WO2014107885A1

WO2014107885A1 - An efficient coding method for dlt in 3dvc

Info

Publication number: WO2014107885A1
Application number: PCT/CN2013/070377
Authority: WO
Inventors: Kai Zhang; Jicheng An
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2013-01-11
Filing date: 2013-01-11
Publication date: 2014-07-17

Abstract

In the current HTM, A Depth Lookup Table (DLT) is adopted to improve the intra-coding efficiency for depth-map. All values in DLT are coded with Exp-Golomb codes, which take more than 65% bits in SPS averagely. This contribution proposes an efficient coding method for DLT in 3DVC. By applying a Range Constrained Bit Map (RCBM) coding method, the average number of bits required by DLT can be reduced significantly.

Description

AN EFFICIENT CODING METHOD FOR DLT IN 3DVC

FIELD OF INVENTION

The invention relates generally to Three-Dimensional (3D) video processing. In particular, the present invention relates to improvement on Depth Lookup Table (DLT) coding.

BACKGROUND OF THE INVENTION

Simplified Depth Coding (SDC) and a Depth Lookup Table (DLT) are adopted into HTM. For each CU, if SDC mode is selected, there is only a set of four different prediction modes available. After having selected the optimal prediction modes among the four, the resulting residual is not coded using transform. As the SDC prediction stage always results in one or two depth segments per coded block, a single residual DC depth value is coded for each of these segments. Moreover, DLT is used to map coded depth values in SDC to valid depth values of the original depth map. The DLT is constructed based on an initial analysis of the input depth map and is then coded in SPS.

DLT is an optional coding tool. In the current HTM, the encoder will not use DLT if all values from 0 to MAX_DEPTH_VALUE (e.g. 255) appear in original depth map at the analysis step. Otherwise, DLT will be coded in SPS. Figure 1 illustrates an example of DLT. In order to code DLT, the number of valid depth values is coded with Exp-Golomb code first. Then each valid depth value is coded also with Exp-Golomb code as depicted in Table 1.

Exp-Golomb code is efficient when smaller values possess higher probabilities of occurrence. However, that is not the case for valid depth values and the number of valid depth values. As a result, Exp-Golomb codes usually have long code-lengths thus DLT requires a large amount of coding bits. In the common test condition, four sequences Balloons, Kendo, Newspapercc and PoznanHall are determined to use DLT, while the other three are not. Statistics are done on the four sequences. As depicted in Table 2, DLT requires 557.33 bits in average, which account for more than 65% bits of SPS in depth components. In other words, the DLT coding makes SPS in depth components much larger than the one without DLT. Table 1 DLT coding method in the current HTM.

Table 2 Number of bits in DLT and SPS in the current HTM.

SUMMARY OF THE INVENTION

In light of the previously described problems, an efficient coding method for DLT in

3DVC is proposed. It is proposed to code DLT using a Range Constrained Bit Map (RCBM) coding method. The proposed method can reduce the number of bits required by DLT significantly.

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 THE 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 an example of DLT. There are five valid values appears in depth samples at the analysis step. Therefore, there are five items in DLT in the order: 50, 108, 110, 112 and 200;

Fig. 2 is a diagram illustrating an example of the proposed coding 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.

To code the DLT more efficiently, a Range Constrained Bit Map (RCBM) coding method is proposed. With RCBM, DLT is coded in two steps.

First, min_table_value and diff_max_value are coded as unsigned integer to constrain the value range of DLT. The smallest value in DLT is min_table_value and the largest is max_table_value, which equals to min_table_value + diff_max_value.

Then, the bit map is coded. bit_map_flag[i], with i= 0, ... (max_table_value - min_table_value - 2) compose the bit map. If bit_map_flag [i] =1, then depth value (i + min_table_value + 1) belongs to DLT. Otherwise, i.e., bit_map_flag [i] =0, depth value (i + min_table_value + 1) does not belong to DLT.

A flag full_map_flag is used to signal whether to code min_table_value and diff_max_value or not. When the range is not coded, min_table_value = -1, max_table_value = MAX_DEPTH_VALUE+1 and a full bit map without range constrained is coded. Obviously, the full bit map requires MAX_DEPTH_VALUE + 1 bits. The encoder can decide whether to code the range or not depending on which requires fewer bits. Hence, the proposed method requires MAX_DEPTH_VALUE + 2 (e.g. 257 for 8-bit samples) bits at most.

Fig.2 shows an example of how the proposed method works.

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.

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.

Table 3 the proposed DLT coding method. code_fu ll_b it_m ap _fla g [i] u(l) if ( ! code_fu ll_b it_m ap_flag[i]){

min_dlt_value[i] u(v) diff_max_dlt_value[i] u(v)

}

for(j=0;j< max_dlt_value[i] - min_dlt_value[i] - l;j++)

b it_m ap _fla g [i] [j ] u(l)

Claims

1. A method of coding a lookup table for depth intra-coding, which records specific integer values in order.

2. The method as claimed in claim 1, wherein the lookup table is used for depth intra- coding in three-dimensional video coding (3DVC), and the lookup table can is Depth Lookup Table (DLT) in 3DVC.

3. The method as claimed in claim 1, wherein a smallest value min_table_value in the lookup table is coded.

4. The method as claimed in claim 3, wherein min_table_value is coded as a integer or unsigned integer with n bits, where n = |^~log₂ (MAX _ VALUE + 1)^~| .

5. The method as claimed in claim 1, wherein a largest value max_table_value in the lookup table is coded explicitly or inferred implicitly.

6. The method as claimed in claim 1, wherein a difference between a largest value and a smallest value diff_max_value in the lookup table is coded.

7. The method as claimed in claim 6, wherein diff_max_value is coded as a integer or unsigned integer with n bits, where n = |^~log₂ (MAX _ VALUE + 1 - min _ table _ value )^~| .

8. The method as claimed in claim 5, max_table_value is computed as max_table_value= min_table_value+ diff_max_value.

9. The method as claimed in claim 3, wherein a flag full_map_falg is coded to signal whether min_table_value and diff_max_value is coded or not.

10. The method as claimed in claim 8, wherein min_table_value and max_table_value are set to default values when min_table_value and diff_max_value are not coded.

11. The method as claimed in claim 10, wherein the default value of min_table_value is -1 and the default value of max_table_value is MAX_VALUE+1.

12. The method as claimed in claim 1, wherein a bit map is coded; and the bit map is composed of a series of flags bit_map_flag[i], with i= 0, ... (max_table_value - min_table_value

- 2).

13. The method as claimed in claim 12, wherein the bit map is composed of a series of flags bit_map_flag[i], with i= 0, ... MAX_VALUE if min_table_value and max_table_value are not coded.

14. The method as claimed in claim 12, wherein the value equaling to (i + min_table_value + 1) is one item in the lookup table if bit_map_flag[i] =1; and value equaling to (i + min_table_value + 1) is not one item in the lookup table if bit_map_flag[i] =0.

15. The method as claimed in claim 12, wherein the value equaling to (i + min_table_value + 1) is one item in the lookup table if bit_map_flag[i] =0; and value equaling to (i + min_table_value + 1) is not one item in the lookup table if bit_map_flag[i] =1.