JP7557298B2 - Video encoding device, video decoding device, and programs thereof - Google Patents

Description

The present invention relates to a video encoding device, a video decoding device, and programs for compressing and transmitting wide color gamut video.

In recent years, wide color gamut images that can reproduce more vivid colors than conventional color gamut images such as ITU-R Recommendation BT.709 have become increasingly popular. For example, the color gamut specified in ITU-R Recommendation BT.2020 is used for 8K/4K broadcasting, and the area ratio on the xy chromaticity diagram of the color gamut that can be reproduced by BT.2020 is about 1.5 times that of BT.709 used in 2K broadcasting.

Figure 6 shows the xy chromaticity diagram of the CIE XYZ color system for ITU-R Recommendations BT. 709 and BT. 2020. In Figure 6, the area surrounded by the dotted line is the range of colors that can be seen by the naked eye. The color gamut of BT. 709 and BT. 2020 is expressed as a triangle connecting the vertex coordinates of each color RGB (note that the white point W according to the CIE standard illuminant D65 is also an achromatic point). In addition, since colors beyond the color gamut of the triangle cannot be reproduced in images conforming to the BT. 709 and BT. 2020 standards, the color reproduction on the video decoding device side can be improved by widening the color gamut of the images compressed and transmitted by the video encoding device. In addition, by combining it with HDR (High Dynamic Range) technology that can express a wide range of brightness, it is possible to express realistic images.

Incidentally, when a video encoding device compresses and transmits a video frame signal consisting of a luminance signal and a color difference signal, processing is carried out taking into consideration the fact that human vision is sensitive to degradation of the luminance signal that contributes to contour information, but insensitive to degradation of the color difference signal that contributes to color information. For example, a color image captured by a camera is composed of three components, R, G, and B, which are the three primary colors of light, but when input to a video encoding device, it is converted into three components, a luminance signal Y and color difference signals Cb and Cr, and a subsampling process is carried out to thin out the color difference signals (for example, see Non-Patent Document 1).

The aforementioned 8K/4K broadcasting uses a 4:2:0 video format, in which the number of horizontal and vertical pixels for the color difference signal is half that of the luminance signal. Furthermore, the video encoding device performs processing to reduce the amount of code by making the QP (Quantization Parameter: quantization step value) and quantization matrix coefficients for the color difference signal larger than those for the luminance signal and lowering the reproducibility of the color difference signal.

Edited by Eiichiro Okubo, "H.265/HEVC Textbook", First Edition, Impress Japan, published on October 21, 2013

As mentioned above, by expanding the color gamut of the video compressed and transmitted by the video encoding device, color reproduction on the video decoding device side can be improved. On the other hand, the video encoding device performs processing that takes into account the fact that human vision is sensitive to degradation of the luminance signal that contributes to contour information, and insensitive to degradation of the color difference signal that contributes to color information.

However, when encoding wide color gamut video conforming to the BT.2020 standard at a high compression rate using a video encoding device, there is a problem that reducing the amount of code for the color difference signal as in the past may result in a decrease in subjective quality. In other words, even for images with complex patterns in which degradation of the luminance signal is highly noticeable, the subjective quality may improve if a color difference signal with less degradation is combined, and this has been confirmed experimentally.

Therefore, in consideration of the above problems, the object of the present invention is to provide a video encoding device, a video decoding device, and programs therefor that improve the subjective quality when compressing wide color gamut video.

The video coding device of the present invention is a video coding device that codes a video frame consisting of a luminance signal and a color difference signal, and includes a video coding unit that codes the luminance signal and the color difference signal individually for each predetermined block of the video frame, and a coding control unit that variably controls coding parameters to control the video coding unit, wherein the coding control unit has a function of predicting whether deterioration of the luminance signal of a predetermined block to be coded will be large, and if the coding control unit predicts that the deterioration will be large, controlling the video coding unit to increase the reproducibility of the color difference signal , and if the coding control unit predicts that the deterioration will be large, further determining whether the color difference signal of the predetermined block to be coded of the video frame is within a predetermined range from achromatic, and if it is determined that the color difference signal is within the predetermined range from achromatic, treating the color difference signal as achromatic, and determining coding parameters to completely achromatize the color difference signal, or controlling the auxiliary information to include meta information instructing the color difference signal to be achromatized so that it can be transmitted to the video decoding device .

In addition, in the video encoding device of the present invention, the encoding control unit is characterized by having a function of determining whether the color difference signal is within a predetermined range of high perceptibility when the color difference signal is not within a predetermined range from achromatic color, and determining the encoding parameters of the color difference signal based on the determination result.

Furthermore, the video decoding device of the present invention is a video decoding device that inputs and decodes a video encoding signal of a video frame encoded by the video encoding device of the present invention, and includes a video decoding unit that performs a decoding process on the video encoding signal using encoding parameters based on auxiliary information transmitted from the video encoding device, and a decoding control unit that controls the video decoding unit to perform a decoding process on the video encoding signal based on the auxiliary information transmitted from the video encoding device, and is characterized in that, when meta information instructing the chrominance signal in the block to be decoded to be achromatized is transmitted as the auxiliary information, the decoding control unit controls the video decoding unit by changing the encoding parameters so as to completely achromatize the chrominance signal of the specified block.

Furthermore, the program according to the present invention is configured as a program for causing a computer to function as the video encoding device of the present invention.

Furthermore, the program according to the present invention is configured as a program for causing a computer to function as the video decoding device of the present invention.

The present invention makes it possible to improve the subjective quality when compressing and transmitting wide color gamut video.

1 is a block diagram showing a schematic configuration of a video encoding device according to an embodiment of the present invention. 1 is a block diagram showing a schematic configuration of an encoding control unit in a video encoding device according to an embodiment of the present invention. 4 is a flowchart showing encoding control in the first embodiment by an encoding control unit according to the present invention. 10 is a flowchart showing encoding control in a second embodiment by an encoding control unit according to the present invention. FIG. 1 is a block diagram showing a schematic configuration of a video decoding device according to an embodiment of the present invention. FIG. 1 is a diagram showing an xy chromaticity diagram of the CIE XYZ color system according to ITU-R Recommendations BT.709, BT.2020.

The following describes a video encoding device 1 and a video decoding device 2 according to an embodiment of the present invention, with reference to the drawings.

[Video Encoding Device]
(Overall composition)
1 is a block diagram showing a schematic configuration of a video encoding device 1 according to an embodiment of the present invention. The video encoding device 1 of this embodiment receives a video frame signal consisting of a luminance signal and a color difference signal constituting a frame to be processed, and encodes the luminance signal and the color difference signal individually in a predetermined unit. Typically, the predetermined unit is a block unit, and the encoding process is usually performed by hierarchically subdividing the signal into a GOP (Group of Picture) unit consisting of a plurality of frames, a frame unit, a slice unit which is a divided area within a frame, a tile unit, and a block unit which is a divided area within a frame, slice, and tile. Therefore, the video encoding device 1 of this embodiment will be described as processing the video frame signal from the luminance signal and the color difference signal in a "predetermined block unit".

More specifically, the video encoding device 1 of this embodiment includes an encoding control unit 11 and a video encoding unit 12.

The encoding control unit 11 controls the video encoding unit 12 to encode the luminance signal and the color difference signal individually in a predetermined block unit for a video frame signal consisting of a luminance signal and a color difference signal. In particular, although a detailed embodiment will be described later, the encoding control unit 11 according to the present invention judges the deterioration prediction of the luminance signal based on either one or both of a predetermined complexity obtained from a predetermined encoding result for the luminance signal and a predetermined judgment parameter, determines the encoding parameters for the color difference signal based on the judgment result of the deterioration prediction of the luminance signal, and outputs them to the video encoding unit 12 for control. In addition, the encoding control unit 11 outputs each encoding parameter of the video encoding unit 12 for the luminance signal and the color difference signal to the outside as auxiliary information of the video encoding signal as necessary. This auxiliary information may be transmitted to the video decoding device 2 side in a bit stream that has been entropy-encoded so as to be multiplexed on the bit stream of the video encoding signal, or may be transmitted in a form in which the transmission format or transmission path is changed, such as in a different file format.

The video encoding unit 12 is a processing unit controlled by the encoding control unit 11, which inputs video frames of a moving image consisting of a luminance signal and a color difference signal, and encodes the video frames using block-based encoding such as H.265/HEVC based on encoding parameters. As a typical example, the video encoding unit 12 includes a preprocessing unit 121, a subtraction unit 122, an orthogonal transformation unit 123, a quantization unit 124, an inverse quantization and inverse orthogonal transformation unit 125, an addition unit 126, an intra-screen prediction unit 127, a loop filter 128, an inter-screen prediction unit 129, a switching unit 130, an entropy encoding unit 131, and an output unit 132.

The pre-processing unit 121 inputs a video frame of a video image to be processed, and performs all pre-processing required to generate a second coded signal, such as the coding type (intra-screen coding, inter-screen coding), coding order, prediction reference relationship, coding block as a coding unit, or slice, based on the coding parameters, and outputs the original signal of a predetermined block unit set for each luminance signal and color difference signal to the subtraction unit 122.

The subtraction unit 122 forms a differential signal by subtracting the original signal of a predetermined block unit obtained from the preprocessing unit 121 from the corresponding block unit predicted signal obtained from the switching unit 130 for each luminance signal and color difference signal, and outputs the differential signal to the orthogonal transformation unit 123.

The orthogonal transform unit 123 performs frequency transformation on the difference signal obtained from the subtraction unit 122 based on the orthogonal transform coefficients, and outputs the result to the quantization unit 124.

The quantization unit 124 performs quantization processing on the orthogonal transform coefficient signal obtained from the orthogonal transform unit 123, and outputs the signal to the entropy coding unit 131 and the inverse quantization and inverse orthogonal transform unit 125.

The inverse quantization and inverse orthogonal transform unit 125 performs the inverse processing of the quantization unit 124 on the quantized values of the orthogonal transform coefficient signals obtained from the quantization unit 124 to restore the orthogonal transform coefficient signals, and further performs the inverse processing of the orthogonal transform unit 123 on the orthogonal transform coefficient signals to restore the difference signal, which is output to the addition unit 126.

The adder 126 adds the difference signal obtained from the inverse quantization and inverse orthogonal transformation unit 125 to the prediction signal obtained from the switching unit 130 to generate a locally decoded block, which it outputs to the intra-screen prediction unit 127 during intra-coding, and to the inter-screen prediction unit 129 via the loop filter 128 during inter-coding.

During intra-coding, the intra-screen prediction unit 127 temporarily stores the locally decoded block obtained from the adder unit 126 as an adjacent block of the next block to be coded, generates a prediction signal of the next block to be coded based on the adjacent block, and outputs it to the subtraction unit 122 and the adder unit 126 via the switching unit 130.

The loop filter 128 is a processing unit that applies a so-called deblocking filter, a band-pass filter, and SAO (Sample Adaptive Offset), which performs offset processing on a block-by-block basis, to the locally decoded block obtained from the addition unit 126.

During inter-coding, the inter-screen prediction unit 129 temporarily stores the locally decoded blocks obtained from the loop filter 128 on a picture-by-picture basis, generates a prediction signal for the next block to be coded based on block matching in the reference picture referenced as motion prediction, and outputs the signal to the subtraction unit 122 and the addition unit 126 via the switching unit 130.

The switching unit 130 is a functional unit that switches between intra-coding and inter-coding depending on the coding type.

The entropy coding unit 131 performs entropy coding processing on the quantized values of the orthogonal transform coefficient signal obtained from the quantization unit 124 to generate a video coding signal for the luminance signal and the color difference signal, and outputs the video coding signal to the output unit 132 in the form of a bit stream.

The output unit 132 outputs the video encoded signal generated by the entropy encoding unit 131 to the outside in the form of a bit stream. In addition to the form of outputting the video encoded signal generated by one-time (one-pass) encoding to the outside, the output unit 132 can also output the video encoded signal generated by performing multi-pass encoding processing to the outside, according to an output control signal from the encoding control unit 11. In multi-pass encoding, when encoding a video frame by block-based encoding, the video frame is once encoded and analyzed using a simple known method, and the encoding processing is performed after grasping the overall picture. In consideration of processing delay and energy efficiency, two-pass encoding is often used.

(Configuration of the encoding control unit)
Fig. 2 is a block diagram showing a schematic configuration of the encoding control unit 11 in the video encoding device 1 according to an embodiment of the present invention. The encoding control unit 11 shown in Fig. 2 includes a pre-measurement unit 111, a luminance encoding parameter determination unit 112, an encoding parameter setting unit 113, a luminance complexity determination unit 114, a luminance degradation prediction determination unit 115, a color difference encoding parameter determination unit 116, an output control unit 117, and a determination result storage unit 118. Note that the configuration example of the encoding control unit 11 shown in Fig. 2 is a configuration example having functional units when all of the encoding controls of the embodiments according to Figs. 3 and 4 described later can be realized, and it is not necessary to have all of those functional units.

The pre-measurement unit 111 inputs a video frame of the moving image to be coded this time, and instructs the luminance coding parameter determination unit 112 to determine arbitrarily determined coding parameters related to the luminance signal. The pre-measurement unit 111 also pre-measures the complexity related to the luminance signal based on predetermined criteria that include at least an analysis of the variance value or frequency of the luminance signal, and outputs the result to the luminance complexity determination unit 114. Note that when the pre-measurement unit 111 is configured not to pre-measure the complexity related to the luminance signal, this pre-measurement process can be omitted.

The luminance coding parameter determination unit 112 determines coding parameters for the luminance signal based on an arbitrary criterion (for example, determines coding parameters for the luminance signal that are prepared in advance and are deemed suitable for a large number of moving images) based on instructions from the pre-measurement unit 111, and outputs the determined coding parameters to the coding parameter setting unit 113.

The luminance complexity determination unit 114 determines the complexity of the luminance signal based on a predetermined determination criterion including at least one of the analysis of the PSNR (Peak Signal-to-Noise Ratio), SSIM (Structural SIMilarity index), and the value obtained by multiplying QP and the code amount of the encoding result of the luminance signal of the immediately preceding video frame (the encoding result of the immediately preceding video frame or the encoding result of the first pass in two-pass encoding). In addition, when the luminance complexity determination unit 114 obtains the determination result of the complexity of the luminance signal from the advance measurement unit 111, the luminance complexity determination unit 114 may omit the complexity determination process based on the encoding result of the luminance signal obtained from the video encoding unit 12, or may determine the complexity of the luminance signal by a comprehensive determination that takes into account both and is weighted in advance. Then, the luminance complexity determination unit 114 outputs the determined complexity of the luminance signal to the luminance degradation prediction determination unit 115.

The luminance degradation prediction determination unit 115 performs a luminance degradation prediction determination based on either or both of the complexity of the luminance signal obtained from the luminance complexity determination unit 114 and a determination parameter input in advance (a setting related to the bit rate for the video format of the video frame, or an instruction to take into account the degradation prediction history of the reference block related to the motion compensation prediction). Then, when the luminance degradation prediction determination unit 115 determines whether or not the degradation of the luminance signal of the block to be coded is predicted to be large, it outputs the determination result to the chrominance coding parameter decision unit 116.

It can be estimated that luminance signal degradation will occur when the complexity of the luminance signal is high, and furthermore, it can be estimated that luminance signal degradation will occur from the bit rate settings for the video format of the video frame. The judgment result of the luminance signal degradation prediction is temporarily stored in the judgment result storage unit 118 at least for the period of the GOP. As a result, when it has been judged that luminance signal degradation is predicted to be large as the history of the reference block related to the motion compensation prediction referenced by the encoding target block, the luminance degradation prediction judgment unit 115 can use this to judge that luminance signal degradation is also predicted to be large for the encoding target block.

The color difference encoding parameter determination unit 116 determines whether to increase or decrease the reproducibility of the color difference signal based on the result of the degradation prediction of the luminance signal obtained from the luminance degradation prediction determination unit 115, determines the encoding parameters of the color difference signal corresponding to the determined reproducibility, and outputs them to the encoding parameter setting unit 113.

The color difference coding parameter determination unit 116 can also have a function of predicting whether the deterioration of the luminance signal will be large, and if it predicts that the deterioration will be large, determining whether the color difference signal of the block to be coded is close to achromatic (whether it is within a predetermined range from achromatic), determining whether the color difference signal is close to achromatic (whether it is within a predetermined range from achromatic) for the color difference signal of the block to be coded, determining whether the color difference signal is achromatic and determining coding parameters to completely achromatize the color difference signal if the color difference signal is close to achromatic (within a predetermined range from achromatic), or controlling the output control unit 117 to include meta information in the auxiliary information to make it achromatic and transmit it to the video decoding device 2 side, and determining whether the color difference signal is within a predetermined range of high perceptibility if the color difference signal is not within a predetermined range from achromatic, and determining coding parameters for the color difference signal based on the determination result.

Then, the coding parameter setting unit 113 sets the coding parameters for the luminance signal determined by the luminance coding parameter determination unit 112 and the coding parameters for the chrominance signal determined by the chrominance coding parameter determination unit 116 in the video coding unit 12, and outputs a notification of this to the output control unit 117.

After setting each encoding parameter in the video encoding unit 12 for the luminance signal and the color difference signal, the output control unit 117 outputs each encoding parameter as auxiliary information of the video encoding signal as necessary so as to be transmittable to the video decoding device 2. The output control unit 117 also transmits an output control signal to the output unit 132 in the video encoding unit 12, and controls the video encoding signal generated by the entropy encoding unit 131 to be outputted to the outside in the form of a bit stream so as to be transmittable to the video decoding device 2. As described above, the output unit 132 can output a video encoding signal generated by performing two-pass encoding processing to the outside, in addition to outputting a video encoding signal generated by one-time (one-pass) encoding to the outside, according to the output control signal from the encoding control unit 11.

(Encoding control in the first embodiment)
FIG. 3 is a flowchart showing the encoding control of the encoding control unit 11 according to the first embodiment of the present invention.

First, the encoding control unit 11 uses the functions of the advance measurement unit 111, the luminance encoding parameter determination unit 112, the luminance complexity determination unit 114, and the luminance degradation prediction determination unit 115 to determine whether or not significant degradation of the luminance signal is expected in a specific block to be encoded when performing block-based encoding of the video frame to be encoded this time of the moving image (step S1).

More specifically, in step S1, when performing block-based encoding of a video frame of a moving image to be encoded this time, the encoding control unit 11 performs a degradation prediction judgment process to judge whether or not the luminance signal of the block to be encoded is predicted to be significantly deteriorated based on a predetermined complexity obtained from a pre-measurement result of the current video frame to be processed, a predetermined complexity obtained from the encoding result of the immediately preceding video frame or the encoding result of the first pass in a specified two-pass encoding, and one or more of judgment parameters input in advance.

The deterioration prediction judgment using the complexity uses one or more of the following judgment criteria (A1) to (A5). When multiple judgment criteria are used, a weighted overall judgment is made.
(A1) The PSNR of the encoding result of the immediately preceding video frame or the encoding result of the first pass in two-pass encoding is equal to or lower than a predetermined value.
(A2) The SSIM of the encoding result of the immediately preceding video frame or the encoding result of the first pass in two-pass encoding is equal to or less than a predetermined value.
(A3) The product of the QP of the encoding result of the immediately preceding video frame or the encoding result of the first pass in two-pass encoding and the code amount (output of the video encoding device) is equal to or greater than a predetermined value.
(A4) The variance value of the luminance signal of the current video frame to be processed, which is measured in advance, is equal to or greater than a predetermined value.
(A5) The variance value after frequency conversion of the luminance signal of the current video frame to be processed, which is measured in advance, is equal to or larger than a predetermined value.

In addition, the deterioration prediction judgment based on the coding parameters used as the judgment parameters input in advance shall use one or more of the following judgment criteria (B1) to (B3), and when multiple judgment criteria are used, a pre-weighted overall judgment shall be made.
(B1) The fixed bit rate setting value for the video format of the current video frame to be processed is equal to or lower than a predetermined value (the variance value of the luminance signal of the current video frame has been measured in advance, and when the fixed bit rate setting value set for transmission convenience is equal to or lower than a predetermined value, it is pre-set as being of high complexity).
(B2) The target bit rate when performing bit rate control on the video format of the current video frame to be processed is below a predetermined value (the variance value of the luminance signal of the current video frame has been measured in advance, and when the bit rate target value of the bit rate control used for transmission purposes is below a predetermined value, the complexity is pre-set as high).
(B3) When a reference block for motion compensation prediction referred to by a coding target block of a luminance signal of the current video frame is processed as a target for degradation prediction determination, the processing target block is also processed as a target for degradation prediction determination.

When the encoding control unit 11 determines that the degradation of the luminance signal is not expected to be significant (step S1: No), the chrominance encoding parameter determination unit 116 determines a predetermined encoding parameter (e.g., the number of quantization steps or prediction mode) for the chrominance signal of the block to be encoded that is lower than the reproducibility of the luminance signal, thereby reducing the amount of code (step S2).

In addition, it has been experimentally demonstrated that if the reproducibility of the color difference signal is extremely low when there is almost no degradation of the luminance signal, the subjective quality will be reduced. Therefore, it is desirable to avoid a large difference in the degree of degradation, for example by not making the difference in QP between the luminance signal and the color difference signal too large.

On the other hand, when the encoding control unit 11 determines that the degradation of the luminance signal is expected to be large (step S1: Yes), the chrominance encoding parameter determination unit 116 uses the function to change the predetermined encoding parameters (e.g., the number of quantization steps or the prediction mode) used when it is predicted that the degradation of the luminance signal is not large for the chrominance signal of the block to be encoded, and determines the predetermined encoding parameters (e.g., the number of quantization steps or the prediction mode) that provide a higher degree of reproducibility, thereby increasing the amount of code (step S3).

Specifically, for the color difference signal in the block to be coded, if it is determined that the degradation of the luminance signal is predicted to be large, the coding parameters for reducing the color difference signal by a predetermined amount are determined by changing a predetermined QP (i.e., the number of quantization steps) or quantization matrix coefficient used when the degradation of the luminance signal is predicted to be small, or by selecting a prediction mode (specified by a mode number in H.265 and VVC). Note that coding parameters for coding the color difference signal losslessly or visually losslessly may be determined. When changing the QP (i.e., when changing the quantization matrix coefficient), it is desirable to perform clipping processing, for example, to prevent the QP from changing by 5 or more, since a sudden change in image quality will cause noticeable degradation.

In this way, when a video with a highly complex luminance signal is encoded at a low target bit rate, and significant degradation is expected, the amount of code for the luminance signal must be significantly increased in order to improve image quality. On the other hand, chrominance signals are generally flatter and have less variance than luminance signals, and because the number of pixels is reduced by subsampling, they are less difficult to encode, so a slight increase in the amount of code allocated to the chrominance signal can be expected to improve subjective quality.

The encoding control of this embodiment 1 can improve the subjective quality when compressing and transmitting wide color gamut video.

(Encoding control in the second embodiment)
FIG. 4 is a flowchart showing the encoding control of the encoding control unit 11 according to the second embodiment of the present invention.

First, similarly to step S1 in the first embodiment, the encoding control unit 11 uses the functions of the pre-measurement unit 111, the luminance encoding parameter determination unit 112, the luminance complexity determination unit 114, and the luminance degradation prediction determination unit 115 to determine whether or not significant degradation of the luminance signal is expected in a specific block to be encoded when performing block-based encoding of the video frame to be encoded this time in the moving image (step S11).

When the encoding control unit 11 determines that the degradation of the luminance signal is not expected to be significant (step S11: No), similarly to step S2 in the first embodiment, the chrominance encoding parameter determination unit 116 determines a predetermined encoding parameter (e.g., the number of quantization steps or prediction mode) for the chrominance signal of the block to be encoded that is lower than the reproducibility of the luminance signal, thereby reducing the amount of code (step S12).

On the other hand, when the encoding control unit 11 determines that the luminance signal is expected to be significantly degraded (step S11: Yes), it determines whether the chrominance signal of the block to be encoded is close to achromatic (whether it is within a predetermined range from achromatic) (step S13).

For example, in the case of luminance and color difference signals Y, Cb, and Cr specified in BT.2020, it is possible to determine whether the color difference signals Cb and Cr are both close to the median value (512 in the case of 10 bits).

Then, when the chrominance signal of the block to be coded is within a predetermined range from achromatic (step S13: Yes), the coding control unit 11 determines that the chrominance signal is achromatic, using the function of the chrominance coding parameter determination unit 116, and determines coding parameters to make the chrominance signal completely achromatic, or controls the output control unit 117 to include meta information in the auxiliary information to instruct the output control unit 117 to make the signal achromatic, so that the auxiliary information can be transmitted to the video decoding device 2 (step S14).

In addition, when the color difference signal of the block to be coded is not within a predetermined range from achromatic color (step S13: No), the coding control unit 11 determines whether the color difference signal is within a predetermined high perceptual range (step S15) by using the function of the color difference coding parameter determination unit 116.

For example, by using MacAdam's ellipse, which is a survey of the range of colors perceived as matching on an xy chromaticity diagram, and determining whether the color is within a range where the perception of matching colors is high, it is possible to determine whether the color gamut is narrow or corresponds to a color gamut that is sensitive to color changes such as skin color.

Then, when the color difference signal is within a predetermined high perceptual range (step S15: Yes), the encoding control unit 11 performs the same process as step S3 in the first embodiment by using the function of the color difference encoding parameter determination unit 116. That is, the encoding control unit 11 changes the predetermined encoding parameters (e.g., the number of quantization steps or the prediction mode) used when predicting that the degradation of the luminance signal is not large for the color difference signal of the block to be encoded, determines the predetermined encoding parameters (e.g., the number of quantization steps or the prediction mode) that improve the reproducibility, and increases the amount of code (step S16).

Furthermore, when the chrominance signal is not within a predetermined high perceptual range (step S15: No), the encoding control unit 11 performs the same processing as step S2 in the first embodiment, by using the function of the chrominance encoding parameter determination unit 116. That is, the encoding control unit 11 determines a predetermined encoding parameter (e.g., the number of quantization steps or prediction mode) for the chrominance signal of the block to be encoded that is lower than the reproducibility of the luminance signal, thereby reducing the amount of code (step S12).

The encoding control of this second embodiment can improve the subjective quality when compressing and transmitting wide color gamut video while taking into account the perception of color difference signals.

[Video Decoding Device]
(Overall composition)
5 is a block diagram showing a schematic configuration of a video decoder 2 according to an embodiment of the present invention. The video decoder 2 according to the present embodiment includes a decoding control unit 21 and a video decoding unit 22.

The decoding control unit 21 controls the video decoding unit 22 to perform a decoding process on the video coding signal coded by the video coding device 1 based on the auxiliary information transmitted from the video coding device 1.

The video decoding unit 22 is a processing unit that is controlled by the decoding control unit 21 and performs a decoding process on the video coding signal coded by the video coding device 1 using coding parameters based on the auxiliary information, to generate a decoded video signal. As a typical example, the video decoding unit 22 has an entropy decoding unit 221, an inverse quantization and inverse orthogonal transform unit 222, an addition unit 223, an intra-screen prediction unit 224, a loop filter 225, an inter-screen prediction unit 226, and a switching unit 227.

The entropy decoding unit 221 inputs the video coding signal coded by the video coding device 1 as a bit stream, performs a decoding process on the variable-length code related to the bit stream, which is the inverse process of the entropy coding by the video coding device 1, and outputs the quantized value of the signal of the orthogonal transform coefficient, which is a signal in a predetermined block unit specified by the coding parameters, to the inverse quantization and inverse orthogonal transform unit 222.

The inverse quantization and inverse orthogonal transform unit 222 performs the inverse processing of the quantization unit 124 in the video encoding device 1 on the quantized values of the orthogonal transform coefficient signal obtained from the entropy decoding unit 221 to restore the orthogonal transform coefficient signal, and further performs the inverse processing of the orthogonal transform unit 123 in the video encoding device 1 on this orthogonal transform coefficient signal to restore the difference signal, which is output to the addition unit 223.

The adder 223 adds the difference signal obtained from the inverse quantization and inverse orthogonal transform unit 222 and the prediction signal obtained from the switching unit 227 to generate a decoded block, and outputs the decoded block to the intra-screen prediction unit 224 during intra-coding and decoding, and outputs the decoded block to the inter-screen prediction unit 226 via the loop filter 225 during inter-coding and decoding. The adder 223 also outputs the signal of the generated decoded block to the outside, such as a display or a recording unit (not shown), as a video decoded signal.

During intra-coding decoding, the intra-screen prediction unit 224 temporarily stores the decoded block obtained from the adder unit 223 as an adjacent block of the next block to be decoded, generates a prediction signal of the next block to be decoded based on the adjacent block, and outputs it to the adder unit 223 via the switching unit 227.

The loop filter 225 is a processing unit that applies a so-called deblocking filter, a band pass filter, and SAO that performs offset processing on a block basis to the decoded block obtained from the addition unit 223.

During inter-coding/decoding, the inter-screen prediction unit 226 temporarily stores the decoded blocks obtained from the loop filter 225 on a picture-by-picture basis, generates a prediction signal for the next block to be decoded based on block matching in the reference picture referenced as motion prediction, and outputs the signal to the addition unit 223 via the switching unit 227.

The switching unit 227 is a functional unit that switches between intra-coding and inter-coding and decoding depending on the encoding type.

When the video encoding device 1 transmits a video encoding signal using the encoding control of Example 1 shown in FIG. 3, the decoding control unit 21 controls the video decoding unit 22 to perform a decoding process on the video encoding signal encoded by the video encoding device 1 based on the auxiliary information transmitted from the video encoding device 1, in the same manner as in the existing decoding control.

On the other hand, when the video encoding device 1 transmits a video encoding signal using the encoding control of Example 2 shown in FIG. 4, the auxiliary information may contain meta-information instructing the signal to be achromatized. In this case, the decoding control unit 21 is similar in that it controls the video encoding signal encoded by the video encoding device 1 to be decoded based on the auxiliary information transmitted from the video encoding device 1, but when meta-information is transmitted, it controls the video decoding unit 22 by changing the encoding parameters so as to completely achromatize the color difference signal of the specified block.

The video encoding device 1 and video decoding device 2 according to the present invention configured as described above can improve the subjective quality when compressing and transmitting wide color gamut video, preferably while taking into account the perceptual degree of color difference signals.

For the video encoding device 1 and video decoding device 2 of the above-mentioned embodiment, a program for causing each means of a computer functioning as the video encoding device 1 to function, or a program for causing each means of a computer functioning as the video decoding device 2 to function, can be suitably used. Specifically, a control unit for controlling each means can be configured with a central processing unit (CPU) in a computer, and a storage unit for appropriately storing the programs required to operate each means can be configured with at least one memory. That is, by having such a computer execute the program with the CPU, the functions of each of the above-mentioned means can be realized. Also, each of the above-mentioned means can be configured as part of hardware or software, and can be realized by combining each of them.

The above-mentioned embodiments and examples have been described as representative examples, but it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited by the above-mentioned examples, but is limited only by the scope of the claims.

The present invention can improve the subjective quality when compressing and transmitting wide color gamut video, and is therefore useful for video coding applications for compressing and transmitting wide color gamut video.

REFERENCE SIGNS LIST 1 video encoding device 2 video decoding device 11 encoding control unit 12 video encoding unit 21 decoding control unit 22 video decoding unit 111 advance measurement unit 112 luminance encoding parameter determination unit 113 encoding parameter setting unit 114 luminance complexity determination unit 115 luminance degradation prediction determination unit 116 chrominance encoding parameter determination unit 117 output control unit 118 determination result storage unit 121 preprocessing unit 122 subtraction unit 123 orthogonal transform unit 124 quantization unit 125 inverse quantization and inverse orthogonal transform unit 126 addition unit 127 intra-screen prediction unit 128 loop filter 129 inter-screen prediction unit 130 switching unit 131 entropy encoding unit 132 output unit 221 entropy decoding unit 222 inverse quantization and inverse orthogonal transform unit 223 addition unit 224 Intra-frame prediction unit 225 Loop filter 226 Inter-frame prediction unit 227 Switching unit

Claims (5)

A video encoding device for encoding a video frame including a luminance signal and a color difference signal, comprising:
a video encoding unit that encodes a luminance signal and a color difference signal individually for each of the video frames in units of a predetermined block;
An encoding control unit that variably controls encoding parameters to control the video encoding unit,
a video encoding device characterized in that the encoding control unit has a function of predicting whether deterioration of the luminance signal of a specific block to be encoded will be large, and controlling the video encoding unit to increase the reproducibility of the color difference signal if the deterioration is predicted to be large, and if the deterioration is predicted to be large, further determining whether the color difference signal of the specific block to be encoded of the video frame is within a specified range from achromatic, and if it is determined that the color difference signal is within the specified range from achromatic, treating the color difference signal as achromatic and determining encoding parameters to make it completely achromatic, or controlling the inclusion of meta information instructing the ... 2. The video encoding device according to claim 1, wherein the encoding control unit further has a function of determining whether the color difference signal is within a predetermined range of high perceptual intensity when the color difference signal is not within a predetermined range from achromatic color, and determining encoding parameters for the color difference signal based on the determination result. A video decoding device that receives and decodes a video encoded signal of a video frame encoded by the video encoding device according to claim 2 , comprising:
a video decoding unit that performs a decoding process on the video encoded signal using encoding parameters based on auxiliary information transmitted from the video encoding device;
a decoding control unit that controls the video decoding unit to perform a decoding process on the video encoded signal based on auxiliary information transmitted from the video encoding device,
The video decoding device is characterized in that, when meta information instructing the color difference signal in the block to be decoded to be made achromatic is transmitted as the auxiliary information, the decoding control unit controls the video decoding unit by changing the encoding parameters so as to completely achromatize the color difference signal of the specified block. A program for causing a computer to function as the video encoding device according to claim 1 or 2 . A program for causing a computer to function as the video decoding device according to claim 3 .