WO2015089693A1

WO2015089693A1 - Approximation method for division operation

Info

Publication number: WO2015089693A1
Application number: PCT/CN2013/089482
Authority: WO
Inventors: Kai Zhang; Jicheng An; Xianguo Zhang
Original assignee: MediaTek Singapore Pte Ltd
Current assignee: MediaTek Singapore Pte Ltd
Priority date: 2013-12-16
Filing date: 2013-12-16
Publication date: 2015-06-25
Anticipated expiration: 2016-06-16

Abstract

This contribution presents an approximation method for division operation. It is proposed to utilize operations of multiplication, addition (subtraction), shift and comparison to replace the division operation.

Description

APPROXIMATION METHOD FOR DIVISION OPERATION

TECHNICAL FIELD

[0001] The invention relates generally to approximation for division operation. In particular, the presented invention relates to depth coding method in three-Dimensional (3D) video processing. BACKGROUND

[0002] In the current 3D-HEVC (JCT3V-F1005), samples in the depth component are used to derive disparity vectors for texture component coding. A disparity vector (DVx, 0) can be derived from its corresponding depth value (dep) by a linear relationship as

DVx = wdep + b , (1)

[0003] where w and b are two camera parameters. In 3D-HEVC, (1) is implemented in an integer form thus w and b can be transmitted from the encoder to the decoder as integers.

[0004] A disparity derived depth (DDD) coding method is proposed to improve the coding efficiency for the depth component as proposed in . It can be seen from (1) that the conversion between a depth value dep and DVx is reversible. Thus, a depth value can also be derived from its corresponding disparity vector (DVx, DVy) as dep =— -DVx -- (2)

w w

[0005] When the collocated texture block of the current depth block is predicted by disparity- compensated prediction (DCP), a DDD candidate will be inserted into the merging candidate list right after the texture candidate. In a DDD candidate, all prediction samples in the current block are set as dep calculated by (2), which is implemented in an integer form. Fig. 1 shows the procedure to derive a depth value from its corresponding disparity vector. It should be noted that the DDD candidate is invalid on the base view since DCP is applied only on dependent views.

[0006] DDD involves division operations as revealed in (2). Since division is a high-cost operation and there is even no divider in some hardware design for video encoder/decoder, the division operation hampers the application of DDD. SUMMARY

[0007] In light of the previously described problems, an approximation method for division operation is invented. It is proposed to utilize operations of multiplication, addition, subtraction, shift, comparison, or any combination thereof to replace the division operation.

[0008] Other aspects and features of the invention will become apparent to those with ordinary skill in the art upon review of the following descriptions of specific embodiments.

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:

[0009] Fig. 1 is a diagram illustrating a depth value derived from its corresponding disparity vector.

DETAILED DESCRIPTION

[0010] 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.

[0011] All variables in the following discussion are integers. And 2^M should be calculated as l« in implementation.

[0012] In the first exemplary embodiment, Equation (2) is approximated without the division operation.

[0013] In the first step, (2) is rewritten as

1 b

dep = sign(w)(-.— ?*DVx - -.—) . (3)

w\ w\

[0014] It is obvious that

[0015] Denote Ω = [log₂ |w|J . In practical, Ω can be obtained following the C-style pseudo codes as: Ω=0;

while( ((( 1 « Ω) « 1 ) <= |w| ) )

Ω++;

[0016] Thus

2^Ω<|ιν|<2^Ω+1 (5)

[0017] Therefore, for k satisfying

2^M < k≤ 2^M+l , (6)

it can be derived that

[0018] For k from 2^Mto 2^M+1 inclusively, there must be one k making k\w\ approaching 2^M+n+l mostly. Such a k, denoted as a, can be obtained following the C-style pseudo codes as:

a = 2

for(k=2^M;k<=2^M+1;k++)

if(\k\w\-2^M+n+l\<E_imn){

E_mm = \k\w\-2^M+n+l\

a = k;

}

[0019] Therefore, (4) can be derived as

( .

[0020] (8) can be calculated without division operations as

a-DVx-ab _¾ (_a._DVx__{ab +} p₎ » ( + Ω + 1) , (9)

>Μ+Ω+1

where β is an offset value.

[0021] In the first embodiment, β is set equal to 1«( Μ+Ω).

[0022] In the second embodiment, β is set equal to (1«( +Ω))+ yQ), where

[0023] Q is a positive integer. In one embodiment, Q is set equal to (1«( +Ω-4).

[0024] From (3) and (9), (2) can be calculated approximately without a division as

dep * sign(w)[(a-DVx - ab + β) » (M + Ω + 1)] , (9) [0025] In the second exemplary embodiment, the precision of w and b considered. For example, (1) is rewritten as

DVx = (wdep + (b « q) + offset) » (p + q) , (11)

where p is the precision of w and b, q is the bit-depths of dep samples, which is 8 usually. Offset is set equal to \«{p + -l).

[0026] It can be derived from (11) that

2^p+q 2^qb 1 b '

dep = - DVx -— = -'DVx'-— (12)

W W W w

Where DVx '= 2^p+q DVx and b '=2^q b.

[0027] Following the same method in the first exemplary embodiment, (12) can be calculated approximately without a division as

dep « sign(w)[(ceDVx'- ab '+ β) » (M + Ω + 1)]

= sign(w)[((a « (p + q))»DVx - (a « q) + β) » (M + Ω + 1)] ^'

[0028] The proposed method described above can be used in a video encoder as well as in a video decoder. Embodiments of 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.

[0029] 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

1. A method of making approximation for integer division operation, comprising utilizing operations of multiplication, addition, subtraction, shift, comparison, or any combination thereof to replace a division operation.

2. The method as claimed in claim 1 , wherein Ω = [log₂ |w|J is calculated.

3. The method as claimed in claim 2, wherein k with minimal \k\w\ - 2^S\ is found, denoted as a, where k is a positive integer.

4. The method as claimed in claim 3, wherein S is a positive integer greater than Ω.

5. The method as claimed in claim 4, wherein S is equal to +Ω + 1 and k is searched from a range of [2^M +1,

6. The method as claimed in claim 5, wherein is a positive integer.

7. The method as claimed in claim 3, wherein b/w is approximated by sign(w)-((a-6+ ?)>> S).

8. The method as claimed in claim 7, wherein β is set equal to 1«(S-1).

9. The method as claimed in claim 7, wherein β is larger than 1«(S- 1) if a\w\ - 2^S<Q; β is lower than 1«(S-1) if a\w\ - 2^S>0; β is equal to 1«(S- 1) if a\w\ - 2^S=0.

10. The method as claimed in claim 7, wherein β is set equal to (1«(S-1))+ .

1 1. The method as claimed in claim 7, wherein P is positive if a\w\ - 2^S<Q; P is negative if a\w\

12. The method as claimed in claim 2, wherein the approximation method works in different ways depending on whether w is equal to 2^Ω or not.

13. The method as claimed in claim 12, wherein b/w is approximated by (¾+(1«( Ω-1))>> Ω, if w is equal to 2^Ω.

14. The method as claimed in claim 1 , wherein the approximation method for integer division operation is utilized in a video coding system.

15. The method as claimed in claim 14, wherein the approximation method for integer division operation is utilized in 3D video coding system.