MIXED DOMAIN COLLABORATIVE POST FILTER FOR LOSSY STILL IMAGE CODING

• US 20190313124A1
• Filed: 06/21/2019
• Published: 10/10/2019
• Est. Priority Date: 12/23/2016
• Status: Active Grant

• Current Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Inventors: STEPIN, Victor Alexeevich, CHERNYAK, Roman Igorevich, SILANTIEV, Albert Yurievich
• Granted Patent: US 10,965,958 B2
• Time in Patent Office: Days
• CPC Class Codes: G06T 2207/20021 Dividing image into blocks, subimages or windows
• CPC Class Codes: G06T 2207/20048 Transform domain processing
• CPC Class Codes: G06T 5/10 using non-spatial domain filtering
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06T 9/00 Image coding bandwidth or redundancy reduction for static pictures H04N1/41; coding or decoding of static colour picture signals H04N1/64; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00
• CPC Class Codes: H04N 19/117 Filters, e.g. for pre-processing or post-processing sub-band filter banks H04N19/635
• CPC Class Codes: H04N 19/147 according to rate distortion criteria rate-distortion as a criterion for motion estimation H04N19/567
• CPC Class Codes: H04N 19/154 Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion use of rate-distortion criteria H04N19/147
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/19 using optimisation based on Lagrange multipliers
• CPC Class Codes: H04N 19/196 being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters processing of motion vectors H04N19/513
• CPC Class Codes: H04N 19/60 using transform coding
• CPC Class Codes: H04N 19/635 characterised by filter definition or implementation details
• CPC Class Codes: H04N 19/82 involving filtering within a prediction loop
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness

Abstract

An image coding apparatus, comprising an image reconstruction unit configured to reconstruct an image, a parameter determination unit configured to determine one or more filter parameters, based on one or more first parameters which are based on the reconstructed image and one or more second parameters which are based on codec signaling information, and a mixed-domain filtering unit configured to filter in a frequency domain and a pixel domain the reconstructed image based on the determined filter parameters to obtain a filtered image.

Claims

1. An image coding apparatus, comprising:

an image reconstruction unit configured to reconstruct an image,

a parameter determination unit configured to determine one or more filter parameters, based on one or more first parameters which are based on the reconstructed image and one or more second parameters which are based on codec signaling information, and

a mixed-domain filtering unit configured to filter in a frequency domain and a pixel domain the reconstructed image based on the determined filter parameters to obtain a filtered image.

2. The image coding apparatus of claim 1, wherein the parameter determination unit is configured to estimate the original image from the reconstructed image and determine the first parameters based on the estimated original image.

3. The image coding apparatus of claim 1, wherein the parameter determination unit is configured to determine a quantization noise value from the codec signaling information and determine the second parameters based on the derived quantization noise value.

4. The image coding apparatus of claim 3, wherein the parameter determination unit is configured to analytically derive the quantization noise value from a quantization parameter QP of the codec signaling information.

5. The image coding apparatus of claim 1, further comprising an application map unit configured to determine where filtering should be implemented.

6. The image coding apparatus of claim 2, wherein the parameter determination unit is configured to determine the filter parameters by:

partitioning the estimated original image into blocks, and

for each of the blocks;

determining a cluster of patches that are similar to the block,

2D-transforming the cluster of patches to obtain transformed patches, and

determining the first parameters based on the transformed patches.

7. The image coding apparatus of claim 6, wherein the parameter determination unit is configured to determine, for each of the blocks, the filter parameters based on the transformed patches by:

regrouping elements of the transformed patches to obtain a matrix T_i, wherein each row of the matrix T_i comprises frequency components with same spatial frequencies,

transforming the matrix T_i to obtain a transformed matrix tf_vwⁱ, wherein each row of the matrix tf_vwⁱ is a 1D transform of a corresponding row of matrix T_i, and

determining the filter parameters g_v,wⁱ as;

8. The image coding apparatus of claim 1, wherein the mixed-domain filtering unit is configured to, for each of a set of blocks of the reconstructed image:

determine a set of patches that are similar to the block,

2D-transform the patches into frequency domain to obtain frequency-domain patches,

perform collaborative filtering of the frequency-domain patches in frequency domain to obtained filtered transformed frequency-domain patches,

inverse 2D transform the filtered transformed frequency-domain patches in frequency domain to obtain filtered patches, and

perform collaborative filtering of the filtered patches in pixel domain along pixel patches from different sets of patches with the same spatial coordinates.

9. The image coding apparatus of claim 8, wherein the 2D transformation is a Haar wavelet transform.

10. The image coding apparatus of claim 8, wherein the mixed-domain filtering unit is configured to perform, for each of the blocks, the collaborative filtering based on the transformed patches by:

regrouping elements of the transformed patches to obtain a matrix T_i, wherein each row of the matrix T_i comprises frequency components with same spatial frequencies,

transforming the matrix T_i to obtain a transformed matrix t wherein each row of the matrix t f_vwⁱ is a 1D transform of a corresponding row of matrix T_i, and

perform filtering by multiplying each element of matrix t f_vwⁱ, by a filter parameter g (Ω

)_wvⁱ,

wherein Ω

is a column number in matrix t f_vwⁱ and spatial frequencies v, w correspond to a j-th row of matrix t f_vwⁱ.

11. The image coding apparatus of claim 7, wherein the 1D transformation is a Hadamard transform.

12. The image coding apparatus of claim 1, wherein

the adaptive_filtering_flag flag is used to indicate that the mixed-domain filtering unit should be used to filter an image,

the frame_level_usage_flag flag is used to indicate that the entire reconstructed image should be filtered,

the macroblock_size field is used to indicate a macroblock size which should be used for filtering, and/or

the use_filtered_mb_flag flag is used to indicate whether a filtered macroblock should be used.

13. A system comprising an image encoding apparatus according to claim 1 and an image decoding apparatus according to claim 1, wherein the parameter determination unit of the image encoding apparatus is configured to determine the filter parameters in the same way as the parameter determination unit of the image decoding apparatus.

14. A method for still image coding, the method comprising:

reconstructing an image,

determining one or more filter parameters based on one or more first parameters which are based on the reconstructed image and one or more second parameters which are based on codec signaling information, and

filtering in a frequency domain and in a pixel domain the reconstructed image based on the determined filter parameters to obtain a filtered image.

15. A computer-readable storage medium storing program code, the program code comprising instructions that when executed by a processor carry out the method of claim 14.