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EP-4742667-A1 - INTERACTION OF QUANTIZATION CONSTRAINED CORRECTION WITH ZEROING-OUT OF COEFFICIENTS

EP4742667A1EP 4742667 A1EP4742667 A1EP 4742667A1EP-4742667-A1

Abstract

Method and apparatus are described wherein a filtered reconstructed image block from a prediction block and a reconstructed prediction residual is obtained and a Quantization Constrained correction is applied to the filtered reconstructed image block, wherein the Quantization Constrained correction applied depends on whether at least one part of transformed coefficients decoded for the image block have been zeroed out during encoding of the image block. In some embodiments, QC correction is skipped for these transformed coefficients. In some variants, scanning of the transformed coefficients is adapted for the image block.

Inventors

  • LE PENDU, Mikael
  • BORDES, PHILIPPE
  • NASER, Karam

Assignees

  • InterDigital CE Patent Holdings, SAS

Dates

Publication Date
20260513
Application Date
20241108

Claims (15)

  1. A method comprising: obtaining a filtered reconstructed image block from a prediction block and a reconstructed prediction residual; applying a Quantization Constrained correction to the filtered reconstructed image block, wherein the Quantization Constrained correction applied depends on whether at least one part of transformed coefficients decoded for the image block have been zeroed out during encoding of the image block.
  2. The method of claim 1, wherein determining that at least one part of transformed coefficients decoded for the image block have been zeroed out during encoding of the image block comprises at least one of: the image block is coded in a skip mode, a coded block flag is decoded for the image block with a zero value, the image block is coded using a non-separable transform LFNST or NSPT, the image block is coded using a subblock transform (SBT) mode, or the transform block is a large block having a width or a height higher than a given size.
  3. The method of claim 1 or 2, wherein applying the Quantization Constrained correction to the filtered reconstructed image block comprises: obtaining at least one transform coefficient from a prediction residual determined between the filtered reconstructed image block and the prediction block, correcting the at least one transform coefficient, when the at least one transform coefficient is not between an inferior quantization bound and a superior quantization bound, the inferior quantization bound, and the superior quantization bound being associated to a quantization level decoded for the at least one transform coefficient.
  4. The method of claim 3, wherein in response to determining that at least one part of transformed coefficients decoded for the image block have been zeroed out during encoding of the image block, correcting the at least one transform coefficient is skipped for the at least one part of transformed coefficients decoded for the image block that have been zeroed out.
  5. The method of claim 4, wherein skipping the correction is made by adapting a scanning order of the block.
  6. The method of claim 5, wherein only non-zeroed-out transform coefficients are scanned and corrected.
  7. The method of claim 3, wherein in response to determining that at least one part of transformed coefficients decoded for the image block have been zeroed out during encoding of the image block and that the filtered reconstructed image block has been obtained using a partial inverse transform, a full transform and a full inverse transform is used when applying the Quantization Constrained correction to the filtered reconstructed image block.
  8. The method of any one of claims 3 or 5-6, wherein when the Quantization Constrained correction is applied using an inverse transform on a difference between the transform coefficient and the corrected transform coefficient, in response to determining that at least one part of transformed coefficients decoded for the image block have been zeroed out during encoding of the image block, correcting the at least one transform coefficient is performed by setting the difference to 0.
  9. The method of claim 8, wherein partial forward and partial inverse transform is used for applying the Quantization Constrained correction.
  10. The method of claim 1, wherein, for an image block for which all decoded quantization levels are 0, the Quantization Constrained correction is performed using a default transform and a corresponding inverse transform.
  11. The method of any one of claims 1-10, comprising encoding the image block.
  12. The method of any one of claims 1-10, comprising decoding the image block.
  13. An apparatus comprising one or more processors configured to implement the method of any one of claims 1-12.
  14. A computer program product including instructions for causing one or more processors to carry out the method of any of claims 1-12.
  15. A non-transitory computer readable medium storing executable program instructions to cause a computer executing the instructions to perform a method according to any of claims 1-12.

Description

BACKGROUND The present application is related to video compression. The present embodiments relate to a method and an apparatus for encoding or decoding an image or a video. More particularly, the present embodiments relate to in-loop or out-of-loop filters and quantization. To achieve high compression efficiency, image and video coding schemes usually employ prediction and transform to leverage spatial and temporal redundancy in the video content. Generally, intra or inter prediction is used to exploit the intra or inter picture correlation, then the differences between the original block and the predicted block, often denoted as prediction errors or prediction residuals, are transformed, quantized, and entropy coded. In inter prediction, motion vectors used in motion compensation are often predicted from motion vector predictor. To reconstruct the video, the compressed data are decoded by inverse processes corresponding to the entropy coding, quantization, transform, and prediction. BRIEF SUMMARY Briefly stated, in one embodiment, a method for image block encoding or decoding is provided; The method comprises obtaining a filtered reconstructed image block from a prediction block and a reconstructed prediction residual and applying a Quantization Constrained correction to the filtered reconstructed image block, wherein the Quantization Constrained correction applied depends on whether at least one part of transformed coefficients decoded for the image block have been zeroed out during encoding of the image block. In another embodiment, an apparatus for image block encoding or decoding is provided wherein the apparatus comprises one or more processors configured to obtain a filtered reconstructed image block from a prediction block and a reconstructed prediction residual and apply a Quantization Constrained correction to the filtered reconstructed image block, wherein the Quantization Constrained correction applied depends on whether at least one part of transformed coefficients decoded for the image block have been zeroed out during encoding of the image block. In another aspect, a computer program product and a non-transitory computer readable medium storing executable program instructions to cause a computer executing the program instructions to perform the method mentioned above according to any one of the embodiments described herein is provided. BRIEF DESCRIPTION OF THE DRAWINGS The following detailed description will be better understood when read in conjunction with the appended drawings, in which there are shown examples of one or more of the multiple embodiments of the present disclosure. It should be understood, however, that the embodiments described herein are not limited to the precise arrangements and instrumentalities shown in the drawings. In the drawings: FIG. 1 is a block diagram illustrating an example system according to one or more embodiments of the present disclosure;FIG. 2 is a block diagram illustrating an example video encoder according to one or more embodiments of the present disclosure;FIG. 3 is a block diagram illustrating an example video decoder according to one or more embodiments of the present disclosure;FIG. 4 illustrates an example of quantization and dequantization of a transform coefficient;FIG. 5 illustrates an example of quantization bounds and reconstruction values;FIG. 6 illustrates an example of reconstruction of a block with filtering;FIG. 7 illustrates an example of quantization-constrained correction;FIG. 8 illustrates an example of a projection function onto the quantization constraint;FIG. 9 illustrates an example of a smooth correction function;FIG. 10 illustrates an example of differential QC correction from residual block;FIG. 11 illustrates an example of Low-Frequency Non-Separable Transform (LFNST) process;FIG. 12 illustrates an example of NSPT applied to small block, while LFNST is applied for the other block sizes;FIG. 13 illustrates an example of SBT position, type and transform type;FIG. 14 illustrates an example of partial transform for a 64x64 block;FIG. 15 illustrates an example of a diagonal scan per groups of 4x4 coefficients;FIG. 16 illustrates an example of partial LFNST transform;FIG. 17 illustrates an example of partial inverse LFNST transform;FIG. 18 illustrates a block diagram of a QC correction of transform coefficients with adapted scanning for cases of partial zero-out;FIG. 19 illustrates an example of a raster scan (left) and diagonal scan (right) based on the full width W and height H of a large transform with zero-out of high frequency coefficients, according to an embodiment;FIG. 20 illustrates an example of a raster scan (left) and diagonal scan (right) based on the width W_lf and height H_lf of the subblock of non-zeroed-out coefficients in a large transform block, according to an embodiment;FIG. 21 illustrates an example of a full LFNST transform;FIG. 22 illustrates an example of a full LFNST inverse transform;FIG. 23 illustrate