a face portion such as the eyes, nose and mouth from the video signal based on the brightness difference, and detects the face of the person.

  The luminance determination means 13 is intended to extract a character signal with noticeable motion blur and a signal with high luminance. The predetermined luminance level is set as a threshold value, and when the luminance level of the input video signal is a certain value or more, the video signal is passed. When the luminance level of the input video signal is less than a certain value, the video signal is blocked and a black signal is output. Here, the black signal is a signal indicating that the luminance level of the video signal input to the luminance determining means 13 is less than a certain value, and is equivalent to a video signal having a luminance level of zero.

  The edge detection unit 14 performs high-pass filter processing on the output of the luminance determination unit 13 and extracts the contour of the video. The edge detection means 14 outputs the absolute value of the output of the high pass filter.

  The motion detector 15 receives the output of the edge detector 14 as an input. The input signal of the current frame and the input signal of the previous frame are compared in units of pixels, and a value obtained by accumulating the absolute value of the difference for one horizontal scanning period is output. When the motion is detected with respect to a signal obtained by extracting a bright outline in which motion blur is conspicuous, the output of the motion detection means 15 becomes a larger value as the motion increases.

  The moving image line determination means 16 determines whether or not the scanning line is a moving image line based on whether or not the output of the motion detection means 15 exceeds a set threshold value. If it exceeds the set threshold, it is determined as a video line and an H level signal is output. If it does not exceed the set threshold, it is determined as a static line and an L level signal is output.

  The moving image block specifying means 17 selects the line that is the maximum value in one vertical period of the output value of the motion detecting means 15 from the video lines determined to be the moving image line by the moving image line determining means 16, so that one vertical period is reached. Identify the fastest moving line. A moving image line continuous before and after the identified fastest moving line is set as the fastest moving image block, and it is determined whether or not a face image is included in the fastest moving image block. When face video is not included in the fastest video block, the second fastest moving video line is identified, and the video line continuous before and after the identified line is newly set as the fastest video block, and the face video is included in the fastest video block. Determine whether it is included. If face video is not included in the fastest video block, the next fastest moving video line is identified, the video line continuous before and after the identified line is newly set as the fastest video block, and the fastest video block contains face video To determine whether or not The above operation is sequentially repeated, and among the moving image blocks including the face image, the moving image block including the moving image line with the fastest motion is set as the fastest moving image block.

  The PWM pulse generation means 18 generates a drive voltage waveform (PWM pulse) so that the backlight 11 is turned off in accordance with the timing at which the moving image block portion specified by the moving image block specifying means 17 is written in the liquid crystal panel 10. To do.

  The basic operation will be described with reference to FIGS. The basic backlight extinguishing period when supporting a moving image is set in advance from the reference screen brightness. As an example, assume that 70% of one vertical synchronization period is turned on and 30% is turned off.

  FIG. 2 is a diagram illustrating the on-off timing of an image displayed on the liquid crystal panel 10 and the PWM pulse. The liquid crystal display device according to the present embodiment scans an area corresponding to the vertical position where the moving image specified by the moving image block specifying unit 17 exists based on the signal determined by the moving image line determining unit 16 for each scanning line. When doing so, the PWM pulse is controlled so that the backlight 11 is turned off. That is, the backlight turn-off timing and the signal writing timing to the moving image existence scanning line are made to coincide with each other for each frame of the video. By doing so, the change video during the data rewriting period of the moving image on the liquid crystal panel 10 is not displayed, and the image before rewriting and the video after rewriting are displayed. Further, during this period, the black display effect by turning off the backlight brings the hold type display closer to the impulse type, and the moving image quality can be improved by suppressing the moving image blur.

  A specific description will be given with reference to FIG. FIG. 3 is a diagram showing the relationship between video writing timing, backlight lighting time, and visually recognized video. When the data enable is at the H level, it is an image writing period. The data writing image indicates an image of a video displayed on the liquid crystal panel 10. The backlight lighting period indicates the on / off timing of the backlight. The visual image indicates an image visually recognized by the viewer.

  As shown in FIG. 3, since the backlight is turned off during the moving image writing period, the moving image blur can be suppressed and the moving image quality can be improved.

  The operation when there are a plurality of non-consecutive moving image blocks in FIG. 4 or when there is a moving image block having a size exceeding the extinguishing period will be described.

  In I of FIG. 4, there are a plurality of moving image blocks A, B, and C that are not continuous. Here, it is assumed that the moving image blocks A, B, and C do not include face images. In this case, the extinction phase of the PWM pulse is controlled in accordance with the start phase of the moving image block including the fastest moving line. In the case of I in FIG. 4, since the fastest line is included in the moving image block A, the phase of the PWM pulse is controlled so that the backlight is turned off in accordance with the start phase of the moving image block A.

  In II of FIG. 4, there are a plurality of moving image blocks D and E that are not continuous. Here, it is assumed that the moving image blocks D and E do not include a face image, and the moving image block D is a moving image block having a size exceeding the extinguishing period. Also in this case, the extinction phase of the PWM pulse is controlled in accordance with the start phase of the moving image block including the fastest moving line. In the case of II in FIG. 4, since the fastest moving line is included in the moving image block D, the phase of the PWM pulse is controlled so that the backlight is turned off in accordance with the start phase of the moving image block D.

  In III of FIG. 4, there are a plurality of moving image blocks F and G that are not continuous. Here, the moving image block F does not include a face image, and the moving image block G includes a face image. In this case, the block including the face image is selected as the fastest moving image block in preference to the moving image block including the fastest moving line. In the case of III in FIG. 4, since there is a moving image block F including a face image, the PWM pulse is turned off so that the backlight is turned off in accordance with the start phase of the moving image block F, not the moving image block G including the fastest moving line. Control the phase of.

  As described above, when there are a plurality of video blocks that are not continuous in the past or there are video blocks with a size longer than the extinguishing period, the false contour is considered to be improper in the timing of the flashing of the backlight and the liquid crystal response. In the past, since the quality of the moving image is not improved because of the occurrence of the image, the image that can obtain the effect is limited to a specific pattern, and most of the moving image is not applicable. In this case, even if there are multiple non-consecutive video blocks or there are video blocks with a size longer than the turn-off period, the motion blur in the video is conspicuous and the improvement effect is high The video quality is improved by inserting black with the aim of. Therefore, the pseudo contour generated in the portion where the timing of the blinking of the backlight and the liquid crystal response is not appropriate is generated in the portion that is not visually conspicuous.

  The relationship between the moving image speed and the motion blur is not visible when the speed is slow and close to a still image, but the motion blur gradually becomes more noticeable as the speed increases. However, if the speed exceeds a certain speed, the presence / absence of motion blur itself cannot be identified. Therefore, if the motion is slow and the motion blur is not visually recognized, or the motion is too fast to identify the motion blur, it is better to remove the motion blur to improve the motion blur. It is possible to improve the video quality by selecting a portion with high effect.

  In order to realize the above, for example, an upper limit value and a lower limit value obtained by accumulating the absolute value of the difference between the input signal of the frame and the input signal of the previous frame detected by the motion detection unit 15c for one horizontal scanning period. Can be dealt with by not detecting it as a motion in the motion detection circuit 15 if, for example, the speed x of the moving image is other than the lower limit value ≦ x ≦ the upper limit value.

In the embodiment of the present invention, the control is performed so that the start phase of the PWM pulse matches the start phase of the video block including the fastest moving video line, but the center phase of the selected video block, The center phase of the PWM pulse extinguishing period may be matched.
Alternatively, the extinction start phase of the PWM pulse may be matched with the fastest moving video line.

  In this way, for example, the video block including the fastest moving video line is larger than the turn-off period, and the phase difference between the moving block start phase and the fastest moving video line exceeds the turn-off period. Even in the case of the size, since the extinction phase of the PWM pulse overlaps in the writing period of the fastest moving video line, the occurrence of pseudo contours around the fastest moving video line that is visually blurred is prevented, It becomes possible to suppress blurring of the video.

  Further, in the embodiment of the present invention, when there are a plurality of non-consecutive moving image blocks or when there is a moving image block whose size is longer than the turn-off period, the lighting phase control is performed by paying attention to the moving image line with the fastest movement. However, the start line of the largest video block may be used as a reference.

  By doing this, the PWM pulse extinguishing period that can achieve the motion blur improvement effect can be overlapped with the motion block writing period as much as possible, and the motion blur improvement effect can be obtained over a wide motion region. It becomes.

  In addition, if the entire screen is a moving image, but the movement is uniform, and a specific line is not selected as the fastest moving line, the moving image quality at the center of the screen where humans tend to focus on the image is high. The backlight may be turned off at the center of the screen to improve the situation.

  By doing this, the fastest moving line is not identified, and the extinction phase of the PWM pulse fluctuates, so that the area that improves motion blur and the area where the pseudo contour is generated are prevented from fluctuating and It is possible to suppress motion blur by fixing the extinction phase of the PWM pulse at the center of the screen where people tend to focus on it.

  As described above, in the first embodiment, the data writing period is not displayed by turning off the backlight for a certain period from the start point at which the panel scans the detected moving image, and the display is made closer to the impulse type to display the moving image. In addition to improving the quality of the quality, even if the entire screen is a video or even if the video is present in multiple blocks that are not continuous, the contours of the video and face information of the person are extracted, and the fastest moving part is extracted. By selecting and adjusting the control signal waveform and phase of the backlight, a portion that is a moving image and where motion blur is conspicuous, that is, a portion that has a high improvement effect on motion blur is selected, and the control signal waveform and phase of the backlight are selected. By adjusting the, it is possible to prevent the situation where the lighting control that should be performed originally is not performed and the video display quality is not improved, and to improve the display video response improvement effect. That.

  The liquid crystal display device according to the present invention hides the data writing period by turning off the backlight for a certain period from the starting point at which the panel scans the detected moving image, and makes the display close to the impulse type to improve the moving image quality. In addition to improving the quality, even if the entire screen is a moving image or when the moving image exists in a plurality of non-continuous blocks, the contour of the image and the face information of the person are extracted, and the most moving in one vertical period By selecting the fast part and adjusting the control signal waveform and phase of the backlight, the moving picture and the part where the motion blur is conspicuous, that is, the part that has a high improvement effect on the motion blur is selected to improve the video display quality. Therefore, it is possible to realize a liquid crystal display device that prevents the situation where the lighting control that should be performed originally is not performed and the moving image display quality is not improved, and that the display moving image response improving effect is expanded. A shall, useful as a liquid crystal display device such as a projector having a liquid crystal television or a backlight having a backlight.

1 is a block diagram showing a configuration of a liquid crystal display device described in Embodiment 1 of the present invention. Diagram showing on-off timing of video and PWM pulse displayed on liquid crystal panel The figure which shows the relationship between the timing of video writing, the lighting time of the backlight, and the visual image FIG. 5 shows an operation of the liquid crystal display device described in Embodiment 1 of the present invention. Block diagram showing the configuration of a conventional liquid crystal display device

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal panel 11 Backlight 12 Face detection means 13 Luminance determination means 14 Edge detection means 15 Motion amount detection means 16 Movie line determination means 17 Movie block identification means 18 PWM pulse generation means

Claims (5)

Face detection means for detecting a human face from a video signal;
A luminance determining means for allowing the luminance level of the video signal to pass when it is a first value and blocking when the luminance level is a second value smaller than the first value;
Edge detection means for performing high-pass filter processing on the output of the luminance determination means and extracting and outputting the contour of the video signal;
Compared with the output of the previous frame for the output of the edge detection circuit, a motion amount detection means for detecting the motion amount for each line;
Based on the detection result of the motion amount detection means, a video line determination means for determining whether each line is a video line,
Among the lines in which the face detection means detects a person's face, a video block specifying means for specifying a video line continuous before and after the fastest video line as the fastest video block;
A liquid crystal display device comprising: a PWM pulse generating means for outputting a PWM pulse for turning off the backlight in accordance with the timing at which the fastest moving image block portion is written in the liquid crystal panel. If the face detection means does not detect a person's face,
2. The liquid crystal display device according to claim 1, wherein the moving image block specifying unit specifies moving image lines continuous before and after the fastest moving image line as the fastest moving image block. 3. The liquid crystal display device according to claim 1, wherein the backlight is switched off at a timing when a video signal is written to a start line of the fastest moving image block in the liquid crystal panel. The moving image block specifying means includes:
4. The liquid crystal display device according to claim 1, wherein the fastest moving image line is identified from moving image lines having a motion amount of each line equal to or less than a predetermined value. 5. The moving image block specifying means includes:
5. The liquid crystal display device according to claim 1, wherein when there are a plurality of the fastest moving image lines, the central portion of the liquid crystal panel is specified preferentially.

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