JP6941752B1 - Image decoding device, image decoding method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a situation in which the characteristics of a decoded image are changed and affect the subjective image quality. An image decoding device 200 according to the present invention includes a filter unit 250B configured to input a pre-filter processing decoding signal and output a post-filter processing decoding signal, and the filter unit 250B is a reference pixel. Clipping processing is applied to the pre-filtered decoding signal so that the absolute value of the difference between the value and the pixel value of the pre-filtered decoded signal is equal to or less than the predefined threshold value, and the value and filter after clipping processing is applied. It is configured to generate the decoded signal after filtering by the linear weighted sum with the pixel value of the decoded signal before processing, and even if the bit depth changes, the magnitude of the threshold value for the brightness signal and the threshold value for the color difference signal is large or small. Relationships are defined to be preserved. [Selection diagram] Fig. 6

Description

The present invention relates to an image decoding device, an image decoding method and a program.

Conventionally, there is known a technique for realizing a non-linear filter processing by clipping an input signal to "ALF (Adaptive Loop Filter))" with a threshold value (see, for example, Non-Patent Document 1).

Here, the threshold value is defined by a mathematical formula, and the final value is derived according to the set value of the internal bit depth and the like. Such thresholds are defined for the luminance signal and the color difference signal, respectively.

Versatile Video Coding (Draft 5), JVET-N1001

However, in the above-mentioned conventional technique, the magnitude relationship between the threshold value of the luminance signal and the threshold value of the color difference signal is reversed depending on the internal bit depth. As a result, even for the same input signal, there is a problem that the characteristics of the decoded image may change depending on the setting of the internal bit depth, which may affect the subjective image quality.

Therefore, the present invention has been made in view of the above-mentioned problems, and is an image decoding device, an image decoding method, and a program that can prevent a situation in which the characteristics of the decoded image are changed and affect the subjective image quality. The purpose is to provide.

The first feature of the present invention is an image decoding device, which includes a filter unit configured to input a pre-filter processing decoding signal and output a post-filter processing decoding signal, and the filter unit is referred to. Clipping processing is performed on the pre-filter processing decoding signal so that the absolute value of the difference value between the pixel value and the pixel value of the pre-filter processing decoding signal is equal to or less than a predetermined threshold value, and after the clipping processing is performed. Is configured to generate the post-filtered decoding signal by a linear weighted sum of the value of The gist is that it is defined so that the magnitude relationship with the threshold value for the color difference signal is preserved.

A second feature of the present invention is an image decoding method including a step of inputting a pre-filter processing decoding signal and outputting a post-filter processing decoding signal. In the step, a reference pixel value and the pre-filter processing decoding signal are provided. Clipping processing is performed on the pre-filter processing decoding signal so that the absolute value of the difference value from the pixel value of is equal to or less than a predetermined threshold value, and the value after the clipping processing is performed and the pre-filter processing decoding signal. The post-filtered decoded signal is generated by the linear weighted sum with the pixel value of, and even if the internal bit depth changes, the magnitude relationship between the threshold value for the brightness signal and the threshold value for the color difference signal is preserved. The gist is that it is defined in.

A third feature of the present invention is a program used in an image decoding device, in which a computer is made to execute a step of inputting a decoding signal before filtering and outputting a decoding signal after filtering, and in the step, a reference pixel is used. Clipping processing is performed on the pre-filter processing decoding signal so that the absolute value of the difference value between the value and the pixel value of the pre-filter processing decoding signal is equal to or less than a predetermined threshold value, and after the clipping processing is performed. The post-filtered decoded signal is generated by the linear weighted sum of the value and the pixel value of the pre-filtered decoded signal, and even if the internal bit depth changes, the threshold value for the brightness signal and the threshold value for the color difference signal are used. The gist is that the magnitude relation of is defined to be preserved.

According to the present invention, it is possible to provide an image decoding device, an image decoding method, and a program that can prevent a situation in which the characteristics of the decoded image are changed and affect the subjective image quality.

It is a figure which shows an example of the structure of the image processing system 10 which concerns on one Embodiment. It is a figure which shows an example of the functional block of the image coding apparatus 100 which concerns on one Embodiment. It is a figure which shows an example of the functional block of the in-loop filter processing unit 150 of the image coding apparatus 100 which concerns on one Embodiment. It is a figure for demonstrating an example of the function of the filter part 150B of the in-loop filter processing part 150 of the image coding apparatus 100 which concerns on one Embodiment. It is a figure for demonstrating an example of the function of the filter part 150B of the in-loop filter processing part 150 of the image coding apparatus 100 which concerns on one Embodiment. It is a figure for demonstrating an example of the function of the filter part 150B of the in-loop filter processing part 150 of the image coding apparatus 100 which concerns on one Embodiment. It is a figure for demonstrating an example of the function of the filter part 150B of the in-loop filter processing part 150 of the image coding apparatus 100 which concerns on one Embodiment. It is a figure which shows an example of the functional block of the image decoding apparatus 200 which concerns on one Embodiment. It is a figure which shows an example of the functional block of the in-loop filter processing unit 250 of the image decoding apparatus 200 which concerns on one Embodiment. It is a flowchart which shows an example of the processing procedure of the in-loop filter processing unit 250 of the image decoding apparatus 200 which concerns on one Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The components in the following embodiments can be replaced with existing components as appropriate, and various variations including combinations with other existing components are possible. Therefore, the description of the following embodiments does not limit the content of the invention described in the claims.

(First Embodiment)
Hereinafter, the image processing system 10 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 10. FIG. 1 is a diagram showing an image processing system 10 according to an embodiment according to the present embodiment.

As shown in FIG. 1, the image processing system 10 includes an image coding device 100 and an image decoding device 200.

The image coding device 100 is configured to generate encoded data by encoding an input image signal. The image decoding device 200 is configured to generate an output image signal by decoding the coded data.

Here, such coded data may be transmitted from the image coding device 100 to the image decoding device 200 via a transmission line. Further, the coded data may be stored in the storage medium and then provided from the image coding device 100 to the image decoding device 200.

(Image Coding Device 100)
Hereinafter, the image coding apparatus 100 according to the present embodiment will be described with reference to FIG. FIG. 2 is a diagram showing an example of a functional block of the image coding apparatus 100 according to the present embodiment.

As shown in FIG. 2, the image coding apparatus 100 includes an inter-prediction unit 111, an intra-prediction unit 112, a subtractor 121, an adder 122, a conversion / quantization unit 131, and an inverse conversion / dequantization. It has a unit 132, an encoding unit 140, an in-loop filter processing unit 150, and a frame buffer 160.

The inter-prediction unit 111 is configured to generate a prediction signal by inter-prediction (inter-frame prediction).

Specifically, the inter-prediction unit 111 identifies and identifies the reference block included in the reference frame by comparing the frame to be encoded (hereinafter referred to as the target frame) with the reference frame stored in the frame buffer 160. It is configured to determine the motion vector for the referenced block.

Further, the inter-prediction unit 111 is configured to generate a prediction signal included in the prediction block for each prediction block based on the reference block and the motion vector. The inter-prediction unit 111 is configured to output a prediction signal to the subtractor 121 and the adder 122. Here, the reference frame is a frame different from the target frame.

The intra prediction unit 112 is configured to generate a prediction signal by intra prediction (in-frame prediction).

Specifically, the intra prediction unit 112 is configured to specify a reference block included in the target frame and generate a prediction signal for each prediction block based on the specified reference block. Further, the intra prediction unit 112 is configured to output a prediction signal to the subtractor 121 and the adder 122.

Here, the reference block is a block that is referred to for the block to be predicted (hereinafter, the target block). For example, the reference block is a block adjacent to the target block.

The subtractor 121 is configured to subtract the prediction signal from the input image signal and output the prediction residual signal to the conversion / quantization unit 131. Here, the subtractor 121 is configured to generate a prediction residual signal, which is the difference between the prediction signal generated by the intra prediction or the inter prediction and the input image signal.

The adder 122 adds a prediction signal to the prediction residual signal output from the inverse conversion / inverse quantization unit 132 to generate a pre-filter processing decoding signal, and the pre-filter processing decoding signal is combined with the intra prediction unit 112 and the input. It is configured to output to the loop filter processing unit 150.

Here, the pre-filtered decoding signal constitutes a reference block used by the intra prediction unit 112.

The conversion / quantization unit 131 is configured to perform conversion processing of the predicted residual signal and acquire a coefficient level value. Further, the conversion / quantization unit 131 may be configured to quantize the coefficient level value.

Here, the conversion process is a process of converting the predicted residual signal into a frequency component signal. In such a conversion process, a base pattern (transformation matrix) corresponding to the discrete cosine transform (DCT) may be used, or a base pattern (transformation matrix) corresponding to the discrete sine transform (DST). May be used.

The inverse transformation / inverse quantization unit 132 is configured to perform an inverse transformation process of the coefficient level value output from the conversion / quantization unit 131. Here, the inverse transformation / inverse quantization unit 132 may be configured to perform inverse quantization of the coefficient level value prior to the inverse transformation processing.

Here, the inverse conversion process and the inverse quantization are performed in the reverse procedure of the conversion process and the quantization performed by the conversion / quantization unit 131.

The coding unit 140 is configured to encode the coefficient level value output from the conversion / quantization unit 131 and output the coded data.

Here, for example, coding is entropy coding in which codes of different lengths are assigned based on the probability of occurrence of coefficient level values.

Further, the coding unit 140 is configured to encode the control data used in the decoding process in addition to the coefficient level value.

Here, the control data may include size data such as a coding block (CU: Coding Unit) size, a prediction block (PU: Precision Unit) size, and a conversion block (TU: Transfer Unit) size.

The in-loop filter processing unit 150 is configured to perform filter processing on the pre-filter processing decoding signal output from the adder 122 and output the post-filter processing decoding signal to the frame buffer 160.

Further, the in-loop filter processing unit 150 may be configured to use the input image signal and the pre-filter processing decoding signal as inputs to determine parameters related to the filter processing and output the parameters to the coding unit 140. The coding unit 140 may be configured to encode such a parameter and transmit it to the image decoding device 200 as additional information.

Here, for example, the filtering process is an adaptive loop filtering process that reduces the coding distortion of the decoded image.

The frame buffer 160 is configured to store reference frames used by the inter-prediction unit 111.

Here, the filtered decoded signal constitutes a reference frame used by the inter-prediction unit 111.

(In-loop filter processing unit 150)
Hereinafter, the in-loop filter processing unit 150 according to the present embodiment will be described. FIG. 3 is a diagram showing an in-loop filter processing unit 150 according to the present embodiment.

As shown in FIG. 3, the in-loop filter processing unit 150 includes a class determination unit 150A, a filter unit 150B, and a parameter determination unit 150C.

The in-loop filter processing unit 150 can select either application or non-application of the adaptive loop filter processing in units of coded tree blocks (CTU: Coding Tree Unit). When the adaptive loop filter processing is applied, the in-loop filter processing unit 150 can select which filter set to use from the plurality of filter sets.

Each filter set includes a maximum of 25 types (classes) of filters for luminance signals and a class of filters for color difference signals.

As described later, parameters including information related to the application or non-application of the adaptive loop filter processing and information related to the filter set to be used in the adaptive loop filter processing are encoded for each CTU as additional information and image decoding. It is transmitted to the device 200. The parameters are determined by the parameter determination unit 150C, as will be described later.

Here, for example, when the input signal is in the “YCbCr4: 2: 0 format”, the CTU has, for example, a luminance (Y) signal having a size of 128 × 128 pixels and a color difference signal (Cb, Cr) having a size of 64 × 64 pixels. It may be defined as each block divided into sizes.

For the pixels of the luminance signal and the color difference signal belonging to the CTU determined not to apply the adaptive loop filter processing, the determination processing by the class determination unit 150A and the filter processing by the filter unit 150B, which will be described later, can be omitted.

The class determination unit 150A receives the pre-filtering decoding signal as an input, and outputs class determination information indicating which type (class) of filters to use from among a plurality of predetermined types of filters (adaptive loop filters). It is configured as follows.

Here, the class determination unit 150A is configured to divide the pre-filtered decoding signal into small blocks and determine the class to be used for each block. For example, the class determination unit 150A can determine which class of the 25 types of filters should be used for each 4 × 4 pixel block.

Here, as the class determination method, any determination method can be used as long as it is a method that can determine only the information obtained on both the image coding device 100 side and the image decoding device 200 side as input. Can be done.

For example, in Non-Patent Document 1, the above-mentioned class determination is performed using the gradient of the pixel value of the pre-filtered decoding signal. By using only the information obtained on both the image coding device 100 side and the image decoding device 200 side, it is possible to determine the same class on the image decoding device 200 side as on the image decoding device 100 side. It is not necessary to transmit the information from the image coding device 100 side to the image decoding device 200 side.

The filter unit 150B is configured to input the pre-filter processing decoding signal and output the post-filter processing decoding signal.

Specifically, the filter unit 150B receives the pre-filter processing decoding signal, the class determination information output from the class determination unit 150A, and the parameters input from the parameter determination unit 150C (loop filter processing parameter group) as inputs. It is configured to perform filtering and output a decoded signal after filtering.

The value of each pixel of the decoded signal after filtering can be calculated by, for example, the following formula.

Here, I (x, y) is the pixel value of the pre-filtered decoding signal at the coordinates (x, y), and O (x, y) is the filter processing at the coordinates (x, y). The pixel value of the post-decoding signal, (i, j) is the coordinate (reference pixel position) indicating the relative position of the reference pixel with respect to the pixel at the coordinate of (x, y), and C (i, j) is the coordinate (reference pixel position). , The filter coefficient corresponding to the reference pixel position (i, j), K () is the clipping process shown below, and k (i, j) is the threshold used in the clipping process.

K (I, k) = min (k, max (-k, I))
Here, min () is a function that returns the minimum value in the argument, and max () is a function that returns the maximum value in the argument. Therefore, K () is a process of returning -k when the input value I is smaller than -k, returning k when the input value I is larger than k, and returning the input value I as it is otherwise.

That is, in the filter unit 150B, the absolute value of the difference value between the reference pixel value I (x + i, y + j) and the pixel value I (x, y) of the pre-filtered decoding signal is equal to or less than the predetermined threshold value k (i, j). It is configured to perform clipping processing on the decoding signal before filter processing so as to be.

Further, the filter unit 150B is configured to generate a decoded signal after filtering by a linear weighted sum of the value after clipping processing and the pixel value I (x, y) of the decoding signal before filtering. There is.

The filter coefficient C is determined by the parameter determination unit 150C and transmitted to the image decoding apparatus 200 side. In order to reduce the code amount of the information related to the filter coefficient C, the number of filter coefficients C can be reduced by applying the same filter coefficient C to a plurality of pixels. FIG. 4 shows a specific example.

FIG. 4A shows an example of the arrangement of the filter coefficient C in the luminance signal filtering process, and FIG. 4B shows an example of the arrangement of the filter coefficient C in the color difference signal filtering process.

As shown in FIG. 4A, for example, in the luminance signal, 12 types of filter coefficients C0 to C11 are used. In FIG. 4A, the pixel described as X is a pixel position (x, y) whose pixel value is corrected by such a filter process. Pixels to which the same filter coefficient C is applied are arranged point-symmetrically with the pixel position (x, y) as the center.

As shown in FIG. 4B, similarly, with respect to the color difference signal, other filter coefficients are arranged point-symmetrically around the pixel described as X.

For example, when the reference pixel is a pixel outside the picture, the filter processing can be realized by copying the pixel value of the pre-filter processing decoding signal located at the picture boundary (called padding).

Here, FIG. 5 shows an example of filtering processing at the lower end (picture boundary) of the picture.

In FIG. 5A, the grayed out filter coefficients C0 to C3 refer to pixels outside the picture. At this time, as the input to the grayed out filter coefficients C2 and C0, the same pixel value as the pixel value corresponding to the filter coefficient C6 arranged directly above the filter coefficient C2 in FIG. 5A is used.

Similarly, as the input to the grayed out filter coefficient C3, the same pixel value as the pixel value corresponding to the filter coefficient C7 arranged directly above the filter coefficient C3 in FIG. 5A is used and grayed out. As the input to the filter coefficient C1, the same pixel value as the pixel value corresponding to the filter coefficient C5 arranged directly above the filter coefficient C1 in FIG. 5A is used.

Further, in consideration of the point symmetry of the filter coefficient C described above, when a padded value is used for a part of the reference pixel, the padded value is used as an input to the filter coefficient C at the position corresponding to the reference pixel. You can also do it.

In the example of FIG. 5 (b), in addition to the filter processing at the lower end of the picture described in the example of FIG. 5 (a), the padded values of the grayed out filter coefficients C0 to C3 may be input.

For example, as the input to the filter coefficients C0 and C2 in FIG. 5B, the pixel value corresponding to the filter coefficient C6 immediately below the filter coefficient C2 may be padded and used.

Similarly, for the inputs of the filter coefficients C1 and C3, the pixel values corresponding to the filter coefficients C5 and C7 immediately below the filter coefficients C1 and C3 may be padded and used.

In the above example, the filtering process at the lower end of the picture has been described, but the same filtering process can be applied to the upper end and the left and right edges of the picture.

In addition to the picture boundary, if the pixel value beyond the boundary cannot be referred to, such as the boundary of a parallel processing unit of coding called a slice or tile, or the boundary in pipeline processing called a virtual boundary, the above-mentioned The same can be done by applying the filtering method of.

By setting the filter processing at the boundaries such as the picture boundary, the tile boundary, the slice boundary, and the virtual boundary described above as the same processing, the implementation can be simplified as compared with the case where the processing is different for each boundary.

Further, the threshold value used in the clipping process is set for each filter class and each filter coefficient C, respectively.

For example, when there are 25 classes of filters for luminance signals and there are 12 types of filter coefficients C for each class as described above, it is necessary to set a threshold value for a filter coefficient of 25 × 12 = 300 at the maximum. Such a threshold value is determined by the parameter determination unit 150C described later, and is transmitted to the image decoding apparatus 200 side as additional information.

Here, in order to reduce the code amount related to the information related to the threshold value, instead of transmitting the threshold value itself as the information related to the threshold value, which of several predetermined threshold values is used for each filter coefficient. It is also possible to encode only the index information indicating whether to use the threshold value.

When four types of thresholds for the luminance signal and four types of thresholds for the color difference signal are prepared in advance, the thresholds for the luminance signal and the thresholds for the color difference signal are defined as shown in FIG. 6A, for example. Can be done.

Since the variance of the luminance signal tends to be larger than the variance of the color difference signal, as shown in FIG. 6A, the threshold value for the luminance signal is set to be equal to or greater than the threshold value for the color difference signal. Clipping processing that considers the characteristics of each signal becomes possible.

That is, as shown in FIG. 6A, even if the internal bit depth (“bit depth” in FIG. 6) changes, the magnitude relationship between the threshold value for the luminance signal and the threshold value for the color difference signal (for example, for the luminance signal) The threshold value of is greater than or equal to the threshold value for the color difference signal) is defined to be preserved.

Further, as shown in FIG. 6A, the threshold value for the luminance signal and the threshold value for the color difference signal are defined to be calculated by multiplying the values of the same magnification according to the change in the internal bit depth. You may. According to such a configuration, even if the internal bit depth changes, the magnitude relationship between the threshold value for the luminance signal and the threshold value for the color difference signal can be preserved, and the same clipping process can be performed regardless of the internal bit depth.

Here, the internal bit depth means the bit accuracy when calculating the pixel values of the luminance signal and the color difference signal during the coding process and the decoding process. The internal bit depth takes, for example, an integer value of 8 to 16 bits and is transmitted from the image coding device 100 side to the image decoding device 200 side as additional information.

Further, by defining the magnification related to the internal bit depth as a power of 2 as shown in FIG. 6A, such clipping processing can be realized only by bit shifting as shown in FIG. 6B. The processing load on hardware and software can be reduced.

That is, the threshold value for the luminance signal and the threshold value for the color difference signal may be defined so as to be calculated by bit-shifting each of them according to the change in the internal bit depth.

The threshold value corresponding to the index 0 in FIGS. 6 (a) and 6 (b) is the same value as the maximum value that can be expressed by the corresponding internal bit depth. Therefore, by selecting such a threshold value, the filter coefficient C corresponding to such a threshold value is substantially equivalent to not performing clipping processing.

In order to obtain the same effect as the above example, it is not necessary to set the same value for all the threshold values as described above. In the predetermined internal bit depth domain (for example, 8 to 16 bits), the magnitude relation of the threshold value corresponding to each index is not reversed in the luminance signal and the color difference signal, and the luminance signal and the color difference are not reversed. As long as it is guaranteed that the magnitude relation of the threshold values corresponding to the same index is not reversed between the signals and the signals, there is no problem even if the magnifications for the respective threshold values are different values.

When the threshold value for the luminance signal of N types (N is a natural number of 1 or more) and the threshold value for the color difference signal to which the indexes of 0 to N-1 are assigned are provided, the luminances having the same index are provided. The threshold value for the signal and the threshold value for the color difference signal may be defined to be calculated by multiplying by the same magnification according to the internal bit depth.

Further, in the above example, the case where the threshold value is multiplied by the magnification according to the internal bit depth has been described, but the process may be a process of adding an offset value instead of the magnification.

Even when the internal bit depth of the luminance signal and the internal bit depth of the color difference signal are different, the luminance signal can be defined by defining the threshold for the luminance signal and the threshold for the luminance signal as shown in FIG. And when the dynamic range of the color difference signal is converted to be the same, it can be defined so that the magnitude relationship of the threshold value used in the clipping process between the luminance signal and the color difference signal does not always change.

Further, in the above example, the case where the threshold value is set for each class and each filter coefficient C has been described. For example, the same threshold value is set for all the filter coefficients C for each class, that is, the threshold value is set to 1 for each class. It is also possible to set them one by one. In this case, since the number of threshold values to be transmitted is reduced, the amount of code related to the index of the threshold value can be reduced.

Further, as will be described later, a flag indicating whether or not clipping processing is performed for each class is transmitted prior to the index of the threshold value. Therefore, when there is only one type of threshold value for each class, the index 0 described above is supported. It is not necessary to define the threshold value (equivalent to no clipping process). Therefore, in the above example, since the patterns that can take the threshold value can be reduced from 4 types to 3 types, further reduction of the code amount related to the index of the threshold value can be expected.

In the above example, the case where different values are set for the threshold value for the luminance signal and the threshold value for the color difference signal has been described, but both can be set to the same value. Thereby, for example, the circuit related to the clipping process of the luminance signal and the color difference signal can be standardized in the hardware, and the circuit scale can be reduced.

Further, even if the threshold value for the luminance signal and the threshold value for the color difference signal are defined to be calculated by performing an operation according to the current internal bit depth based on the case where the internal bit depth is 10 bits. good.

For example, in FIG. 6A, there are four types of threshold values at 10 bits of the brightness signal of 1024, 181, 32, and 6, and four types of threshold values of the color difference signal at 10 bits of 1024, 161, 25, and 4. An example is shown in which the final threshold value is obtained by multiplying a power of 2 according to the value of the current internal bit depth (bitdepth in FIG. 6) based on the case where.

Here, in FIG. 6, the threshold value at 10 bits is represented by a specific numerical value (1024, 181 ..., etc.), but this may be defined in the form of a mathematical formula.

For example, as shown in FIG. 7, the threshold value at 10 bits of the luminance signal is set to "2 ^ (10 (10 × (4-index) / 4) (here, index = 0,1,2,3)). , It may be defined to obtain the final threshold value according to the current internal bit depth by multiplying it by "2 ^ (bitdepth-10)".

Similarly, in the definition of the color difference signal shown in FIG. 7, “2 ^ (8 × (3-index) / 4) × 2 ^ (2)” is the threshold value at the time of 10 bits, and “2 ^ (bitdepth-10)” is defined. ) ”, It can be considered that the threshold value according to the current internal bit depth is calculated.

The parameter determination unit 150C receives the input image signal and the pre-filtered decoding signal as inputs, determines the parameters related to the adaptive loop filter and outputs them as additional information to the coding unit 140, and outputs the determined parameters to the filter unit 150B. It is configured as follows.

The parameters determined by the parameter determination unit 150C include, for example, the following.

First, such a parameter includes a filter set on a frame-by-frame basis. Here, one filter set includes a filter for a maximum of 25 classes of luminance signals and a filter for one class of color difference signals. For each class of filters, the value of the filter coefficient, the flag indicating whether or not clipping processing is performed, the index of the threshold value used in the clipping processing in each filter coefficient when clipping processing is performed in such a class, and the like are determined.

The parameter determination unit 150C has a plurality of filter sets for a certain frame, and can select which filter set to use for each region as described later.

Second, such parameters include, for example, a flag indicating whether or not to apply the adaptive loop filter for each CTU. When the adaptive loop filter is applied, the parameter determination unit 150C can set index information indicating which of the plurality of filter sets is used.

As a method for determining such parameters, a known method can be used, and thus details will be omitted.

Further, although not shown in FIG. 3, the parameter determination unit 150C may use the determination result by the class determination unit 150A or the result of the filter unit 150B performed by tentative parameter setting for the parameter determination.

(Image Decoding Device 200)
Hereinafter, the image decoding apparatus 200 according to the present embodiment will be described with reference to FIG. 7. FIG. 7 is a diagram showing an example of a functional block of the image decoding apparatus 200 according to the present embodiment.

As shown in FIG. 7, the image decoding device 200 includes a decoding unit 210, an inverse transformation / inverse quantization unit 220, an adder 230, an inter-prediction unit 241 and an intra-prediction unit 242, and an in-loop filter processing unit. It has 250 and a frame buffer 260.

The decoding unit 210 is configured to decode the coded data generated by the image coding device 100 and decode the coefficient level value.

Here, for example, the decoding is the entropy decoding in the reverse procedure of the entropy coding performed by the coding unit 140.

Further, the decoding unit 210 may be configured to acquire control data by decoding the coded data.

As described above, the control data may include size data such as a coded block size, a predicted block size, and a conversion block size.

The inverse transformation / inverse quantization unit 220 is configured to perform an inverse transformation process of the coefficient level value output from the decoding unit 210. Here, the inverse transformation / inverse quantization unit 220 may be configured to perform inverse quantization of the coefficient level value prior to the inverse transformation processing.

Here, the inverse conversion process and the inverse quantization are performed in the reverse procedure of the conversion process and the quantization performed by the conversion / quantization unit 131.

The adder 230 adds a prediction signal to the prediction residual signal output from the inverse conversion / inverse quantization unit 220 to generate a pre-filter processing decoding signal, and uses the pre-filter processing decoding signal as an intra prediction unit 242 and an in-loop. It is configured to output to the filter processing unit 250.

Here, the pre-filtered decoding signal constitutes a reference block used by the intra prediction unit 242.

Like the inter-prediction unit 111, the inter-prediction unit 241 is configured to generate a prediction signal by inter-prediction (inter-frame prediction).

Specifically, the inter-prediction unit 241 is configured to generate a prediction signal for each prediction block based on the motion vector decoded from the coded data and the reference signal included in the reference frame. The inter-prediction unit 241 is configured to output a prediction signal to the adder 230.

Like the intra prediction unit 112, the intra prediction unit 242 is configured to generate a prediction signal by intra prediction (in-frame prediction).

Specifically, the intra prediction unit 242 is configured to specify a reference block included in the target frame and generate a prediction signal for each prediction block based on the specified reference block. The intra prediction unit 242 is configured to output a prediction signal to the adder 230.

Similar to the in-loop filter processing unit 150, the in-loop filter processing unit 250 performs filter processing on the pre-filter processing decoding signal output from the adder 230, and outputs the post-filter processing decoding signal to the frame buffer 260. It is configured to do.

Here, for example, the filtering process is an adaptive loop filtering process that reduces the coding distortion of the decoded image.

Like the frame buffer 160, the frame buffer 260 is configured to store reference frames used by the inter-prediction unit 241.

Here, the filtered decoded signal constitutes a reference frame used by the inter-prediction unit 241.

(In-loop filter processing unit 250)
Hereinafter, the in-loop filter processing unit 250 according to the present embodiment will be described. FIG. 9 is a diagram showing an in-loop filter processing unit 250 according to the present embodiment.

As shown in FIG. 9, the in-loop filter processing unit 250 includes a class determination unit 250A and a filter unit 250B.

Similar to the class determination unit 150A, the class determination unit 250A receives the pre-filter processing decoding signal as an input, and outputs class determination information as to which class of filters to use from among a plurality of predetermined in-loop filters. It is configured to do.

Similar to the filter unit 150B, the filter unit 250B is based on the pre-filtering decoding signal, the class determination information determined by the class determination unit 250A, and the parameters transmitted as additional information from the image coding device 100 side. It is configured to perform filtering and output a decoded signal after filtering.

FIG. 10 is a flowchart showing an example of a processing procedure of the in-loop filter processing unit 250 of the image decoding apparatus 200 according to the present embodiment.

As shown in FIG. 10, in step S101, the in-loop filter processing unit 250 receives the pre-filter processing decoding signal as an input, and determines which class of filter is used from among a plurality of predetermined in-loop filters. Output class judgment information.

In step S102, the in-loop filter processing unit 250 is based on the pre-filter processing decoding signal, the class determination information determined by the class determination unit 250A, and the parameters transmitted as additional information from the image coding apparatus 100 side. Filter processing is executed, and the decoding signal is output after the filtering processing.

According to the image coding device 100 and the image decoding device 200 according to the present embodiment, the dynamic ranges of the luminance signal and the color difference signal are the same for the threshold processing of the input signal of the adaptive insertion filter regardless of the setting of the internal bit depth. Since the magnitude relationship between the threshold value for the luminance signal and the threshold value for the color difference signal does not change when converted to, it is possible to prevent the characteristics of the subjective image quality from being unintentionally changed.

The image coding device 100 and the image decoding device 200 described above may be implemented as programs that cause a computer to execute each function (each step).

In the above-described embodiment, the present invention has been described by taking application to the image coding device 100 and the image decoding device 200 as an example, but the present invention is not limited to such an example, and the image coding device is not limited to this. The same applies to an image coding / decoding system having each function of the 100 and the image decoding device 200.

10 ... Image processing system 100 ... Image coding device 111, 241 ... Inter prediction unit 112, 242 ... Intra prediction unit 121 ... Subtractor 122, 230 ... Adder 131 ... Conversion / quantization unit 132, 220 ... Reverse conversion / reverse Quantization unit 140 ... Coding unit 150, 250 ... In-loop filter processing unit 150A, 250A ... Class determination unit 150B, 250B ... Filter unit 150C ... Parameter determination unit 160, 260 ... Frame buffer 200 ... Image decoding device 210 ... Decoding unit

Claims (7)

It is an image decoding device
A class determination unit configured to determine which class of filter to use by using the pre-filtered decoding signal as an input.
A parameter determination unit configured to determine the filter coefficient for each class,
A filter unit configured to input the pre-filtered decoded signal and output the post-filtered decoded signal is provided.
In the filter unit, the reference pixel value and the pixel value of the pre-filtered decoded signal are such that the absolute value of the difference between the reference pixel value and the pixel value of the pre-filtered decoded signal is equal to or less than a predetermined threshold value. Clipping processing is performed on the difference value between Is composed of
The threshold is set for each class and each filter coefficient.
An image decoding apparatus, which is defined so that the magnitude relationship between the threshold value for a luminance signal and the threshold value for a color difference signal is preserved even if the internal bit depth changes. The first aspect of the present invention is that the threshold value for the luminance signal and the threshold value for the color difference signal are defined so as to be calculated by multiplying them by the same magnification according to the change in the internal bit depth. The image decoding device described. The image decoding apparatus according to claim 2, wherein the magnification is defined as a power of 2. N types of thresholds (N is a natural number of 1 or more) to which an index of 0 to N-1 is assigned and a threshold value for the color difference signal are provided.
A claim characterized in that the threshold value for the luminance signal and the threshold value for the color difference signal having the same index are defined to be calculated by multiplying by the same magnification according to the internal bit depth. Item 2. The image decoding apparatus according to item 2 or 3. The image decoding apparatus according to any one of claims 2 to 4, wherein the threshold value for the luminance signal and the threshold value for the color difference signal are defined to have the same value. It is an image decoding method
Step A of determining which class of filter to use with the pre-filtered decoding signal as input, and
Step B of determining the filter coefficient for each class and
It has a step C in which the pre-filter processing decoding signal is input and the post-filter processing decoding signal is output.
In the step C, the reference pixel value and the pixel value of the pre-filtered decoded signal are such that the absolute value of the difference between the reference pixel value and the pixel value of the pre-filtered decoded signal is equal to or less than a predetermined threshold value. Clipping processing is performed on the difference value between the two, and the post-filter processing decoding signal is generated by the linear weighted sum of the value after the clipping processing, the filter coefficient, and the pixel value of the pre-filter processing decoding signal.
The threshold is set for each class and each filter coefficient.
An image decoding method, characterized in that the magnitude relationship between the threshold value for a luminance signal and the threshold value for a color difference signal is defined to be preserved even if the internal bit depth changes. A program that causes a computer to function as an image decoding device.
A class determination unit configured to determine which class of filter to use by using the pre-filtered decoding signal as an input.
A parameter determination unit configured to determine the filter coefficient for each class,
A filter unit configured to input the pre-filtered decoded signal and output the post-filtered decoded signal is provided.
In the filter unit, the reference pixel value and the pixel value of the pre-filtered decoded signal are such that the absolute value of the difference between the reference pixel value and the pixel value of the pre-filtered decoded signal is equal to or less than a predetermined threshold value. Clipping processing is performed on the difference value between Is composed of
The threshold is set for each class and each filter coefficient.
A program characterized in that the magnitude relationship between the threshold value for a luminance signal and the threshold value for a color difference signal is preserved even if the internal bit depth changes.

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