JP4605654B2 - Video signal processing device and display device equipped with the same - Google Patents

Description

  The present invention relates to a technique for processing a video signal.

  In a device (for example, a television receiver) that processes a video signal, for example, the maximum level, minimum level, and average luminance level values of the luminance signal of the input video are detected, and the contrast is adjusted based on these values. The thing is known (for example, patent document 1).

Japanese Patent No. 3215400 (FIGS. 1 and 36)

  In the prior art disclosed in Patent Document 1, the characteristics of the input video signal are detected, and the gain (also referred to as “gain”) is adjusted to increase the contrast in accordance with the dynamic range of the display device. Usually, increasing the contrast increases the gain. However, as the gain increases, the amplitude of the video increases, and in conjunction therewith, noise included in the video (for example, white noise, mosquito noise, etc., hereinafter referred to as a noise component) is also amplified. For this reason, the video signal at the time of output may be more disturbed than the video signal at the time of input.

  As described above, the conventional technique does not consider the problem of emphasizing noise components in contrast adjustment (particularly, adjustment for increasing gain).

  Accordingly, an object of the present invention is to provide a technique for improving the image quality of an image whose gain (in particular, gain related to contrast adjustment) is adjusted.

  A video signal processing device according to one aspect of the present invention includes a noise reduction unit that reduces a noise component of an input video signal based on a noise suppression amount, and a video adjustment unit that adjusts the input video signal according to a gain. Prepare. This video signal processing device increases the amount of noise suppression for a video signal that is adjusted so as to increase the gain as compared with the amount of noise suppression for other video signals. This process may be performed by at least one of the noise reduction unit and the video adjustment unit, or may be performed by a control unit that controls the noise reduction unit and the video adjustment unit. In addition, the video adjusting unit can perform the above adjustment on the video signal that has been processed by the noise reducing unit.

  In one embodiment, the video signal processing apparatus may further include a detection unit that detects a gradation value distribution representing the number of pixels for each gradation value from a video signal for one screen including a plurality of pixels. In this case, the video signal processing apparatus can adjust the gain based on the detected gradation value distribution. In addition, the video signal processing device identifies a special gradation value range having a number of pixels equal to or greater than a certain threshold from the gradation value distribution, and for a video signal of pixels belonging to the specified special gradation value range. Adjustments that increase the gain can be made. Further, the video signal processing apparatus performs an adjustment for increasing the gain only for the video signal of the pixel belonging to one range with the reference grayscale value as a boundary in the special gradation value range, and the video of the pixel belonging to the other range The signal may not be adjusted to increase the gain. Alternatively or in addition, the video signal processing apparatus performs an adjustment to increase the gain only for the video signal of the pixel belonging to the low gradation value side in the special gradation value range, and the pixel of the pixel belonging to the high gradation value side is adjusted. It is also possible not to perform adjustment for increasing the gain of the video signal.

  In one embodiment, the video signal processing apparatus may further include contour correction means for performing contour correction on the input video signal based on a contour correction amount. In this case, the video signal processing apparatus can adjust the contour correction amount together with the adjustment of the gain and the noise suppression amount. Specifically, for example, the video signal processing device may reduce a contour correction amount for a video signal that is adjusted to increase the gain to be smaller than a contour correction amount for other video signals. it can.

  In one embodiment, the image adjusting means can adjust the contrast of the input image signal according to the adjusted gain. In this case, for example, the video signal processing apparatus can further include a detection unit that detects a luminance distribution representing the number of pixels for each luminance from a video signal for one screen including a plurality of pixels. The video signal processing device identifies a special luminance range having a number of pixels equal to or greater than a certain threshold from the luminance distribution, and performs adjustment to increase gain for the video signal of pixels belonging to the specified special luminance range. Can do.

  A display device according to another aspect of the present invention includes a video signal processing device that processes and outputs an input video signal, and a display unit that displays a video represented by the video signal output from the video signal processing device. . The video signal processing apparatus includes a noise reduction unit that reduces a noise component of an input video signal based on a noise suppression amount, and a video adjustment unit that adjusts the input video signal according to a gain. The video signal processing device increases the noise suppression amount for the video signal that is adjusted so as to increase the gain more than the noise suppression amount for the other video signals.

  In one embodiment, the display device can adjust the brightness of an image displayed by the display unit in accordance with the adjustment of the gain and the noise suppression amount. Specifically, for example, the display unit may be a projection type display unit including a light source for displaying an image and a screen for projecting the image with light from the light source. The display device may further include detection means for detecting a luminance distribution representing the number of pixels for each luminance from a video signal for one screen composed of a plurality of pixels. The display device determines from the luminance distribution whether or not the video signal for one screen is dark. If it is determined to be dark, the display device reduces the illuminance of the light source, and determines the luminance distribution from a low luminance region. Adjustments that increase the gain can be made for locations determined to be present.

  According to the present invention, it is possible to suppress a noise component that is amplified by increasing a gain (particularly, gain related to contrast adjustment), and thus it is possible to improve the image quality of an image whose gain is adjusted.

  A video signal processing apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is a functional block diagram of a video signal processing apparatus according to the first embodiment of the present invention.

  The video signal processing apparatus described above has a video input terminal 1 for inputting a digital video signal (hereinafter referred to as “video signal”), and characteristics of the input video signal (for example, one screen of the video signal). And a noise reduction circuit 5 for reducing noise components of the input video signal. The video signal processing apparatus includes a contrast correction circuit 6 for correcting the contrast of the input video signal, a control circuit 4 for controlling the noise reduction circuit 5 and the contrast correction circuit 6, and a contrast correction circuit 6. A video output terminal 2 that outputs the output video signal (for example, outputs to a display unit such as a transmissive display device or a liquid crystal panel) is provided.

  Next, the flow of processing performed from when a video signal is input to the video input terminal 1 to when the video signal is output from the video output terminal 2 will be described with reference to FIG.

  First, the video signal input to the video input terminal 1 is output to the feature detection circuit 3 and the noise reduction circuit 5.

  The feature detection circuit 3 detects a feature of the input video signal, for example, a gradation value distribution (for example, luminance distribution) representing the number of pixels for each gradation value from a video signal for one screen composed of a plurality of pixels. The detection result is output to the control circuit 4.

  The control circuit 4 creates a control signal for noise reduction and contrast correction based on the detection result, and outputs the created control signal to the noise reduction circuit 5 and the contrast correction circuit 6. Specifically, for example, the control circuit 4 calculates a contrast correction amount and a noise suppression amount based on the contrast correction amount based on the detection result. The control circuit 4 controls the contrast correction circuit 6 to perform contrast correction based on the calculated contrast correction amount, and controls the noise reduction circuit 5 to perform noise reduction processing with the calculated noise suppression amount. To do.

  The noise reduction circuit 5 performs noise reduction processing based on the noise suppression amount according to the input control signal. Specifically, for example, the noise reduction circuit 5 performs a noise reduction process using the fact that there is no correlation between the noise components in the video by inter-frame calculation. Since this noise reduction processing method has various methods and is publicly known, detailed description thereof is omitted. Note that the noise reduction processing method does not have to be based on the inter-frame calculation, but may be an intra-field calculation or a horizontal low-pass filter.

  The video signal subjected to the noise reduction process is output from the noise reduction circuit 5 and input to the contrast correction circuit 6. Then, the contrast correction circuit 6 performs contrast correction on the input video signal based on the contrast correction amount determined by the control signal from the control circuit 4. The video signal subjected to the noise reduction processing and the contrast correction is output from the contrast correction circuit 6 and supplied to a display unit such as a transmissive display device or a liquid crystal panel via the video output terminal 2.

  FIG. 2 is a diagram illustrating characteristics of contrast correction.

  As shown in FIG. 2, the contrast correction is performed by changing the slope of the input / output characteristic graph of the video signal level, in other words, the contrast gain (hereinafter referred to as contrast gain). For example, if the slope of the graph (contrast gain) is 1, there is no change in contrast between the input and output, and if the slope of the graph is smaller than 1 (contrast gain <1), the contrast becomes smaller and the slope is smaller than 1. If it is increased (contrast gain> 1), the contrast is increased.

  FIG. 3 shows the relationship between the contrast gain and the noise suppression amount in this embodiment.

  In the present embodiment, when the correction for increasing the contrast is not performed (the contrast gain is 1 or less), the control circuit 4 sets the noise suppression amount to a normal amount (for example, a predetermined amount) and performs the correction for increasing the contrast. In the case (when the contrast gain exceeds 1), the noise suppression amount is set to be larger than the normal amount. By this processing, it is possible to suppress in advance the noise component that is amplified in conjunction with the correction for increasing the contrast.

  Next, calculation of the contrast correction amount and the noise suppression amount according to the embodiment will be described with reference to FIG.

  FIG. 4A shows an example of the luminance distribution detected by the feature detection circuit 3.

  Based on the detection result, the feature detection circuit 3 determines which gradation (for example, luminance level) has a high distribution, in other words, which luminance has a large number of pixels. Specifically, for example, a predetermined threshold “h1” is used for this determination process as shown in FIG. That is, the feature detection circuit 3 compares the number of pixels of each luminance with the threshold “h1”, and specifies a luminance range (hereinafter referred to as a special luminance range) having a number of pixels larger than the threshold “h1”. Here, as a luminance range having a distribution frequency higher than the threshold “h1” (that is, having a larger number of pixels than the threshold “h1”), a range of luminance LV1 to LV2 is determined as the special luminance range. The feature detection circuit 3 inputs the determined special luminance range to the control circuit 4.

  The control circuit 4 is based on the input special luminance range, the first control signal representing the special luminance range (LV1 to LV2), and the second for making the noise suppression amount larger than that outside the special luminance range. A control signal and a third control signal for making the contrast higher in the special luminance range than in other luminance ranges are generated and output. The second control signal includes, for example, a noise suppression amount for each luminance level in the special luminance range (for example, the noise suppression amount illustrated in FIG. 4C). The third control signal includes, for example, a contrast correction amount (for example, the contrast correction amount illustrated in FIG. 4B).

  FIG. 4B shows an example of the contrast correction amount based on the luminance distribution of FIG.

  In the figure, the horizontal axis represents the luminance of the input video signal (hereinafter referred to as input luminance), and the vertical axis represents the luminance of the output video signal (hereinafter referred to as output luminance). In normal operation (in the state where no control signal is input from the control circuit 4), the input / output characteristics are assumed to be linear as indicated by the alternate long and short dash line.

  The contrast correction amount can be represented by, for example, a contrast gain and coordinates at which it is changed, as shown in FIG. 4B. The contrast correction amount shown in FIG. 4B includes, for example, a contrast gain from the input luminance 0, a contrast gain from the input luminance LV1, and a contrast gain from the first input luminance on the LV1 side in the special luminance range. It can be expressed by the contrast gain from the second input luminance on the LV2 side in the special luminance range and the contrast gain from the input luminance LV2.

  The contrast correction circuit 6 performs contrast correction according to the contrast correction amount included in the third control signal from the control circuit 4. That is, the contrast correction circuit 6 makes the slope of the input / output characteristic (that is, contrast gain) steep in the special luminance range (LV1 to LV2 range) indicated by the first control signal output from the control circuit 4, and the luminance distribution In other small luminance regions (luminance region lower than LV1 and luminance region higher than LV2), control is performed so that the slope is more gentle than that. In this embodiment, by controlling in this way, it is possible to improve the contrast of luminance with a large distribution in one image.

  In this embodiment, in the special luminance range, the contrast gain is larger in the vicinity of the boundary with the other luminance ranges than in the other luminance ranges, but is smaller than the contrast gain in the central range of the special luminance range. Is done. As a result, it is possible to output a video having a good image quality with a difference in contrast strength suppressed.

  FIG. 4C shows an example of a noise suppression amount based on the contrast correction amount of FIG.

  The noise reduction circuit 5 also receives the first control signal and the second control signal from the control circuit 4. Then, the noise reduction circuit 5 determines the noise suppression amount in the special luminance range (LV1 to LV2 range) indicated by the first control signal as shown in FIG. (Luminance region over LV2) is controlled to be larger than the amount of noise suppression.

  By controlling in this way, when the correction for increasing the contrast is performed, the amount of noise suppression is increased. Therefore, the noise component to be amplified can be reduced by increasing the contrast, and thus a high-quality image is obtained. be able to.

  As described above, according to the first embodiment, the noise suppression amount is increased from the normal amount in conjunction with increasing the contrast (for example, increasing the contrast gain higher than 1). As a result, it is possible to reduce noise components that are amplified as the contrast is increased.

  Further, according to the first embodiment, the luminance distribution for one screen of the video is detected, and in the special luminance range that is a luminance range having a large luminance distribution, the correction for increasing the contrast and the amount of noise suppression are increased. Is called. Thereby, a noise component can be suppressed and contrast can be raised.

  Next, another embodiment of the present invention will be described. In the following, differences from the first embodiment will be mainly described, and description of common points with the first embodiment will be omitted or simplified.

  FIG. 5 is a functional block diagram of the video signal processing apparatus according to the second embodiment of the present invention. In addition, the thing of the same code | symbol as FIG. 1 shall have the same function.

  Suppressed luminance is input to the control circuit 4 from the suppressed luminance input terminal 7. Suppressed luminance is luminance that serves as a reference in which range in the special luminance range to increase the amount of noise suppression.

  The control circuit 4 performs control so that the amount of noise suppression in the noise reduction circuit 5 is increased at a luminance lower than that based on the suppression luminance set by the suppression luminance input terminal 7. An example of the operation is shown in FIG.

  FIG. 6A shows an example of the luminance distribution detected by the feature detection circuit 3 in the second embodiment. FIG. 6B shows an example of the contrast correction amount based on the luminance distribution of FIG. FIG. 6C illustrates an example of a noise suppression amount based on the contrast correction amount illustrated in FIG. 6B and the input suppression luminance.

  A luminance range having a number of pixels larger than a predetermined threshold value “h2” is input from the feature detection circuit 3 to the control circuit 4 as a special luminance range. Further, the suppressed luminance is input to the control circuit 4 via the terminal 7.

  As in the first embodiment, the control circuit 4 controls the contrast correction circuit 6 so that the slope of the input / output characteristics (contrast gain) is steep in the special luminance range, as shown in FIG. 6B. To do. However, as shown in FIG. 6C, the control circuit 4 increases the noise suppression amount only in the range below the suppression luminance, as shown in FIG. Then, the noise reduction circuit 5 is controlled so that the amount of noise suppression is smaller than that.

  As described above, according to the second embodiment, the noise suppression amount is increased in the low luminance range where noise is relatively conspicuous, and the noise suppression amount is decreased in the high luminance range where noise is relatively inconspicuous. For this reason, it is advantageous when the luminance range in which noise is conspicuous is known in advance, and the adverse effect on the original video due to the noise reduction processing in the high luminance range can be reduced.

  In the second embodiment, for example, the suppression luminance input to the control circuit 4 may be a predetermined fixed value, may be a value selected by the user, or may be input. It may be a value selected by the control circuit 4 from a plurality of suppressed luminances based on the characteristics of the video signal.

  FIG. 7 is a functional block diagram of a video signal processing apparatus according to the third embodiment of the present invention.

  In the third embodiment, a contour correction circuit 8 is provided between the contrast correction circuit 6 and the output terminal 2. The image on which the contrast correction has been performed is input to the contour correction circuit 8, the contour correction is performed in the circuit 8, and then output via the output terminal 2. The contour correction circuit 8 operates under the control of the control circuit 4. Specifically, for example, when the contrast gain is increased from 1 and the noise suppression amount is increased for a pixel having a certain luminance, the contour correction circuit 8 sets the contour correction amount for at least that pixel to the other pixel. Less than that.

  According to the third embodiment, when the contrast is increased, the noise component can be reduced and the enhancement of the remaining noise component can be prevented by reducing the contour correction amount. Obtainable.

  FIG. 8 is a block diagram of a television receiver according to the fourth embodiment of the present invention.

  The television receiver includes, for example, a video signal processing device according to the first embodiment and a projection display device 20. The projection display device 20 includes, for example, a light source 21, a transmissive display element 22, and a screen 23. The video signal output from the contrast correction circuit 6 is input to the transmissive element 22, and an image represented by the video signal input to the transmissive element 22 is projected onto the screen 23 by irradiation from the light source 21.

  The control circuit 4 controls the light source 21 of the projection display device 20 in addition to the noise reduction circuit 5 and the contrast correction circuit 6.

  For example, the control circuit 4 can determine whether or not the video is entirely dark from the detected luminance distribution. When it is determined that a video image that is entirely dark is input, the control circuit 4 performs control so as to reduce the illuminance of the light source 21 so that the entire video image does not become whitish. Further, when it is determined that a dark video is input as a whole, the luminance distribution detected by the feature detection circuit 3 shows a high distribution in a low luminance region, so that the control circuit 4 increases the contrast in the low luminance region. Thus, the contrast correction circuit 6 is controlled.

  That is, in this embodiment, when a dark image is input as a whole, the illumination of the light source 21 is reduced and the contrast correction circuit 6 corrects the contrast (correction according to a contrast gain greater than 1). By controlling in this way, the contrast of dark images can be increased. In the low luminance region, control is performed by the control circuit 4 so that the amount of noise suppression increases.

  In this embodiment, for example, instead of or in addition to controlling the illuminance of the light source 21, the transmittance of the transmissive element 22 that transmits light emitted from the light source 21 may be controlled. Specifically, for example, the transmissive element 22 receives the contrast correction amount from the contrast correction circuit 6 together with the video signal subjected to the contrast correction, and is based on the contrast correction amount (particularly, the contrast gain in the special luminance range). Thus, the transmittance may be controlled.

  As mentioned above, although several Example of this invention was described, these Examples are only the illustration for description of this invention, and is not the meaning which limits the scope of the present invention only to these Examples. The present invention can be implemented in various other modes without departing from the gist thereof.

  For example, the video signal processing device according to the present invention is used in a display device such as a television receiver, but is a digital device that receives a digital television broadcast signal called a VTR, a DVD device, or a set top box (STB). It can be similarly used for a device such as a tuner that does not have a display portion.

  Further, for example, in each of the above-described embodiments, the contrast correction is performed after the noise reduction process is performed (that is, after the noise component is suppressed in advance), but conversely, after the contrast correction is performed, Noise reduction processing may be performed.

  Further, for example, the histogram detected by the feature detection circuit 3 is not limited to luminance, and may be a histogram based on other types of gradation values. Further, the gradation values such as luminance are not limited to 256 gradations, and may be more or less than that.

1 is a functional block diagram of a video signal processing apparatus according to a first embodiment of the present invention. It is a figure which shows the characteristic of contrast correction. The relationship between the contrast gain and the noise suppression amount in the present embodiment is shown. FIG. 4A shows an example of the luminance distribution detected by the feature detection circuit 3. FIG. 4B shows an example of the contrast correction amount based on the luminance distribution of FIG. FIG. 4C shows an example of a noise suppression amount based on the contrast correction amount of FIG. The functional block diagram of the video signal processing apparatus which concerns on 2nd Example of this invention is shown. FIG. 6A shows an example of the luminance distribution detected by the feature detection circuit 3 in the second embodiment. FIG. 6B shows an example of the contrast correction amount based on the luminance distribution of FIG. FIG. 6C illustrates an example of a noise suppression amount based on the contrast correction amount illustrated in FIG. 6B and the input suppression luminance. The functional block diagram of the video signal processing apparatus which concerns on 3rd Example of this invention is shown. The block diagram of the television receiver which concerns on 4th Example of this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Video input terminal, 2 ... Video output terminal, 3 ... Feature detection circuit, 4 ... Control circuit, 5 ... Noise reduction circuit, 6 ... Contrast correction circuit, 7 ... Suppression luminance input terminal, 8 ... Contour correction circuit, 20 ... Projection type display device, 21 ... light source, 22 ... transmissive element, 23 ... screen

Claims (4)

A light source that emits light;
And noise reducing means for reducing based noise components of the input video signal to the noise reduction amount,
Video adjusting means for adjusting the video signal from the noise reducing means according to a gain determined by input / output characteristics;
A transmissive display element that forms an image using light emitted from the light source based on the image signal adjusted by the image adjusting means;
A gradation value distribution representing the number of pixels for each gradation value is detected from the input video signal for one screen composed of a plurality of pixels, and the number of pixels equal to or greater than a certain threshold is detected from the detected gradation value distribution. Detecting means for determining a special gradation value range having;
Control means for controlling the light source, the noise reduction means, and the image adjustment means based on the special gradation value range determined by the detection means;
The control means includes
The image adjusting means is controlled to make the slope of the input / output characteristic in the special gradation value range steeper than the input / output characteristic in another gradation value range, and the noise suppression in the special gradation value range Controlling the noise reduction means to make the amount larger than the noise suppression amount in the gradation value range other than the special gradation value range; and
When the low luminance area of the gradation value distribution is the special gradation value range, the input video signal is controlled to reduce the illuminance of the light source as a dark image.
A video display device characterized by that.   The video display device according to claim 1, wherein an image of the transmissive display element is projected on a screen.   2. The video display device according to claim 1, wherein the control unit controls the noise reduction unit so as to increase a noise suppression amount in the special gradation value range and not more than a predetermined suppression luminance range. A video display device characterized by that. 2. The video display device according to claim 1, further comprising contour correction means for performing contour correction of the input video signal, wherein the control means converts the contour correction amount in the special gradation value range to another gradation value range. a video display device comprising a to Turkey smaller than the contour correction amount in.

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