WO2011061888A1 - Video signal processing device and video display apparatus - Google Patents

Abstract

A video display apparatus (10) is provided with a contrast gain adjustment unit (3) which adjusts the contrast gain of a video signal, an error diffusion unit (11, 12, 13) which performs error diffusion on the video signal the contrast gain of which is adjusted by the contrast gain adjustment unit (3), and an error diffusion effect switching unit (4) which switches the error diffusion effect by changing the number of bits to be diffused as errors by the error diffusion unit (11, 12, 13) according to the contrast gain of the video signal.

Description

Video signal processing device and video display device

The present invention relates to a video signal processing apparatus that performs signal processing for improving image quality on a video signal, and a video display apparatus including the same.

In video display devices, various video signal processing is performed for the purpose of improving the quality of video. For example, Patent Document 1 discloses edge enhancement processing for emphasizing a contour portion of an image and displaying it as an image with a high apparent resolution, and dither processing for smoothing the gradation of the image as video signal processing. .

Also, in video equipment such as a television receiver, a feature amount (average brightness, maximum brightness, minimum brightness, etc.) is detected from a video signal to discriminate a video scene, and a contrast gain is adjusted according to the video scene. There is also a technology that realizes higher image quality.

In the contrast gain adjustment process as described above, a strong gain is applied to a specific gradation area (luminance area) of an image. For example, for a video signal having a dynamic range as shown in FIG. 2, a gain of ₂ is applied to the luminance i ₁ to i ₂ region of the input video signal as shown in FIG. As described above, it is assumed that the gradation correction for expanding the dynamic range of the video signal is performed. In this case, there is a problem that in the portion to which the gain is strongly applied (dotted line portion in FIG. 4), the gradation difference becomes larger than that in the other portions, and a pseudo contour is generated, which causes a reduction in video quality. Arise.

Also, even in the same gradation (that is, the number of bits of the video signal is the same), there is a color gamut in which pseudo contours are easily noticeable due to human visual characteristics. In this regard, in the conventional video signal processing technique, signal processing according to the color gamut of the video is not performed, and depending on the color gamut of the video, the pseudo contour is conspicuous and the video quality is deteriorated.

JP 2005-151305 A

The present invention has been made to solve the above problem, and an object thereof is to provide a video signal processing device and a video display device capable of improving video quality by suppressing the occurrence of pseudo contours. To do.

A video signal processing apparatus according to an aspect of the present invention includes a contrast gain adjusting unit that adjusts a contrast gain of a video signal, and error diffusion that performs error diffusion on the video signal whose contrast gain is adjusted by the contrast gain adjusting unit. And an error diffusion effect switching unit that switches the error diffusion effect by changing the number of bits that the error diffusion unit diffuses as an error according to the contrast gain of the video signal.

According to the above configuration, the contrast gain of the video signal is adjusted by the contrast gain adjustment unit. At this time, the larger the gain applied to the video signal, the larger the gradation difference and the more likely the pseudo contour is generated. Therefore, in the present invention, error diffusion processing is performed by the error diffusion unit on the video signal whose contrast gain has been adjusted. In this error diffusion process, the error diffusion effect switching unit switches the error diffusion effect by changing the number of bits for error diffusion according to the contrast gain of the video signal. As described above, the generation of the pseudo contour can be controlled by adaptively switching the error diffusion effect (changing the number of bits for error diffusion) according to the contrast gain. This is because as the error diffusion effect is increased (the number of bits for error diffusion is increased), the video is blurred and the pseudo contour is reduced. According to the configuration of the present invention, it is possible to enhance the error diffusion effect for a video signal having a large contrast gain. Therefore, it is possible to improve the video quality by suppressing the generation of pseudo contours.

A video signal processing apparatus according to another aspect of the present invention includes a color gamut detection unit that detects a color gamut of a video signal, an error diffusion unit that performs error diffusion on the video signal, and the color gamut detection unit detects And an error diffusion effect switching unit that switches the error diffusion effect by changing the number of bits that the error diffusion unit diffuses as an error according to the color gamut.

According to the above configuration, the error diffusion effect is adaptively switched according to the color gamut of the video signal (the number of bits for error diffusion is changed). Here, regarding the color gamut, even if the gradation is the same (that is, the number of bits of the video signal is the same), there are a color gamut in which false contours are conspicuous and a color gamut in which it is not so (for example, The blue color gamut is relatively more prominent in pseudo contour than the green color gamut). Further, as described above, as the error diffusion effect is increased (the number of bits for error diffusion is increased), the video is blurred and the pseudo contour can be reduced. Therefore, according to the configuration of the present invention, if the error diffusion effect is enhanced in a color gamut in which pseudo contour is more conspicuous, generation of pseudo contour can be suppressed and image quality can be improved.

A video display device according to still another aspect of the present invention includes the video signal processing device described above and a display unit that displays a video signal that has been subjected to signal processing by the video signal processing device.

With the above configuration, it is possible to realize a video display device capable of effectively suppressing the occurrence of pseudo contours and improving the video quality.

It is a schematic block diagram of the liquid crystal display device to which the video signal processing apparatus which concerns on this Embodiment is applied. It is explanatory drawing explaining the video signal before gradation correction. It is explanatory drawing which shows an example of the gamma curve for gradation correction. It is explanatory drawing explaining the video signal after gradation correction | amendment. It is a schematic block diagram of the other liquid crystal display device to which the video signal processing apparatus which concerns on this Embodiment is applied. It is a schematic block diagram of the liquid crystal display device which applied the alpha blend process to the video signal processing apparatus of FIG. 7 is a timing chart of various signals in the video signal processing apparatus of FIG. 6. It is a schematic block diagram of the further another liquid crystal display device to which the video signal processing apparatus which concerns on this Embodiment is applied. It is explanatory drawing for demonstrating the noise shaping effect. It is a schematic block diagram of the further another liquid crystal display device to which the video signal processing apparatus which concerns on this Embodiment is applied. It is a schematic block diagram of the further another liquid crystal display device to which the video signal processing apparatus which concerns on this Embodiment is applied.

Hereinafter, a video signal processing device and a video display device according to an embodiment of the present invention will be described with reference to the accompanying drawings. In addition, the following embodiment is an example which actualized this invention, Comprising: The thing of the character which limits the technical scope of this invention is not.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram of a liquid crystal display device 10 (video display device) to which the video signal processing device according to the present embodiment is applied. In FIG. 1, a liquid crystal display device 10 includes a feature amount detection unit 1, a contrast gain calculation unit 2 (error diffusion effect switching unit), a contrast gain adjustment unit 3, and a signal selection unit 4 (error diffusion effect) as a video signal processing device. A switching unit), a first noise shaping unit 11 (error diffusion unit), a second noise shaping unit 12 (error diffusion unit), a third noise shaping unit 13 (error diffusion unit), and bit number conversion units 14 to 16. Furthermore, the liquid crystal display device 10 includes a drive circuit 17 and a liquid crystal panel 18 (display unit).

In the present embodiment, the number of bits (number of gradations) of the video signal VS input to the liquid crystal display device 10 is described as 10 bits. However, the number of bits of the video signal VS is not limited to this. For example, it may be 8 bits, 12 bits, or other number of bits.

The feature amount detection unit 1 receives a video signal VS and a synchronization signal such as a vertical synchronization signal and a horizontal synchronization signal. The feature amount detection unit 1 detects the feature amount (average luminance (APL), maximum luminance, minimum luminance, luminance distribution, etc.) of the video signal VS for each frame (or for each field), and the detection result is obtained. Output to the contrast gain calculator 2. That is, the feature amount detection unit 1 calculates the video information of the entire screen at high speed, and detects the features of the video scene in real time for each frame. The feature amount detection unit 1 can detect the feature amount of the video signal VS for each frame of the progressive scanning video signal VS and for each field of the interlace video signal VS. In the following description, it is assumed that the feature quantity detection unit 1 detects a feature quantity for each frame.

The contrast gain calculation unit 2 calculates the contrast gain (gain of each gradation) of the video signal VS for each frame based on the feature amount of the video signal VS detected by the feature amount detection unit 1. That is, the contrast gain calculation unit 2 determines a gamma curve (gamma characteristic) suitable for the video scene based on the feature amount representing the feature of the video scene. The contrast gain calculation unit 2 then outputs the contrast gain calculation result to the contrast gain adjustment unit 3. Further, the contrast gain calculation unit 2 outputs a 2-bit selection control signal SC for selecting the output of the signal selection unit 4 to the signal selection unit 4. Details of the selection control signal SC will be described later.

The contrast gain adjusting unit 3 receives the video signal VS and the calculation result of the contrast gain. The contrast gain adjustment unit 3 includes a delay circuit (not shown) that delays the input video signal VS by one frame period during which the feature amount detection process is executed. Then, the contrast gain adjusting unit 3 adjusts the contrast gain of the video signal VS based on the calculation result of the contrast gain. In other words, the contrast gain adjustment unit 3 corrects the gamma curve in real time so as to realize the gradation appropriate for the detected feature of the video scene, and performs the gradation correction of the video signal VS.

The above-described feature amount detection unit 1, contrast gain calculation unit 2, and contrast gain adjustment unit 3 realize scene-adaptive contrast / gamma correction. For example, the contrast can be improved by applying a gain that expands the output signal level of the video signal VS to the maximum value based on the APL and maximum / minimum luminance of the video signal VS in one frame (one screen). . Also, based on the luminance distribution of the pixels in one frame (in one screen), gamma correction is performed so that more gradations are assigned to the luminance region with the largest video component, so that a contrast feeling in a dark scene, for example, can be obtained. Can be improved.

The contrast gain adjusting unit 3 adjusts the contrast gain of the video signal VS (10 bits) as described above, and then converts the video signal VS (10 bits) into the signal selection unit 4, the first noise shaping unit 11, and the second It outputs to the noise shaping part 12 and the 3rd noise shaping part 13, respectively.

The first noise shaping unit 11 performs error diffusion on the lower 2 bits of the input video signal VS composed of 10 bits by noise shaping (NS) processing, converts it into a video signal VS composed of 8 bits, and outputs it.

Also, the second noise shaping unit 12 performs error diffusion on the lower 4 bits of the input video signal VS composed of 10 bits by noise shaping processing, converts it into a video signal VS composed of 6 bits, and outputs it.

Also, the third noise shaping unit 13 performs error diffusion on the lower 6 bits of the input video signal VS composed of 10 bits by noise shaping processing, converts it into a video signal VS composed of 4 bits, and outputs it.

The first to third noise shaping units 11, 12, and 13 include, for example, an adder and a delay unit (not shown), and components of lower n bits (n is 2, 4, or 6) of the input video signal VS. It is also possible to adopt a configuration in which the lower n bits of information are diffused by the integration effect and pseudo gradation is reproduced by converting the signal into PWM (Pulse Width Modulation) and adding it to the upper bits.

In the first to third noise shaping units 11, 12, and 13, as the number of lower-order bits diffused by the noise shaping process increases, the image becomes blurred and contributes to the reduction of the occurrence of pseudo contours. It leads to improvement effect.

The 8-bit video signal VS output from the first noise shaping unit 11 is converted into a 10-bit video signal VS by adding “00” to the lower 2 bits in the bit number conversion unit 14, and then the signal selection unit 4 is input.

Similarly, the 6-bit video signal VS output from the second noise shaping unit 12 is converted into a 10-bit video signal VS by adding “0000” to the lower 4 bits in the bit number conversion unit 15, and then The signal is input to the signal selector 4. The 4-bit video signal VS output from the third noise shaping unit 13 is converted into a 10-bit video signal VS by adding “000000” to the lower 6 bits in the bit number conversion unit 16, and then the signal Input to the selector 4.

The signal selection unit 4 is a multiplexer that has four input streams and one output stream, and selects and outputs any one of the four input streams based on the 2-bit selection control signal SC. At each input terminal of the signal selection unit 4, the video signal VS output from the contrast gain adjustment unit 3 (not subjected to noise shaping processing), the video signal VS subjected to noise shaping processing by the first noise shaping unit 11, The video signal VS subjected to the noise shaping process by the second noise shaping unit 12 and the video signal VS subjected to the noise shaping process by the third noise shaping unit 13 are respectively input.

The signal selection unit 4 also receives a 2-bit selection control signal SC from the contrast gain calculation unit 2. The contrast gain calculation unit 2 sets the selection control signal SC so that a video signal VS having a larger noise shaping effect (that is, a larger number of lower bits diffused by the noise shaping) is selected in a luminance region having a higher contrast gain. Output to the signal selector 4.

In the present embodiment, as shown in FIG. 9, there is no noise shaping effect, noise shaping effect is small (10 → 8 bits), noise shaping effect is in effect (10 → 6 bits), and noise shaping effect is large (10 → 4 bits). ) Can be switched by selection in the signal selection unit 4. For example, if the contrast gain adjustment unit 3 can adjust the contrast gain from 1.00 times to 2.00 times, the gain range is set to the following four regions G ₀ , G ₁ , G ₂ , G _3. Can be divided equally.

1.00 ≦ G ₀ <1.25
1.25 ≦ G ₁ <1.50
1.50 ≦ G ₂ <1.75
1.75 ≦ G ₃ <2.00

For the video signal VS in the luminance region to which the gain G ₀ is applied in the contrast gain adjustment unit 3, the signal selection unit 4 selects that there is no noise shaping effect (the selection output from the contrast gain calculation unit 2 at this time). Control signal SC = "00"). Similarly, the video signal VS of the luminance regions where the gain _{G 1} is applied, the noise shaping effect small is selected (this time, SC = "01"). Further, the video signal VS of the luminance regions where the gain _{G 2} is applied during the noise shaping effect is selected (this time, SC = "10"). Further, the video signal VS of the luminance regions where the gain _{G 3} applied, the noise shaping effect size is selected (this time, SC = "11").

Of course, the contrast gain calculation unit 2 also receives a synchronization signal (vertical synchronization signal or horizontal synchronization signal) of the video signal VS. Therefore, the contrast gain calculation unit 2 switches the selection control signal SC according to the magnitude of the gain applied to the video signal VS in synchronization with the video signal VS.

In the above description, the possible gain range is 1.00 to 2.00 times, but the present invention is not limited to this. Further, the boundary (reference gains G ₀ to G ₃ ) for switching the degree of the noise shaping effect by equally dividing the possible gain range is set, but the present invention is not limited to this. That is, within the framework of increasing the noise shaping effect as the luminance region has a higher contrast gain, the gain range that can be taken is not divided equally but the reference gain can be arbitrarily set.

The drive circuit 17 drives the liquid crystal panel 18 using the video signal VS selected by the signal selection unit 4 as described above. Then, the liquid crystal panel 18 displays a video corresponding to the video signal VS.

The operation of the liquid crystal display device 10 having the above configuration will be described below.

The video signal VS input to the liquid crystal display device 10 is input to the feature amount detection unit 1 and the contrast gain adjustment unit 3. Then, the feature amount detection unit 1 detects the feature amount of the video signal VS for each frame, and outputs the detection result to the contrast gain calculation unit 2. The contrast gain calculation unit 2 calculates the contrast gain (gain of each gradation) of the video signal VS for each frame based on the detected feature amount of the video signal VS, and the calculation result is the contrast gain adjustment unit 3. Output to. The contrast gain adjustment unit 3 adjusts the contrast gain of the input video signal VS based on the calculation result of the contrast gain.

For example, let us consider a case where the contrast gain is adjusted with the gamma curve as shown in FIG. 3 for the input video signal VS having the dynamic range as shown in FIG. 2 by the above processing. That is, with respect to the input video signal VS, in the luminance region from 0 (black level) to the luminance i ₁ and from the luminance i ₂ to the luminance i ₃ (white level), the gain is 1 times, from the luminance i ₁ to the luminance i _2. It is assumed that a double gain is applied in the luminance region. As a result, the video signal VS output from the contrast gain adjusting unit 3 is subjected to gradation correction as shown in FIG. Note that the dotted line portion in FIG. 4 is a luminance region to which a double gain is applied.

At this time, the contrast gain calculation unit 2 sets the selection control signal SC to “11” during the period in which the video signal VS in the luminance region multiplied by the double gain is output from the contrast gain adjustment unit 3, The video signal VS subjected to the noise shaping process in the noise shaping unit 13 is selectively output from the signal selection unit 4. On the other hand, the contrast gain calculation unit 2 sets the selection control signal SC to “00” during the period when the video signal VS in the 1 × gain luminance region is output from the contrast gain adjustment unit 3, and the video signal VS without the noise shaping effect. Are selectively output from the signal selector 4.

Similarly, the contrast gain calculation unit 2 switches the selection control signal SC according to the magnitude of the contrast gain applied to the video signal VS, and the video signal VS without the noise shaping effect or the first to third noise shaping units 11, The video signal VS subjected to the noise shaping process in any one of 12 and 13 is selectively output from the signal selection unit 4.

As described above, the contrast gain calculation unit 2 switches the noise shaping effect in synchronization with the video signal VS according to the magnitude of the contrast gain applied to the video signal VS. As described above, a pseudo contour is more likely to occur in a luminance region having a larger contrast gain applied to the video signal VS. On the other hand, as the noise shaping effect is enhanced (the number of low-order bits diffused by noise shaping is increased), the image becomes blurred and contributes to the reduction of the occurrence of pseudo contour, leading to a substantial improvement in gradation. Therefore, the generation of pseudo contours can be effectively reduced by increasing the noise shaping effect in a luminance region having a larger contrast gain as in the present embodiment.

The video signal VS in which the generation of the pseudo contour is effectively reduced as described above is input to the drive circuit 17 that drives the liquid crystal panel 18, and a high-quality video corresponding to the video signal VS is displayed on the liquid crystal panel 18. The

The liquid crystal display device 10 has a configuration in which a plurality of noise shaping units (first to third noise shaping units 11, 12, 13) are connected in parallel. As shown in FIG. It can also be set as the structure connected in series.

The liquid crystal display device 20 shown in FIG. 5 includes first to third noise shaping units 21, 22, and 23 (error diffusion units) instead of the first to third noise shaping units 11, 12, and 13 of FIG. ing. Other basic configurations of the liquid crystal display device 20 are the same as those of the liquid crystal display device 10 of FIG.

In the liquid crystal display device 20, the video signal VS output from the contrast gain adjustment unit 3 is input to the first noise shaping unit 21 and the signal selection unit 4. The first noise shaping unit 21 performs error diffusion on the lower 2 bits of the 10-bit video signal VS input from the contrast gain adjustment unit 3 by noise shaping processing, converts the error signal into an 8-bit video signal, and outputs the video signal. To do. The video signal output from the first noise shaping unit 21 is input to the second noise shaping unit 22 and is converted into a 10-bit video signal by adding “00” to the lower 2 bits in the bit number conversion unit 14. Then, the signal is input to the signal selector 4.

Also, the second noise shaping unit 22 performs error diffusion on the lower 2 bits of the 8-bit video signal input from the first noise shaping unit 21 by noise shaping processing, and converts it to a 6-bit video signal. Output. As a result, in the 6-bit video signal output from the second noise shaping unit 22, the lower 4 bits of the input video signal VS are substantially diffused by two-stage noise shaping. The video signal output from the second noise shaping unit 22 is input to the third noise shaping unit 23 and is converted into a 10-bit video signal by adding “0000” to the lower 4 bits in the bit number conversion unit 15. Then, the signal is input to the signal selector 4.

Further, the third noise shaping unit 23 performs error diffusion on the lower 2 bits of the 6-bit video signal input from the second noise shaping unit 22 by noise shaping processing, and converts it into a 4-bit video signal. Output. As a result, the lower 6 bits of the input video signal VS are substantially diffused in the 4-bit video signal output from the third noise shaping unit 23 by the three-stage noise shaping. The video signal output from the third noise shaping unit 23 is converted to a 10-bit video signal by adding “000000” to the lower 6 bits in the bit number conversion unit 16 and then input to the signal selection unit 4. The

Also in the liquid crystal display device 20 shown in FIG. 5, as in the liquid crystal display device 10 shown in FIG. 1, the signal selection unit 4 has no noise shaping effect, the noise shaping effect is small (low-order 2 bits of the video signal are diffused), and noise. It is possible to switch between four levels during the shaping effect (diffusion of the lower 4 bits of the video signal) and the large noise shaping effect (diffusion of the lower 6 bits of the video signal). The switching operation of the noise shaping effect is the same as that of the liquid crystal display device 10 shown in FIG. 1, and the description thereof is omitted here. Also in the liquid crystal display device 20 shown in FIG. 5, the generation of pseudo contours can be effectively reduced as in the liquid crystal display device 10 shown in FIG. 1.

The liquid crystal display device 20 in which a plurality of noise shaping units are connected in series can have a smaller circuit configuration of the noise shaping unit than the liquid crystal display device 10 in which a plurality of noise shaping units are connected in parallel. That is, in the liquid crystal display device 10 of FIG. 1, each of the first to third noise shaping units 11, 12, and 13 has a 10-bit input video signal VS as a processing target. On the other hand, in the liquid crystal display device 20 of FIG. 5, only the first noise shaping unit 21 processes the 10-bit input video signal VS, and the second and third noise shaping units 22 and 23 are 8 bits smaller than 10 bits. Since the 6-bit input video signal VS is a processing target, the circuit configuration can be reduced in size.

On the other hand, in the liquid crystal display device 20 in which a plurality of noise shaping units are connected in series, it is necessary to design a circuit so that moire does not occur due to accumulation of noise shaping effects in a plurality of stages. In this respect, in the liquid crystal display device 10 in which a plurality of noise shaping units are connected in parallel, the moire due to the accumulation of the noise shaping effect as described above does not occur, and thus the circuit design is easy.

The liquid crystal display devices 10 and 20 of the present embodiment shown in FIGS. 1 and 5 are configured to diffuse the lower 2 bits, lower 4 bits and lower 6 bits of the video signal by the first to third noise shaping units. However, the present invention is not limited to this, and the number of error diffusion bits for determining the degree of the noise shaping effect can be arbitrarily set. For example, the first to third noise shaping units diffuse the lower 2 bits of the video signal (noise shaping 10 → 8 bits), diffuse the lower 3 bits (noise shaping 10 → 7 bits), and diffuse the lower 4 bits, respectively. The configuration may be (noise shaping 10 → 6 bits).

In addition, the liquid crystal display devices 10 and 20 of the present embodiment shown in FIGS. 1 and 5 are configured to be able to switch the noise shaping effect in four stages with respect to four contrast gain ranges. It is not limited. That is, in the present embodiment, the generation of pseudo contours can be effectively reduced if the configuration can switch the noise shaping effect in n stages for n (n is an integer of 2 or more) contrast gain ranges. Has an effect. More specifically, (n−1) noise shaping units having different noise shaping effects are connected in parallel or in series, and the contrast gain calculation unit 2 divides the region into n regions according to the contrast gain applied to the video signal VS. Any configuration that switches the noise shaping effect (depending on which of the contrast gain ranges has been assigned) provides the effects of the present embodiment.

Next, a configuration capable of further reducing the pseudo contour by gradually switching the noise shaping effect using the α blend process in the pixel region at the boundary where the noise shaping effect is switched will be described below.

FIG. 6 is a schematic configuration diagram in which the α blend process is applied to the liquid crystal display device 10 of FIG. The liquid crystal display device 10 further includes a delay unit 5, a signal selection unit 6, a change detection unit 7, a coefficient switching unit 8, and an α blend unit 9 in addition to the configuration of FIG. 1.

The selection control signal SC from the contrast gain calculation unit 2 is input to the delay unit 5. The delay unit 5 delays the selection control signal SC for a period corresponding to horizontal N pixels (N is a natural number) and outputs the delayed selection control signal SC to the signal selection unit 6. That is, when the period of the horizontal synchronizing signal of the video signal VS is T [seconds], the delay unit 5 delays the selection control signal SC by N × T [seconds]. Here, the “horizontal N pixels” to be delayed corresponds to a boundary pixel region Ndot where the noise shaping effect is gradually switched by the α blending process, as shown in FIG.

The configuration of the signal selection unit 6 is a four-input multiplexer similar to that of the signal selection unit 4, and is output from the contrast gain adjustment unit 3 to each input terminal of the signal selection unit 6 (no noise shaping process is performed). The video signal VS and the video signal VS that has been subjected to the noise shaping processing by the first to third noise shaping units 11, 12, and 13 are input. Since the selection control signal SC delayed by horizontal N pixels is input to the signal selection unit 6 as described above, the output of the signal selection unit 6 (see (e) in FIG. 7) is the signal selection unit 4. (See (d) in FIG. 7) is delayed by the horizontal N pixels.

The change control unit 7 receives the selection control signal SC from the contrast gain calculation unit 2. Then, the change detecting unit 7 detects the boundary at which the noise shaping effect is switched by detecting the timing at which the selection control signal SC changes, and outputs the detection signal to the coefficient switching unit 8.

When the detection signal is input from the change detection unit 7, the coefficient switching unit 8 gradually increases the value of the coefficient α of the α blending process from 0 to 1 over a period corresponding to the boundary pixel region Ndot where the noise shaping effect is switched. , And output to the α blend unit 9 (see (f) in FIG. 7). The coefficient switching unit 8 sets the coefficient α to 0 except during a period corresponding to horizontal N pixels. For example, when the detection signal is input from the change detection unit 7, the coefficient switching unit 8 increments the counter value from 0 to 1 for each period T of the horizontal synchronization signal of the video signal VS, In conjunction with a counter that resets to 0 when the value reaches N, the value of the coefficient α can be increased by (1 / N) every period T.

The α blend unit 9 includes a video signal VS (referred to as a video signal A) output from the signal selection unit 4, a video signal VS (referred to as a video signal B) output from the signal selection unit 6, and a coefficient switching unit 8. The value of the coefficient α to be output is input. The α blend unit 9 semi-transparently combines the above two image signals A and B using the coefficient α as shown in the following expression (1) to generate a video signal OUT.

OUT = (1-α) × A + α × B (1)

The video signal output from the α blend unit 9 is input to the drive circuit 17 in FIG. 1, and an image corresponding to the video signal is displayed on the liquid crystal panel 18.

The operation of gradually switching the noise shaping effect using the α blend process in the above configuration will be described below with reference to FIG. Here, the case where the video signal noise-shaped by the first noise shaping unit 11 is switched to the video signal noise-shaped by the second noise shaping unit 12 is illustrated.

As shown in (c) of FIG. 7, when the selection control signal SC output from the contrast gain calculation unit 2 is switched from “01” to “10”, the video signal output from the signal selection unit 4. In A, the noise shaping effect is switched at the change timing of the selection control signal SC as shown in FIG. In the figure, the pixel region of the video signal noise-shaped by the first noise shaping unit 11 is “NS8 bit region”, and the pixel region of the video signal noise-shaped by the second noise shaping unit 12 is “NS6 bit region”. ".

On the other hand, the video signal B output from the signal selection unit 6 is video for a period corresponding to the boundary pixel region Ndot as shown in FIG. 7E due to the delay processing of the selection control signal SC by the delay unit 5. Delayed to signal A, the noise shaping effect is switched.

Then, the value of the coefficient α output from the coefficient switching unit 8 indicates that the change detection unit 7 indicates that the selection control signal SC has been switched from “01” to “10” as shown in (f) in FIG. After the detection, it gradually increases from 0 to 1 over a period corresponding to the boundary pixel region Ndot.

Therefore, by the α blend process in the boundary pixel area Ndot, the “NS6 bit area” of the video signal A gradually increases as shown in (g) of FIG. 7, while the video signal B as shown in (h) of FIG. The “NS8-bit area” of the area gradually decreases. As a result, as shown in (b) of FIG. 7, the “NS8 bit region” and the “NS6 bit region” are gradually α-blended, and the video signal OUT in which the noise shaping effect is gradually switched is output.

For comparison, a video signal in the case where the α blending process is not performed is shown in (a) of FIG. In this case, the noise shaping effect is switched at a stroke between the last pixel of the “NS8 bit region” and the start pixel of the “NS6 bit region”. On the other hand, since the noise shaping effect is gradually switched over the boundary pixel region Ndot by the configuration in which the α blend process is performed, the effect of reducing the pseudo contour is further improved.

Note that a fixed value may be used for the number N of pixels in the boundary pixel region Ndot, but it may be changed as appropriate according to the video signal. For example, a fast-moving image is relatively less blurred than an image that does not move much, so that the pseudo contour is not noticeable. Therefore, it is possible to adjust to reduce the number N of pixels in the boundary pixel region Ndot as the image moves faster. Further, for example, in consideration of human visual characteristics such that the false contour is conspicuous for the skin color and the pseudo contour is not conspicuous for the green color, the number N of pixels in the boundary pixel region Ndot can be adjusted according to the color gamut of the video signal.

FIG. 6 shows an example in which the α blend process is applied to a configuration in which a plurality of noise shaping units (first to third noise shaping units 11, 12, 13) are connected in parallel. The α blend process can also be applied to the configuration shown in FIG. 5 in which a plurality of noise shaping units are connected in series.

(Embodiment 2)
FIG. 8 is a schematic configuration diagram of a liquid crystal display device 40 (video display device) to which the video signal processing device according to the present embodiment is applied. In addition, the same member number is attached to the member which has the structure similar to the said Embodiment 1, and the description is abbreviate | omitted.

In FIG. 8, a liquid crystal display device 40 includes a color gamut detection unit 30 (error diffusion effect switching unit), a signal selection unit 4 (error diffusion effect switching unit), and a first noise shaping unit 11 (error) as video signal processing devices. A diffusion unit), a second noise shaping unit 12 (error diffusion unit), a third noise shaping unit 13 (error diffusion unit), and bit number conversion units 14-16. Furthermore, the liquid crystal display device 40 includes a drive circuit 17 and a liquid crystal panel 18 (display unit).

The color gamut detection unit 30 detects a color gamut based on the hue of the video signal VS, and outputs a selection control signal SC to the signal selection unit 4 according to the detection result. The processing of the color gamut detection unit 30 is performed in real time in synchronization with the video signal VS. The color gamut can be classified into, for example, green, red, gray (achromatic), and blue. In addition, color gamut classifications such as yellow to green, magenta to red, and cyan to blue are possible.

Even if the gradation is the same (that is, the number of bits of the video signal is the same), there are color gamuts where false contours are conspicuous and those that are not so due to human visual characteristics. For example, a false contour is easily noticeable in a blue color gamut, whereas a false contour is relatively inconspicuous in a green color gamut. For example, the pseudo contour is more conspicuous in the order of green system <red system <gray system (achromatic color) <blue system.

Therefore, for example, when the hue of the video signal VS is green, the color gamut detection unit 30 outputs the selection control signal SC = “00”, and the video signal VS not subjected to noise shaping processing is output to the signal selection unit 4. To be selected. Further, the color gamut detection unit 30 outputs the selection control signal SC = “01” when the hue of the video signal VS is red, for example, and the first noise shaping unit 11 performs noise shaping processing (10 → 8 bits). The video signal subjected to is selected by the signal selection unit 4. Further, the color gamut detection unit 30 outputs, for example, a selection control signal SC = “10” when the hue of the video signal VS is gray, and the second noise shaping unit 12 performs noise shaping processing (10 → 6 bits). The video signal subjected to is selected by the signal selection unit 4. The color gamut detection unit 30 outputs the selection control signal SC = “11” when the hue of the video signal VS is blue, for example, and the third noise shaping unit 12 performs noise shaping processing (10 → 4 bits). The video signal subjected to is selected by the signal selection unit 4. As a result, the noise shaping effect becomes higher in the order of green system <red system <gray system <blue system (see FIG. 9).

In the liquid crystal display device 40 configured as described above, the color gamut detection unit 30 detects the color gamut of the video signal VS, and adaptively controls the noise shaping effect according to the color gamut. As a result, for example, in a sky or water surface video signal (a video signal in a blue or cyan to blue color region), a process that enhances the noise shaping effect (increases the number of lower bits diffused by noise shaping) is performed. . In addition, noise shaping processing is not performed on a video signal such as a mountain (video signal in a green color region) (or processing with a very weak noise shaping effect can be performed). As described above, as the noise shaping effect is increased (the number of lower bits diffused by noise shaping is increased), the image is blurred and the generation of pseudo contour can be reduced. By increasing the noise shaping effect for a color gamut that is more conspicuous, the occurrence of pseudo contour can be effectively reduced.

The liquid crystal display device 40 has a configuration in which a plurality of noise shaping units (first to third noise shaping units 11, 12, 13) are connected in parallel. As shown in FIG. It can also be configured as a liquid crystal display device 50 connected in series. Since the configuration in which a plurality of noise shaping units are connected in series has already been described in detail with reference to FIG. 5, the description thereof is omitted here.

The liquid crystal display devices 40 and 50 of the present embodiment shown in FIGS. 8 and 10 are configured to diffuse the lower 2 bits, lower 4 bits and lower 6 bits of the video signal by the first to third noise shaping units. However, the present invention is not limited to this, and the number of error diffusion bits for determining the degree of the noise shaping effect can be arbitrarily set.

In addition, the liquid crystal display devices 40 and 50 according to the present embodiment shown in FIGS. 8 and 10 are configured to be able to switch the noise shaping effect in four stages for four color gamuts, but this is not limitative. Is not to be done. That is, if the configuration can switch the noise shaping effect in n stages for n (n is an integer of 2 or more) color gamuts, the operation of this embodiment can effectively reduce the occurrence of pseudo contours. There is an effect. More specifically, (n−1) noise shaping units having different noise shaping effects are connected in parallel or in series, and the color gamut detection unit 30 has a color gamut corresponding to the hue of the video signal VS (n Any configuration may be used as long as it detects an area-divided color gamut and switches the noise shaping effect according to the color gamut.

Further, the α blend process shown in FIG. 6 can be applied to the liquid crystal display devices 40 and 50 of the present embodiment shown in FIGS. As a result, the noise shaping effect can be gradually switched using the α blend process in the pixel region at the boundary where the noise shaping effect is switched according to the color gamut of the video signal VS, and the pseudo contour can be further reduced. I can plan.

Here, a configuration that combines the effects of the first embodiment and the second embodiment will be described. A liquid crystal display device 60 shown in FIG. 11 includes the color gamut detection unit 30 that detects the color gamut of the video signal VS in addition to the configuration of the liquid crystal display device 10 of FIG. The liquid crystal display device 60 switches the noise shaping effect according to the contrast gain and color gamut of the video signal VS. The switching operation of the noise shaping effect will be described below.

Information on the color gamut detected by the color gamut detection unit 30 is output to the contrast gain calculation unit 2. As described in the first embodiment, the contrast gain calculation unit 2 generates the selection control signal SC that switches the noise shaping effect in four stages according to the contrast gain applied to the video signal VS. At this time, the selection control signal SC is corrected based on the color gamut information from the color gamut detection unit 30.

For example, considering the fact that pseudo contours tend to be conspicuous in the order of green system <red system <gray system <blue system, the noise shaping effect is lowered by two levels if the color gamut is green, and the effect is achieved if the color gamut is red. It is conceivable to increase the effect by one step if the color gamut is gray, and to increase the effect by two steps if the color gamut is blue.

Here, a case where a contrast gain is adjusted by a gamma curve as shown in FIG. 3 for an input video signal VS having a dynamic range as shown in FIG. 2 is considered as a specific example. At this time, the contrast gain calculation unit 2 selects the selection control signal so that the noise shaping effect becomes the highest during the period in which the video signal VS in the luminance region multiplied by the double gain is output from the contrast gain adjustment unit 3. The SC is set to “11” in the first embodiment. For example, when the color gamut of the luminance region is green, the noise shaping effect is reduced by two steps by incorporating the elements of the second embodiment. The control signal SC is set to “01”. In the above-described step correction based on the color gamut information, if the noise shaping effect that can be selected reaches the upper limit or the lower limit, and the step correction of the effect cannot be further performed, the upper limit or the lower limit of the noise shaping effect is selected. Will be.

Thereby, it is possible to select an optimal noise shaping effect considering both the contrast gain and the color gamut of the video signal VS, and it is possible to more effectively suppress the occurrence of pseudo contours and improve the video quality.

As another configuration example in which the contrast gain calculation unit 2 corrects the selection control signal SC based on the color gamut information from the color gamut detection unit 30, the contrast gain value when selecting the noise shaping effect is set to the color gamut. It is conceivable to multiply the corresponding correction coefficient γ. Here, in consideration of the fact that pseudo contours are more conspicuous in the order of green system <red system <gray system <blue system, for each of these correction coefficients γ, γ _Green <γ _Red <1 <γ _Gray <γ It can be set like _Blue . When the color gamut of the video signal VS in the luminance region to which the gain of 2 is applied as in the specific example is green, for example, γ _Green = 0.7 and the corrected contrast gain value is 2 The noise shaping effect is selected by setting xγ _Green = 1.4 times. In this case as well, the noise shaping effect is reduced by two stages, and “01” is selected as the selection control signal SC.

Also in the liquid crystal display device 60 shown in FIG. 11, a plurality of noise shaping units may be connected in series as shown in FIG. 5, or the α blend process shown in FIG. 6 may be applied.

In each of the above-described embodiments, examples in which the first to third noise shaping units are applied as error diffusion units that perform error diffusion on the video signal VS have been described. However, the present invention is not limited to this. For example, the error diffusion unit may perform error diffusion other than noise shaping such as dithering.

In each of the above embodiments, a liquid crystal display device has been described as an example of a video display device. However, the video display device to which the present invention is applied is not limited to this. For example, the present invention can be similarly applied to other video display devices such as a plasma display and an organic EL (electroluminescence) display.

The specific embodiments described above mainly include inventions having the following configurations.

A video signal processing apparatus according to an aspect of the present invention includes a contrast gain adjusting unit that adjusts a contrast gain of a video signal, and error diffusion that performs error diffusion on the video signal whose contrast gain is adjusted by the contrast gain adjusting unit. And an error diffusion effect switching unit that switches the error diffusion effect by changing the number of bits that the error diffusion unit diffuses as an error according to the contrast gain of the video signal.

According to the above configuration, the contrast gain of the video signal is adjusted by the contrast gain adjustment unit. At this time, the larger the gain applied to the video signal, the larger the gradation difference and the more likely the pseudo contour is generated. Therefore, in the present invention, error diffusion processing is performed by the error diffusion unit on the video signal whose contrast gain has been adjusted. In this error diffusion process, the error diffusion effect switching unit switches the error diffusion effect by changing the number of bits for error diffusion according to the contrast gain of the video signal. As described above, the generation of the pseudo contour can be controlled by adaptively switching the error diffusion effect (changing the number of bits for error diffusion) according to the contrast gain. This is because as the error diffusion effect is increased (the number of bits for error diffusion is increased), the video is blurred and the pseudo contour is reduced. According to the configuration of the present invention, it is possible to enhance the error diffusion effect for a video signal having a large contrast gain. Therefore, it is possible to improve the video quality by suppressing the generation of pseudo contours.

In the video signal processing apparatus, the error diffusion unit includes a noise shaping unit that diffuses noise shaping using lower bits of the video signal as errors, and the error diffusion effect switching unit has a contrast gain of the video signal. It is preferable to increase the number of lower bits diffused by the noise shaping unit as the value increases.

In this way, the noise shaping unit is used for error diffusion processing, and as the contrast gain of the video signal increases, the number of lower bits to be diffused increases, thereby effectively reducing the occurrence of pseudo contours with a simple configuration. it can.

Further, in the above video signal processing apparatus, an α blend processing unit that gradually switches the error diffusion effect by α blend processing of video signals having different error diffusion effects with respect to the video signal of the boundary pixel region where the error diffusion effect switches. Is preferably further provided.

With the above configuration, in the boundary pixel region where the error diffusion effect is switched, the error diffusion effect is not switched all at once, but the error diffusion effect is gradually switched while α-blending video signals having different error diffusion effects. Become. Thereby, the gradation in the boundary pixel region is improved, and the effect of reducing the pseudo contour is further improved.

The video signal processing apparatus further includes a color gamut detection unit that detects a color gamut of the video signal, and the error diffusion effect switching unit is configured to detect the error according to a contrast gain and a color gamut of the video signal. It is preferable to switch the error diffusion effect by changing the number of bits that the diffusion unit diffuses as an error.

With the above configuration, it is possible to realize selection of the optimum error diffusion effect considering both the contrast gain and the color gamut of the video signal, and it is possible to more effectively suppress the generation of pseudo contours.

A video signal processing apparatus according to another aspect of the present invention includes a color gamut detection unit that detects a color gamut of a video signal, an error diffusion unit that performs error diffusion on the video signal, and the color gamut detection unit detects And an error diffusion effect switching unit that switches the error diffusion effect by changing the number of bits that the error diffusion unit diffuses as an error according to the color gamut.

According to the above configuration, the error diffusion effect is adaptively switched according to the color gamut of the video signal (the number of bits for error diffusion is changed). Here, regarding the color gamut, even if the gradation is the same (that is, the number of bits of the video signal is the same), there are a color gamut in which false contours are conspicuous and a color gamut in which it is not so (for example, The blue color gamut is relatively more prominent in pseudo contour than the green color gamut). Further, as described above, as the error diffusion effect is increased (the number of bits for error diffusion is increased), the video is blurred and the pseudo contour can be reduced. Therefore, according to the configuration of the present invention, if the error diffusion effect is enhanced in a color gamut in which pseudo contour is more conspicuous, generation of pseudo contour can be suppressed and image quality can be improved.

Further, in the video signal processing device, the error diffusion unit includes a noise shaping unit that diffuses the low-order bits of the video signal as an error by noise shaping, and the error diffusion effect switching unit has a color gamut in which pseudo contour is conspicuous. It is preferable to increase the number of lower bits diffused by the noise shaping unit.

In this way, the noise shaping unit is used for error diffusion processing, and as the contrast gain of the video signal increases, the number of lower bits to be diffused increases, thereby effectively reducing the occurrence of pseudo contours with a simple configuration. it can.

In addition, it is preferable that the video signal processing apparatus further includes an α blend processing unit that gradually switches the error diffusion effect by α blend processing on the video signal in the boundary pixel region where the error diffusion effect is switched.

With the above configuration, in the boundary pixel region where the error diffusion effect is switched, the error diffusion effect is not switched all at once, but the error diffusion effect is gradually switched while α-blending video signals having different error diffusion effects. Become. Thereby, the gradation in the boundary pixel region is improved, and the effect of reducing the pseudo contour is further improved.

A video display device according to still another aspect of the present invention includes the video signal processing device described above and a display unit that displays a video signal that has been subjected to signal processing by the video signal processing device.

With the above configuration, it is possible to realize a video display device capable of effectively suppressing the occurrence of pseudo contours and improving the video quality.

The video signal processing device and the video display device according to the present invention can be suitably used for video equipment such as a television receiver, a display device, and a projector device.

Claims (8)

1. A contrast gain adjustment unit for adjusting the contrast gain of the video signal;
   An error diffusion unit for performing error diffusion on the video signal whose contrast gain has been adjusted by the contrast gain adjustment unit;
   An image signal processing apparatus comprising: an error diffusion effect switching unit that switches an error diffusion effect by changing a number of bits that the error diffusion unit diffuses as an error according to a contrast gain of the image signal.
2. The error diffusion unit includes a noise shaping unit for diffusing by noise shaping as a lower bit of the video signal as an error,
   The video signal processing apparatus according to claim 1, wherein the error diffusion effect switching unit increases the number of lower bits diffused by the noise shaping unit as the contrast gain of the video signal increases.
3. An α blend processing unit that gradually switches the error diffusion effect by α blend processing of video signals having different error diffusion effects with respect to the video signal in the boundary pixel region where the error diffusion effect is switched is further provided. The video signal processing apparatus according to claim 1 or 2.
4. A color gamut detector that detects a color gamut of the video signal;
   The error diffusion effect switching unit switches the error diffusion effect by changing the number of bits that the error diffusion unit diffuses as an error according to a contrast gain and a color gamut of the video signal. 4. The video signal processing apparatus according to any one of items 3 to 3.
5. A color gamut detector that detects the color gamut of the video signal;
   An error diffusion unit for performing error diffusion on the video signal;
   An error diffusion effect switching unit that switches an error diffusion effect by changing the number of bits that the error diffusion unit diffuses as an error according to the color gamut detected by the color gamut detection unit. Signal processing device.
6. The error diffusion unit includes a noise shaping unit for diffusing by noise shaping as a lower bit of the video signal as an error,
   6. The video signal processing apparatus according to claim 5, wherein the error diffusion effect switching unit increases the number of lower bits diffused by the noise shaping unit in a color gamut in which pseudo contour is more conspicuous.
7. 7. The video according to claim 5, further comprising an α blend processing unit that gradually switches the error diffusion effect by α blend processing with respect to the video signal of the boundary pixel region where the error diffusion effect is switched. Signal processing device.
8. A video signal processing device according to any one of claims 1 to 7,
   And a display unit that displays the video signal that has been signal-processed by the video signal processing device.

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