Encoding device, decoding device, program, and method

Abstract

To reduce a block distortion even in a case of a high-luminance portion of an SDR signal, and an HDR signal without deteriorating compression effect.SOLUTION: An encoding device 1 includes: a transformation unit 13 configured to calculate an orthogonal transform coefficient by performing an orthogonal transformation process on a residual image indicating a difference between an input image and a predicted image of the input image; a quantization unit 14 configured to generate a quantization coefficient by quantizing the orthogonal transform coefficient on the basis of a quantization parameter; an entropy encoding unit 24 configured to generate encoded data by encoding the quantization coefficient; an image decoding unit 10 configured to restore an orthogonal transform coefficient from the quantization coefficient on the basis of the quantization parameter and generate a reconstructed image by adding the predicted image to a residual image restored by performing inverse orthogonal transformation on the orthogonal transform coefficient; and a deblocking filtering unit 18 configured to perform a filtering process on the reconstructed image. The deblocking filtering unit 18 controls a filtering strength depending on a luminance signal level of the reconstructed image and the quantization parameter.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an encoding device, a decoding device, and a program for performing deblocking filter processing. [Background technology]

[0002] In mainstream video coding methods, such as MPEG, video units called frames (or pictures) are divided into small block-shaped regions to facilitate real-time processing, and coding (compression) is performed on a block-by-block basis using techniques such as transformation and prediction. In such coding methods, differences in coding control between adjacent blocks cause quality differences at block boundaries that are perceived as distortion. Recent coding methods such as H.264 / AVC and H.265 / HEVC use a process called a deblocking filter to reduce such coding distortion.

[0003] Block distortion is caused by signal degradation at the boundary between adjacent blocks due to quantization of orthogonal transform coefficients, resulting in abrupt signal fluctuations in adjacent regions that should be smooth. Deblocking filters for reducing this distortion are generally designed as low-pass filters that smooth signal fluctuations. Since the amount of signal degradation varies depending on the coarseness of quantization, the strength of the filter is controlled by a quantization parameter that specifies the coarseness of quantization (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Recommendation ITU-T H.265,(04 / 2013)“,High efficiency video coding”,International Telecommunication Union,April 2013 Summary of the Invention

[0005] An encoding device according to one embodiment is an encoding device for encoding an input image, comprising: a transform unit for performing an orthogonal transform process on a residual image indicating a difference between an input image and a predicted image of the input image to calculate an orthogonal transform coefficient, a quantization unit for quantizing the orthogonal transform coefficient based on a quantization parameter to generate a quantized coefficient, an entropy encoding unit for encoding the quantized coefficient to generate encoded data, an image decoding unit for restoring an orthogonal transform coefficient from the quantization coefficient based on the quantization parameter, performing an inverse orthogonal transform on the orthogonal transform coefficient, and adding the predicted image to the restored residual image to generate a reconstructed image, and a deblocking filter unit for performing a filter process on the reconstructed image. The deblocking filter unit controls a filter strength according to a luminance signal level of the reconstructed image and the quantization parameter.

[0006] A decoding device according to one embodiment is a decoding device for decoding coded data of an input image, and includes an entropy decoding unit that decodes the coded data and obtains quantized coefficients obtained by quantizing orthogonal transform coefficients, an image decoding unit that reconstructs orthogonal transform coefficients from the quantized coefficients based on a quantization parameter, performs inverse orthogonal transform on the orthogonal transform coefficients, and adds a predicted image to the reconstructed residual image to generate a reconstructed image, and a deblocking filter unit that performs a filtering process on the reconstructed image. The deblocking filter unit controls a filter strength according to a luminance signal level of the reconstructed image and the quantization parameter. [Brief description of the drawings]

[0007] [Figure 1] FIG. 4 is a diagram showing the correspondence relationship between signal levels and luminance levels. [Diagram 2] 1 is a block diagram showing an example of the configuration of an encoding device according to an embodiment of the present invention; [Diagram 3] FIG. 13 is a diagram illustrating block boundaries on which deblocking filter processing is performed. [Figure 4]1 is a block diagram showing an example of the configuration of a decoding device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] As a feature of new video media, HDR (high dynamic range) signals have been standardized, which expand the range of black and white that cannot be expressed with conventional video signals. Compared to conventional SDR (standard dynamic range) signals, HDR signals record a wide range of light intensity (i.e., from dark to bright) within a limited bit depth, so a more extreme signal suppression process called gamma correction is added. HDR methods currently include the HLG (Hybrid-Log Gamma) method specified in ARIB STD-B67 and the PQ (Perceptual Quantize) method specified in SMPTE ST.2084, and these methods have been internationally standardized by ITU-R as Recommendation ITU-R BT.2100. It is possible that other methods will be specified in the future.

[0009] Figure 1 shows the relationship (inverse gamma correction) between the luminance signal level of an image and the display luminance level displayed on a display device for an SDR signal and HDR signals of the HLG and PQ formats. Note that since the HLG format is a relative system in which the peak luminance of the display device is the maximum value, the peak luminance in the figure is set to 1000 cd / m 2 Similarly, since conventional SDR signals are also relative systems with the peak luminance of the display device as the maximum value, a currently available commercially available display with a peak luminance of 250 cd / m 2 Shown as:

[0010] In HDR signals, the change in display luminance level (brightness) in response to fluctuations in the luminance signal level is greater than in conventional SDR signals. Therefore, in areas with high signal levels, block noise caused by quantization distortion is exaggerated compared to conventional signal degradation. In particular, in the PQ method, which has the greatest degree of signal suppression, the fluctuation in display luminance level in response to luminance signal level is significant, and the effect of signal degradation due to block distortion is also significant. To reduce this phenomenon, it is common to take measures to reduce the quantization parameter according to the signal level.

[0011] In conventional deblocking filters, the threshold for switching the filter strength to achieve interblock smoothing is predetermined for each frame according to the quantization parameter, and control according to the luminance signal level is not performed. Therefore, in HDR signals, the difference between the luminance signal level and the display luminance level has a strong nonlinearity, making it difficult for conventional deblocking filters to sufficiently reduce block distortion. In addition, conventional SDR signals also have nonlinearity due to gamma correction, so there was an issue that the effect of the deblocking filter was reduced in areas with high luminance levels.

[0012] In addition, although it is possible to reduce the average error amount of a block by making the quantization parameter smaller than necessary, the effect of the deblocking filter is also reduced by making the quantization parameter smaller, and it is not possible to sufficiently improve the noticeable difference in luminance signal level at the boundary. In addition, there is a problem that the amount of information increases when the quantization parameter is made smaller, which reduces the compression effect.

[0013] In view of the above circumstances, the present disclosure aims to provide an encoding device, a decoding device, and a program capable of reducing block distortion in high-brightness areas of SDR signals and HDR signals without compromising the compression effect.

[0014] An encoding device according to one embodiment is an encoding device for encoding an input image, and includes: a transform unit that performs an orthogonal transform process on a residual image indicating a difference between an input image and a predicted image of the input image to calculate an orthogonal transform coefficient, a quantization unit that quantizes the orthogonal transform coefficient based on a quantization parameter to generate a quantized coefficient, an entropy encoding unit that encodes the quantized coefficient to generate encoded data, an image decoding unit that restores an orthogonal transform coefficient from the quantization coefficient based on the quantization parameter, performs an inverse orthogonal transform on the orthogonal transform coefficient, and adds the predicted image to the restored residual image to generate a reconstructed image, and a deblocking filter unit that performs a filter process on the reconstructed image. The deblocking filter unit controls a filter strength according to a luminance signal level of the reconstructed image and the quantization parameter.

[0015] A decoding device according to one embodiment is a decoding device for decoding coded data of an input image, and includes an entropy decoding unit that decodes the coded data and obtains quantized coefficients obtained by quantizing orthogonal transform coefficients, an image decoding unit that reconstructs orthogonal transform coefficients from the quantized coefficients based on a quantization parameter, performs inverse orthogonal transform on the orthogonal transform coefficients, and adds a predicted image to the reconstructed residual image to generate a reconstructed image, and a deblocking filter unit that performs a filtering process on the reconstructed image. The deblocking filter unit controls a filter strength according to a luminance signal level of the reconstructed image and the quantization parameter.

[0016] According to such an encoding device and a decoding device, it is possible to change the filter strength according to the luminance signal level, and to reduce block distortion not only for SDR signals but also for HDR signals without compromising the compression effect.

[0017] Hereinafter, one embodiment will be described in detail with reference to the drawings.

[0018] (encoding device) An encoding device according to an embodiment will be described below. Fig. 2 shows an example of the configuration of an encoding device according to an embodiment. The encoding device 1 shown in Fig. 2 includes a block division unit 11, a subtraction unit 12, a transformation unit 13, a quantization unit 14, an inverse quantization unit 15, an inverse transformation unit 16, an addition unit 17, a deblocking filter unit 18, a sample adaptive offset unit 19, a storage unit 20, an intra prediction unit 21, a motion compensation prediction unit 22, a switching unit 23, and an entropy encoding unit 24. Note that instead of or in addition to the sample adaptive offset unit 19, a processing unit that performs other post-filter processing may be provided.

[0019] The block division unit 11 divides an input image, that is, a frame to be coded, into a plurality of blocks, and outputs the block images to the subtraction unit 12. The size of the blocks may be variable, and may be, for example, 32×32 pixels, 16×16 pixels, 8×8 pixels, or 4×4 pixels.

[0020] The subtraction unit 12 subtracts each pixel value of the predicted image of the input image from each pixel value of the block image input from the block division unit 11 to generate a residual image indicating the difference between the block image and the predicted image, and outputs the residual image to the conversion unit 13. The predicted image is input via a switching unit 23 from an intra prediction unit 21 or a motion compensation prediction unit 22, which will be described later.

[0021] The transform unit 13 performs an orthogonal transform process on the residual image input from the subtraction unit 12 to calculate orthogonal transform coefficients, and outputs the orthogonal transform coefficients for each block to the quantization unit 14.

[0022] The quantization unit 14 quantizes the orthogonal transform coefficients for each block input from the transformation unit 13 based on a quantization parameter (qP) that specifies the coarseness of quantization to generate quantization coefficients, and outputs the quantization coefficients to the inverse quantization unit 15 and the entropy coding unit 24. More specifically, the quantization unit 14 generates the quantization coefficients by dividing the orthogonal transform coefficients for each block input from the transformation unit 13 by a quantization step derived from the quantization parameter. For example, the value of the quantization parameter ranges from 0 to 51, and the quantization parameter is associated such that an increase of 6 in the quantization parameter doubles the quantization step (i.e., the quantization parameter and the logarithm of the quantization step are proportional).

[0023] The inverse quantization unit 15 reconstructs the orthogonal transform coefficients from the quantization coefficients input from the quantization unit 14 based on the quantization parameter, and outputs the reconstructed orthogonal transform coefficients to the inverse transform unit 16. More specifically, the inverse quantization unit 15 reconstructs the orthogonal transform coefficients for each block by multiplying the quantization coefficients input from the quantization unit 14 by a quantization step derived from the quantization parameter.

[0024] The inverse transform unit 16 performs inverse orthogonal transform on the orthogonal transform coefficients input from the inverse quantization unit 15 to generate a residual image, and outputs the generated residual image to the addition unit 17. For example, when the transform unit 13 performs a discrete cosine transform, the inverse transform unit 16 performs an inverse discrete cosine transform.

[0025] The adder 17 adds each pixel value of the residual image input from the inverse transformer 16 and the predicted image input from the switching unit 23 to generate a reconstructed image, and outputs the reconstructed image to the deblocking filter unit 18.

[0026] The deblocking filter unit 18 performs a filter process on the reconstructed image input from the adder unit 17, and outputs the reconstructed image after the filter process to the sample adaptive offset unit 19. The deblocking filter unit 18 controls the filter strength according to the luminance signal level (pixel value of the luminance component) of the reconstructed image and the quantization parameter. Details of this process will be described later.

[0027] The sample adaptive offset unit 19 classifies the image input from the deblocking filter unit 18 on a pixel-by-pixel basis, adds an offset according to the classification to each pixel value, and outputs the result as a decoded image to the storage unit 20. The sample adaptive offset unit 19 also outputs sample adaptive offset information to the entropy coding unit 24.

[0028] The intra prediction unit 21 refers to the decoded image stored in the storage unit 20, performs intra prediction to generate an intra prediction image, and outputs the intra prediction image to the switching unit 23. In addition, the intra prediction unit 21 outputs the selected intra prediction mode to the entropy coding unit 24.

[0029] The motion compensation prediction unit 22 generates a motion vector by a technique such as block matching with reference to the decoded image stored in the storage unit 20, and outputs information on the motion vector to the entropy coding unit 24. Furthermore, the motion compensation prediction unit 22 generates a motion compensation predicted image based on the motion vector, and outputs the motion compensation predicted image to the switching unit 23.

[0030] The switching unit 23 switches between the intra-predicted image input from the intra-prediction unit 21 and the motion-compensated predicted image input from the motion-compensated prediction unit 22, and outputs the predicted image of the decoded image (intra-predicted image or motion-compensated predicted image) to the subtraction unit 12 and the addition unit 17.

[0031] The image decoding unit 10 is configured with the inverse quantization unit 15, the inverse transform unit 16, the addition unit 17, the intra prediction unit 21, the motion compensation prediction unit 22, and the switching unit 23. As described above, the image decoding unit 10 reconstructs orthogonal transform coefficients from the quantization coefficients based on the quantization parameter, and generates a reconstructed image by performing an inverse orthogonal transform on the orthogonal transform coefficients and adding a predicted image to the reconstructed residual image.

[0032] The entropy coding unit 24 performs entropy coding on the quantization coefficients input from the quantization unit 14, the intra prediction mode input from the intra prediction unit 21, the predicted motion vector information input from the motion compensation prediction unit 22, the filter information input from the deblocking filter unit 18, and the sample adaptive offset information input from the sample adaptive offset unit 19, compresses the data, generates coded data, and outputs the coded data to the outside of the coding device 1. For the entropy coding, any entropy coding method such as zeroth order exponential Golomb code or CABAC (Context-based Adaptive Binary Arithmetic Coding) can be used.

[0033] (Deblocking filter section) Next, the details of the deblocking filter unit 18 will be described. In this embodiment, the block size on which the deblocking filter unit 18 performs processing is, for example, 8×8 pixels. The deblocking filter unit 18 first obtains a boundary strength Bs (Boundary Strength) value indicating the strength of the smoothing process for each block. The Bs value is set to 0, 1, or 2.

[0034] Figure 3 shows block boundaries on which deblocking filter processing is performed. An example of deblocking filter processing compliant with the H.265 / HEVC standard will be described with reference to Figure 3. If block P or Q is a block that performs intra prediction, the Bs value is set to 2. If blocks P and Q are blocks that perform inter prediction and at least one of the following conditions is satisfied, the Bs value is set to 1, and otherwise the Bs value is set to 0. Block P or Q contains significant (non-zero) orthogonal transform coefficients and is the boundary of a transform unit TU (Transform Unit). The number of motion vectors or the reference pictures of blocks P and Q are different. The absolute value of the difference between the motion vectors of blocks P and Q is 4 pixels or more.

[0035] The deblocking filter unit 18 does not perform filtering when the Bs value is 0. Below, a description will be given taking the vertical block boundary shown in Fig. 3 as an example. When the Bs value is 1 or 2, filtering is performed only when the following formula (1) is satisfied.

[0036]

number

[0037] Furthermore, when performing the filtering process, the deblocking filter unit 18 applies a strong filter when all of the following conditional expressions (2) to (7) are satisfied, and applies a weak filter in other cases.

[0038]

number

[0039] Thresholds β and t C The value of is the average value Q of the quantization parameters of adjacent blocks P and Q. av The deblocking filter unit 18 changes depending on Q av and thresholds β and t C An example of the reference table is shown in Table 1. C are the thresholds β',t C ' is written as '. av ,β',t C ' may be a value to which an offset is added in frame or slice units.

[0040] [Table 1]

[0041] If the bit depth is B, the thresholds β and t C are expressed by equations (8) and (9), respectively, where <<1 means a 1-bit arithmetic left shift operation.

[0042]

number

[0043] In the present invention, the deblocking filter unit 18 shifts the reference table according to the newly added luminance signal level (pixel value of the luminance component) L, and adjusts the thresholds β and t C The value of the luminance signal level L is set to, for example, (p00+p03+q00+q03) / 4 or (p00+p01+p02+p03+q00+q01+q02+q03) / 8. Note that the method of determining the luminance signal level L is just an example, and is not limited to this.

[0044] The deblocking filter unit 18 acquires a format that specifies the dynamic range of the luminance values ​​of the input image. The video format is transmitted by a high-level syntax called Sequence parameter set in the H.265 / HEVC format, for example, and it is generally possible for the decoding device to identify the type of signal. In this embodiment, the format is, for example, three types: SDR, HLG, and PQ. The deblocking filter unit 18 controls the filter strength according to the luminance signal level L, taking into consideration that the difference in luminance signal level has a much greater effect on the display luminance in HDR formats such as the PQ format and the HLG format compared to the SDR format. Specifically, the deblocking filter unit 18 controls the filter strength according to the luminance signal level L, taking into consideration the effect of the difference in β' and t C ', Q av β'[Q av ] and t C '[Q av ], and the threshold value β'[Q av -a] and t C '[Q av-b] is controlled by the shift amounts a and b. The shift amounts a and b are determined, for example, according to the criterion of equation (10). Equation (10) shows an example of the shift amounts a and b when the luminance signal level L is normalized to 0 to 1.0. The deblocking filter unit 18 may determine the shift amounts a and b according to the requirements of each application, or may simply set a=b. Moreover, when a=0 or b=0, the thresholds β',t C Alternatively, only one of the bits ' may be shifted. For SDR signals if (L < 0.75) a=0; else if (L >= 0.75) a=2; if (L < 0.75) b=0; else if (L >= 0.75) b=1; For HLG signals if (L < 0.5) a=0; else if (L >= 0.5 && L < 0.75) a=2; else if (L >= 0.75) a=5; if (L < 0.5) b=0; else if (L >= 0.5 && L < 0.7) b=3; else if (L >= 0.7) b=6; For PQ signals if (L < 0.3) a=-1; else if (L >= 0.3 && L < 0.4) a=0; else if (L >= 0.4 && L < 0.5) a=1; else if (L >= 0.5 && L < 0.7) a=5; else if (L >= 0.7 && L < 0.85) a=10; else if (L >= 0.85 && L < 0.95) a=12; else if (L >= 0.95) a=15; if (L < 0.3) b=-1; else if (L >= 0.3 && L < 0.5) b=0; else if (L >= 0.5 && L < 0.7) b=1; else if (L >= 0.7 && L < 0.95) b=5; else if (L >= 0.95) b=7; (10)

[0045] For example, when the shift amount a=b=5, the deblocking filter unit 18 uses the thresholds β′ and t C ' is shifted to the left by 5. The results are shown in Table 2. Note that if the shift amount a is negative, it is shifted to the right. Note that, as shown in the table, the thresholds β' and t C When β' becomes 0, the lower limit of the subsequent thresholds is also set to 0. C When ' reaches the upper limit of 64 or 24, it is complemented with the upper limit value.

[0046] [Table 2]

[0047] The deblocking filter unit 18 adjusts the thresholds β′ and t C By shifting ', Q av It is possible to adaptively control the threshold value for switching the filter strength according to the threshold values ​​β' and t C' to the right, the thresholds β and t C Since the value of increases, it becomes easier to satisfy the above conditional expressions (2) to (7), and it becomes easier to apply a strong filter. Therefore, in the encoding device 1 according to the present invention, when the luminance signal level L is high, it becomes easier to apply a strong filter in the deblocking filter unit 18, and as a result, it is possible to reduce the occurrence of block distortion without impairing the compression effect.

[0048] In this manner, in the encoding device 1, the deblocking filter unit 18 controls the filter strength in accordance with the luminance signal level of the reconstructed image and the quantization parameter. In one embodiment, the deblocking filter unit 18 controls the filter strength in accordance with the first value (Q av ) and the second value (β, t C ) and holds filter strength setting information (reference table) indicating a correspondence relationship between the quantization parameters of the first and second blocks. The deblocking filter unit 18 modifies the filter strength setting information according to the luminance signal level of the reconstructed image, and derives a second value by applying the first value to the modified filter strength setting information. The first value is a value determined by the average value of the quantization parameters of two adjacent blocks in the reconstructed image. The second value is a value that functions as a threshold for switching the filter strength. The deblocking filter unit 18 switches the filter strength using the second value.

[0049] In one embodiment, the deblocking filter unit 18 controls the filter strength according to a format that defines the dynamic range of the luminance values ​​of the input image. The deblocking filter unit 18 controls the filter strength according to a first value (Q av ) and the second value (β, t C), and modification information (see formula (10)) that defines a method of modifying the filter strength setting information for each format. The deblocking filter unit 18 identifies a modification method corresponding to the format applied to the input image based on the modification information, modifies the filter strength setting information according to the specified modification method in accordance with the luminance signal level of the reconstructed image, and derives a second value by applying the first value to the modified filter strength setting information.

[0050] A computer can be suitably used to function as the above-mentioned encoding device 1, and such a computer can be realized by storing in a storage unit of the computer a program describing the processing contents for realizing each function of the encoding device 1, and having the computer's CPU read and execute this program. Note that this program can be recorded on a computer-readable recording medium.

[0051] (Decoding device) Next, a decoding device according to an embodiment will be described. Fig. 4 is a block diagram showing an example of the configuration of a decoding device according to an embodiment. The decoding device 2 shown in Fig. 4 includes an entropy decoding unit 31, an inverse quantization unit 32, an inverse transform unit 33, an adder unit 34, a deblocking filter unit 35, a sample adaptive offset unit 36, a storage unit 37, an intra prediction unit 38, a motion compensation prediction unit 39, and a switching unit 40. The decoding device 2 decodes the coded data of an input image coded by the coding device 1.

[0052] The entropy decoding unit 31 decodes the coded data output by the coding device 1, and obtains the quantization coefficient, the intra prediction mode, the motion prediction information, the information on the filter, and the information on the sample adaptive offset. Then, the entropy decoding unit 31 outputs the quantization coefficient to the inverse quantization unit 32, outputs the intra prediction mode to the intra prediction unit 38, outputs the motion prediction information to the motion compensation prediction unit 39, outputs the information on the filter to the deblocking filter unit 35, and outputs the information on the sample adaptive offset to the sample adaptive offset unit 36.

[0053] The inverse quantization unit 32 inputs the quantization coefficients and quantization parameters from the entropy decoding unit 31, multiplies the quantization coefficients by a quantization step derived from the quantization parameter to restore the orthogonal transform coefficients for each block, and outputs the orthogonal transform coefficients to the inverse transform unit 33.

[0054] The inverse transform unit 33 performs inverse transform on the orthogonal transform coefficients input from the inverse quantization unit 32 to generate a residual image, and outputs the residual image to the addition unit .

[0055] The adder 34 adds each pixel value of the residual image input from the inverse transformer 33 and the predicted image input from the switching unit 40 to generate a reconstructed image, and outputs the reconstructed image to the deblocking filter unit 35.

[0056] The deblocking filter unit 35 performs filtering on the reconstructed image input from the adder unit 34, and outputs the filtered reconstructed image to the sample adaptive offset unit 36. The deblocking filter unit 35 controls the filter strength according to the luminance signal level (pixel value of the luminance component) of the reconstructed image and the quantization parameter.

[0057] The sample adaptive offset unit 36 ​​adds an offset to the image input from the deblocking filter unit 35 in accordance with the sample adaptive offset information input from the entropy decoding unit 31, and outputs the result to the memory unit 37 as a decoded image.

[0058] The storage unit 37 stores one frame of image, and outputs the stored image to the outside of the decoding device 2.

[0059] The intra prediction unit 38 refers to the decoded image stored in the memory unit 37, performs prediction processing according to the intra prediction mode input from the entropy decoding unit 31 to generate an intra prediction image, and outputs the intra prediction image to the switching unit 40.

[0060] The motion compensation prediction unit 39 refers to the decoded image stored in the memory unit 37, performs prediction processing according to the motion vector information input from the entropy decoding unit 31 to generate a motion compensation prediction image, and outputs the motion compensation prediction image to the switching unit 40.

[0061] The switching unit 40 switches between the intra-predicted image input from the intra-prediction unit 38 and the motion-compensated predicted image input from the motion-compensated prediction unit 39, and outputs the intra-predicted image or the motion-compensated predicted image to the addition unit 34.

[0062] The image decoding unit 30 is made up of the inverse quantization unit 32, the inverse transform unit 33, the addition unit 34, the intra prediction unit 38, the motion compensation prediction unit 39, and the switching unit 40. As described above, the image decoding unit 30 reconstructs orthogonal transform coefficients from the quantization coefficients based on the quantization parameter, and generates a reconstructed image by performing an inverse orthogonal transform on the orthogonal transform coefficients and adding a predicted image of the decoded image to the reconstructed residual image.

[0063] The process of the deblocking filter unit 35 is the same as that of the deblocking filter unit 18. That is, the deblocking filter unit 35 adjusts the thresholds β′ and t C By shifting ', Q av It is possible to adaptively control the threshold value for switching the filter strength according to the threshold values ​​β' and t C ' to the right, the thresholds β and t CSince the value of increases, it becomes easier to satisfy the above conditional expressions (2) to (7), and it becomes easier to apply a strong filter. Therefore, in the decoding device 2 according to the present invention, when the luminance signal level L is high, it becomes easier to apply a strong filter in the deblocking filter unit 35, and as a result, it is possible to reduce the occurrence of block distortion without impairing the compression effect.

[0064] In this way, in the decoding device 2, the deblocking filter unit 35 controls the filter strength in accordance with the luminance signal level of the reconstructed image and the quantization parameter. In one embodiment, the deblocking filter unit 35 controls the filter strength in accordance with the first value (Q av ) and the second value (β, t C ) and holds filter strength setting information (reference table) indicating a correspondence relationship between the quantization parameters of the first and second blocks. The deblocking filter unit 35 modifies the filter strength setting information according to the luminance signal level of the reconstructed image, and derives a second value by applying the first value to the modified filter strength setting information. The first value is a value determined by the average value of the quantization parameters of two adjacent blocks in the reconstructed image. The second value is a value that functions as a threshold for switching the filter strength. The deblocking filter unit 35 switches the filter strength using the second value.

[0065] In one embodiment, the deblocking filter unit 35 controls the filter strength according to a format that defines the dynamic range of the luminance value of the input image. The deblocking filter unit 35 holds filter strength setting information (reference table) indicating a correspondence relationship between a first value calculated from the quantization parameter and a second value that determines the filter strength, and modification information (see formula (10)) that defines a modification method of the filter strength setting information for each format. The deblocking filter unit 35 specifies a modification method corresponding to the format applied to the input image based on the modification information, modifies the filter strength setting information according to the luminance signal level of the reconstructed image using the specified modification method, and derives a second value by applying the first value to the modified filter strength setting information.

[0066] A computer can be suitably used to function as the above-mentioned decoding device 2, and such a computer can be realized by storing in a storage unit of the computer a program describing the processing contents for realizing each function of the decoding device 2, and having the CPU of the computer read and execute this program. Note that this program can be recorded on a computer-readable recording medium.

[0067] Although the above-mentioned embodiment has been described as a representative example, it is obvious 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 interpreted as being limited by the above-mentioned embodiment, and various modifications and changes are possible without departing from the scope of the claims. For example, it is possible to combine multiple building blocks shown in the configuration diagram of the embodiment into one, or to divide one building block.

[0068] This application claims priority from Japanese Patent Application No. 2016-230524 (filed November 28, 2016) and Japanese Patent Application No. 2017-23345 (filed February 10, 2017), the contents of which are incorporated herein in their entirety. [Explanation of symbols]

[0069] 1 Encoding device 2. Decryption device 10 Image Decoding Unit 11 Block division section 12 Subtraction section 13 Conversion section 14 Quantization section 15 Inverse quantization section 16 Reverse conversion section 17 Addition section 18 Deblocking filter section 19 Sample Adaptive Offset Section 20 Memory section 21 Intra prediction unit 22 Motion compensation prediction unit 23 Switching section 24 Entropy coding unit 30 Image Decoding Unit 31 Entropy Decoding Unit 32 Inverse quantization section 33 Reverse conversion section 34 Addition section 35 Deblocking filter section 36 Sample Adaptive Offset Section 37 Memory section 38 Intra Prediction Unit 39 Motion compensation prediction unit 40 Switching section

Claims

1. A decoding device, comprising: The present invention includes an acquisition means for acquiring a bitstream including quantized coefficients obtained by quantizing transform coefficients of blocks obtained by dividing an image and a sequence parameter set which is a high-level syntax, the decoding device sets one or more thresholds to be used in a deblocking filter process for the block, using the sequence parameter set acquired by the acquisition means; The decoding device generates a reconstructed image using the quantization coefficients acquired by the acquisition means; The decoding device sets the one or more thresholds using the sequence parameter set acquired by the acquisition means, identifies a luminance signal level range to which the luminance signal level belongs by comparing a luminance signal level in the reconstructed image with the one or more thresholds, and determines parameters for controlling the deblocking filter process using an adjustment value associated with the identified luminance signal level range. Decryption device.

2. A computer is caused to function as the decoding device according to claim 1. program.

Images