WO2016037363A1

WO2016037363A1 - Methods of residue transform tree representation

Info

Publication number: WO2016037363A1
Application number: PCT/CN2014/086426
Authority: WO
Inventors: Jicheng An; Kai Zhang
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2014-09-12
Filing date: 2014-09-12
Publication date: 2016-03-17

Abstract

Method of residue transform tree representation for color components including Y, U, and V components is disclosed. The Y, U, and V components are not forced to have the same residue transform depth.

Description

METHODS OF RESIDUE TRANSFORM TREE REPRESENTATION

TECHNICAL FIELD

The invention relates generally to video processing. In particular, the present invention relates to methods and apparatuses for residue transform tree representation for Y, U, and V components in High Efficiency Video Coding (HEVC) .

BACKGROUND

HEVC is an advanced video coding system developed under the Joint Collaborative Team on Video Coding (JCT-VC) group of video coding experts from ITU-T Study Group. In HEVC, the residue transform depth is shared between luma (Y) and chroma (U and V) components. In transform tree syntax, a syntax element split_transform_flag is used to indicate the transform depth increase for all Y, U, and V components as shown in Fig. 1. In CU level, the transform tree coding (including transform split flag, cbf and coefficients) signals the residual of Y, U, V components together as shown in Fig. 2. In Sequence Parameter Set RBSP (SPS) syntax, a syntax element max_transform_hierarchy_depth_inter is used to indicate the maximum transform depth in a sequence for all Y, U, and V components for inter case, and a syntax element max_transform_hierarchy_depth_intra is used to indicate the maximum transform depth in a sequence for all Y, U, and V components for intra case.

However, there is no evidence to show that the Y, U, and V components have dependencies in residue transform depth. Therefore, applying the same transform depth on Y, U, and V components may hurt coding performance.

SUMMARY

In light of the previously described problems, there exists a need for an apparatus and method, in which the Y, U, and V components are not forced to have the same residual transform depth.

In one embodiment, in transform tree syntax, three separate syntax elements split_transform_Y_flag, split_transform_U_flag, and split_transform_V_flag instead of one shared split_transform_flag, are used to indicate the transform depth increase for Y, U, and V components respectively as shown in Fig. 3. The transform tree coding for Y, U, and V components are shown in Fig. 4, Fig. 5, and Fig. 6 respectively. In CU level, the transform tree is signaled separately for each component and with the Y components signaled at the last. For example, first, the transform tree for U component is signaled, then the transform tree for V component is signaled, and finally the transform tree for Y component is signaled.

In another embodiment, in transform tree syntax, two separate syntax elements split_transform_luma_flag, and split_transform_chroma_flag instead of one shared split_transform_flag, are used to indicate the transform depth increase for luma and chroma components respectively as shown in Fig. 7. The transform tree coding for luma component is shown in Fig. 8. The transform tree coding for chroma component is shown in Fig. 9. In CU level, the transform tree for chroma is signaled first, and then the transform tree for luma is signaled.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

Fig. 1 is a diagram illustrating the TU split in HEVC.

Fig. 2 is a flowchart illustrating the transform tree coding in HEVC.

Fig. 3 is a diagram illustrating the TU split in the first embodiment of the proposed method.

Fig. 4 is a flowchart illustrating the transform tree coding for Y component in the first embodiment of the proposed method.

Fig. 5 is a flowchart illustrating the transform tree coding for U component in the first embodiment of the proposed method.

Fig. 6 is a flowchart illustrating the transform tree coding for V component in the first embodiment of the proposed method.

Fig. 7 is a diagram illustrating the TU split in the second embodiment of the proposed method.

Fig. 8 is a flowchart illustrating the transform tree coding for luma component in the second embodiment of the proposed method.

Fig. 9 is a flowchart illustrating the transform tree coding for chroma component in the second embodiment of the proposed method.

DETAILED DESCRIPTION

The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.

It is proposed that the Y, U, and V components are not forced to have the same residual transform depth.

In the first embodiment, in transform tree syntax, three separate syntax elements split_transform_Y_flag, split_transform_U_flag, and split_transform_V_flag instead of one shared split_transform_flag, are used to indicate the transform depth increase for Y, U, and V components respectively as shown in Fig. 3.

In the first embodiment, in CU level, the transform tree is signaled separately for Y, U, V component, and with the Y component signaled at the last, i.e., the transform tree can be signaled as U first, then V, and finally Y, or can be signaled as V first, then U, and finally Y. The transform tree coding for Y, U, and V components are shown in Fig. 4, Fig. 5, and Fig. 6 respectively.

In the first embodiment, for the transform tree coding for Y component as shown in Fig. 4, the transform split flag is signaled in each transform unit level, and the cbf is only signaled in the leaf transform unit level when there is no further transform unit split.

In the first embodiment, for the transform tree coding for U and V components as shown in Fig. 5 and Fig. 6, the transform split flag is signaled after the cbf in each transform unit level. The benefit is that for inter-coded CU, if the cbf is signaled as zero, then the transform split flag can be avoid.

In the second embodiment, in transform tree syntax, two separate syntax elements split_transform_luma_flag and split_transform_chroma_flag instead of one shared split_transform_flag are used to indicate the transform depth increase for luma and chroma components respectively as shown in Fig. 7.

In the second embodiment, in CU level, the transform trees for luma and chroma are signaled separately, and the transform tree for chroma components is signaled before the transform tree for luma component. The transform tree coding for luma and chroma components are shown in Fig. 8, and Fig. 9 respectively.

In the second embodiment, for the transform tree coding for luma component as shown in Fig. 8, the transform split flag is signaled in each transform unit level, and the cbf is only signaled in the leaf transform unit level when there is no further transform unit split.

In the first embodiment, for the transform tree coding for chroma components as shown in Fig. 9, the transform split flag is signaled after the cbfU and cbfV in each transform unit level. The benefit is that for inter-coded CU, if the cbfU and cbfV are both signaled as zero, then the transform split flag can be avoid.

In the third embodiment, in SPS (sequence parameter set) or PPS (picture parameter set) , or slice header syntax, 3 separate syntax elements max_transform_hierarchy_depth_Y_inter, max_transform_hierarchy_depth_U_inter, and max_transform_hierarchy_depth_V_inter instead of one shared syntax element max_transform_hierarchy_depth_inter, are used to indicate the maximum transform depth in a sequence for Y, U, and V components respectively for inter case. 3 separate syntax elements max_transform_hierarchy_depth_Y_intra, max_transform_hierarchy_depth_U_intra, and max_transform_hierarchy_depth_V_intra, instead of one shared syntax element max_transform_hierarchy_depth_intra, are used to indicate the maximum transform depth in a sequence for Y, U, and V components respectively for intra case.

In the fourth embodiment, in SPS, or PPS, or slice header syntax, 2 separate syntax elements max_transform_hierarchy_depth_luma_inter and max_transform_hierarchy_depth_chroma_inter instead of one shared syntax element max_transform_hierarchy_depth_inter, are used to indicate the maximum transform depth in a sequence for luma and chroma components respectively for inter case. 2 separate syntax elements max_transform_hierarchy_depth_luma_intra and max_transform_hierarchy_depth_chroma_intra instead of one shared syntax element max_transform_hierarchy_depth_intra, are used to indicate the maximum transform depth in a sequence for luma and chroma components respectively for intra case.

The methods described above can be used in a video encoder as well as in a video decoder. Embodiments of the methods according to the present invention as described above may be implemented in various hardware, software codes, or a combination of both. For example, an embodiment of the present invention can be a circuit integrated into a video compression chip or program codes integrated into video compression software to perform the processing described herein. An embodiment of the present invention may also be program codes to be executed on a Digital Signal Processor (DSP) to perform the processing described herein. The invention may also involve a number of functions to be performed by a computer processor, a digital signal processor, a microprocessor, or field programmable gate array (FPGA) . These processors can be configured to perform particular tasks according to the invention, by executing machine-readable software code or firmware code that defines the particular methods embodied by the invention. The software code or firmware codes may be developed in different programming languages and different format or style. The software code may also be compiled for different target platform. However, different code formats, styles and languages of software codes and other means of configuring code to perform the tasks in accordance with the invention will not depart from the spirit and scope of the invention.

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described examples are to be considered in all respects only as illustrative and not restrictive. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art) . Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

Claims

A method of residue transform depth representation for color components (Y, U, and V components) , comprising encoding or decoding the residue transform depth representation, wherein different transform depths are allowed for the color components.
The method as claimed in claim 1, wherein the Y, U and V components are allowed to use different transform depths.
The method as claimed in claim 2, wherein three transform trees in coding unit (CU) level are signaled for Y, U, and V components respectively.
The method as claimed in claim 3, wherein the signaling order for the three transform tree is that U first, then V, and finally Y； or V first, then U, and finally Y.
The method as claimed in claim 3, in the transform tree for Y component, one split_transform_Y_flag is signaled at each transform unit level to indicate whether the transform unit is split or not for Y component, and at the leaf transform unit level (i.e. , the transform unit is not further split) the cbf_Y (coded block flag) is signaled to indicate whether this transform unit has coefficients or not for Y component.
The method as claimed in claim 3, in the transform tree for U component, the cbf_U is signaled at each transform unit level to indicate whether this transform unit has coefficients or not for U component, and one split_transform_U_flag is signaled after the cbf_Y to indicate whether the transform unit is split or not for U component.
The method as claimed in claim 6, the split_transform_U_flag is not signaled when the cbf_U is equal to 0 for inter-coded block.
The method as claimed in claim 3, in the transform tree for V component, the cbf_V is signaled at each transform unit level to indicate whether this transform unit has coefficients or not for V component, and one split_transform_V_flag is signaled after the cbf_V to indicate whether the transform unit is split or not for V component.
The method as claimed in claim 8, the split_transform_V_flag is not signaled when the cbf_V is equal to 0 for inter-coded block.
The method as claimed in claim 1, wherein the luma (Y) and chroma (U and V) components are allowed to use different transform depths.
The method as claimed in claim 10, wherein two transform trees in CU level are signaled for luma and chroma components respectively.
The method as claimed in claim 11, wherein the signaling order for the two transform tree is that chroma first, and then followed by luma.
The method as claimed in claim 11, in the transform tree for luma component, one split_transform_luma_flag is signaled at each transform unit level to indicate whether the transform unit is split or not for luma component, and at the leaf transform unit level (i. e. , the transform unit is not further split) the cbf_Y (coded block flag) is signaled to indicate whether this transform unit has coefficients or not for luma component.
The method as claimed in claim 11, in the transform tree for chroma component, the cbf_U and cbf_V are signaled at each transform unit level to indicate whether this transform unit has coefficients or not for U and V component respectively, and one split_transform_chroma_flag is signaled after the cbf_U and cbf_V to indicate whether the transform unit is split or not for chroma components.
The method as claimed in claim 14, the split_transform_chroma_flag is not signaled when the cbf_U and cbf_V are both equal to 0 for inter-coded block.
The method as claimed in claim 1, wherein the maximum transform depth for inter case of a sequence or picture or slice can be derived by three syntax elements (such as max_transform_hierarchy_depth_Y_inter, max_transform_hierarchy_depth_U_inter, and max_transform_hierarchy_depth_V_inter) respectively for Y, U, and V components, and the maximum transform depth for intra case of a sequence or picture or slice can be derived by three syntax elements (such as max_transform_hierarchy_depth_Y_intra, max_transform_hierarchy_depth_U_intra, and max_transform_hierarchy_depth_V_intra) respectively for Y, U, and V components.
The method as claimed in claim 1, wherein the maximum transform depth for inter case of a sequence or picture or slice can be derived by two syntax elements (such as max_transform_hierarchy_depth_luma_inter, and max_transform_hierarchy_depth_chroma_inter) respectively for luma and chroma components, and the maximum transform depth for intra case of a sequence or picture or slice can be derived by two syntax elements (such as max_transform_hierarchy_depth_luma_intra, and max_transform_hierarchy_depth_chroma_intra) respectively for luma and chroma components.