WO2015006883A1

WO2015006883A1 - Motion vector inheritance techniques for depth coding

Info

Publication number: WO2015006883A1
Application number: PCT/CN2013/000859
Authority: WO
Inventors: Liu He; Ying Chen; Li Zhang
Original assignee: Qualcomm Incorporated
Priority date: 2013-07-18
Filing date: 2013-07-18
Publication date: 2015-01-22

Abstract

This disclosure is related to the coding of three-dimensional (3D) video content, which may include texture views and depth views. More specifically, with the techniques of this disclosure, multiple merge candidates may be derivable from a texture picture for the coding of a depth block. In particular, in various examples associated with encoding or decoding a depth block according to a merge mode or a skip mode, a list of candidates generated for coding the depth block includes at least one texture candidate that is not co-located with the depth block.

Description

MOTION VECTOR INHERITANCE TECHNIQUES FOR DEPTH CODING

TECHNICAL FIELD

[0001] This disclosure relates to video coding and compression, and more specifically, coding techniques that may be used in coding three-dimensional (3D) video.

BACKGROUND

[0002] Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, digital cameras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radio telephones, video teleconferencing devices, and the like. Digital video devices implement video compression techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T

H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), the High Efficiency Video Coding (HEVC) standard presently under development, and extensions of such standards, to transmit, receive and store digital video information more efficiently.

[0003] Video compression techniques perform spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice may be partitioned into video blocks, which may also be referred to as treeblocks, coding units (CUs) and/or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to a reference frames.

[0004] A multi-view coding bitstream may be generated by encoding views, e.g., from multiple perspectives. Multi-view coding may allow a decoder to choose between different views, or possibly render multiple views. Moreover, some three-dimensional (3D) video techniques and standards that have been developed, or are under

development, make use of multiview coding aspects. For example, different views may transmit left and right eye views to support 3D video. Alternatively, some 3D video coding processes may apply so-called multiview plus depth coding. In multiview plus depth coding, a 3D video bitstream may contain not only texture view components, but also depth view components. For example, each view may comprise one texture view component and one depth view component.

BRIEF DESCRIPTION OF DRAWINGS

[0005] FIG. 1 is a diagram showing first-time coding, which may be a decoding order in multi-view coding (MVC).

[0006] FIG. 2 is a diagram showing an MVC prediction structure for multi-view coding, which may be used as an example MVC temporal and inter- view prediction structure.

[0007] FIG. 3 is an illustration showing temporal neighboring blocks that may be used in coding according to a neighboring block-based disparity vector (NBDV) process.

[0008] FIG. 4 is an illustration showing a depth block derivation process from a reference view to perform backwards-warping view synthesis prediction (BVSP).

[0009] FIG. 5 is an illustration showing derivation of an inter- view predicted motion vector candidate for merge/skip mode.

[0010] FIG. 6 is a table showing specification of IOCandldx and IlCandldx in 3D- HEVC.

[0011] FIG. 7 is an illustration showing derivation of a motion vector inheritance (MVI) candidate for depth coding.

[0012] FIG. 8 is an illustration showing a prediction structure of advance residual prediction (ARP).

[0013] FIG. 9 is another illustration showing derivation of an MVI candidate from a bottom-right block, for depth coding.

[0014] FIG. 10 is a block diagram illustrating an example video coding system that may utilize the techniques of this disclosure.

[0015] FIG. 11 is a block diagram illustrating an example video encoder that may implement the techniques of this disclosure.

[0016] FIG. 12 is a block diagram illustrating an example video decoder that may implement the techniques of this disclosure. [0017] FIG. 13 is a flow diagram illustrating a coding technique for coding (i.e., encoding or decoding) a depth block according to a merge mode or skip mode.

[0018] FIG. 14 is a flow diagram illustrating a decoding technique for decoding a depth block according to a merge mode or skip mode.

[0019] FIG. 15 is a flow diagram illustrating an encoding technique for encoding a depth block according to a merge mode or skip mode.

[0020] FIG. 16 is a conceptual illustration showing locations of blocks A_l5 B_l5 B₀, A₀, or B₂ relative to a current block shown in the center.

SUMMARY

[0021] This disclosure is related to the coding of three-dimensional (3D) video content, which may include texture views and depth views. More specifically, with the techniques of this disclosure, multiple merge candidates may be derivable from a texture picture for the coding of a depth block. In particular, in various examples associated with encoding or decoding a depth block according to a merge mode or a skip mode, a list of candidates generated for coding the depth block includes at least one texture candidate that is not co-located with the depth block.

[0022] In one example, this disclosure describes a method of decoding depth data associated with 3D video data. The decoding method comprises generating a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block, and decoding the depth block based on the list.

[0023] In another example, this disclosure describes a method of encoding depth data associated with 3D video data. The encoding method comprises, generating a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block, and encoding the depth block based on the list.

[0024] In another example, this disclosure describes a device that codes (e.g., encodes or decodes) depth data associated with 3D video data. The device comprises a depth processing unit that generates a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block, and codes the depth block based on the list. [0025] In another example, this disclosure describes a non-transitory computer-readable storage comprising instructions that upon execution cause one or more processors to generate a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block, and code the depth block based on the list.

[0026] In another example, this disclosure describes a device that comprises means for generating a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block, and means for coding the depth block based on the list.

[0027] The details of one or more examples of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.

DETAILED DESCRIPTION

[0028] This disclosure describes motion vector inheritance techniques that may be used in coding depth information associated with three-dimensional video (3DV).

Section 1 Brief introduction

[0029] This disclosure is related to the coding of three-dimensional (3D) video content, which may include texture views and depth views. More specifically, with the techniques of this disclosure, multiple merge candidates are derived from a texture picture for the coding of a depth block.

Section 2 Video coding techniques and standards

Section 2.1 Video coding standards

[0030] Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) and Multiview Video Coding (MVC) extensions.

[0031] In addition, there is a new video coding standard, namely High-Efficiency Video Coding (HEVC), being developed by the Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG). The latest Working Draft (WD) of HEVC, and referred to as HEVC WD8 hereinafter, is available from http://phenix.int- evry.fr/ict/doc end user/documents/ 1 1 Shanghai/wg 1 1 /JCTVC-K 1003-v 10.zip.

Section 2.2 Multiview Video Coding

[0032] Multiview video coding (MVC) is an extension of H.264/AVC. The MVC specification (i.e. the extension of H.264/AVC) is briefly discussed in this section. Although the phrase "multi view coding" and the acronym "MVC" may be used to describe the extension of H.264/AVC, the phrase "multi view coding" and the acronym "MVC" may also be used in this disclosure to more broadly refer to any coding standard or technique that makes use of multiple views.

Section 2.2.1 MVC bitstream structure

[0033] A typical MVC decoding order (i.e. bitstream order) is shown in FIG. 1. The decoding order arrangement is referred as time-first coding. Each access unit is defined to contain the coded pictures of all the views for one output time instance. Note that the decoding order of access units may not be identical to the output or display order.

Section 2.2.2 MVC coding structure

[0034] A typical MVC prediction (including both inter-picture prediction within each view and inter- view prediction) structure for multi-view video coding is shown in FIG. 2, where predictions are indicated by arrows, the pointed-to object using the point-from object for prediction reference.

[0035] In MVC, the inter-view prediction is supported by disparity motion

compensation, which uses the syntax of the H.264/AVC motion compensation, but allows a picture in a different view to be used as a reference picture.

[0036] Coding of two views could be supported also by MVC, and one of the advantages of MVC is that an MVC encoder could take more than two views as a 3D video input and an MVC decoder can decode such a multiview representation. So any renderer with MVC decoder may expect 3D video contents with more than two views. Section 2.2.3 MVC inter-view prediction

[0037] In MVC, inter-view prediction is allowed among pictures in the same access unit (i.e., with the same time instance). When coding a picture in one of the non-base views, a picture may be added into a reference picture list, if it is in a different view but with a same time instance.

[0038] An inter- view reference picture can be put in any position of a reference picture list, just like any inter prediction reference picture. When inter- view reference picture is used for motion compensation, the corresponding motion vector is referred to 'Disparity Motion Vector.'

Section 2.3 HEVC techniques

[0039] Some relevant HEVC techniques are discussed in this section.

Section 2.3.1 Reference picture list construction

[0040] Typically a reference picture list construction for the first or the second reference picture list of a B picture includes two steps: reference picture list initialization and reference picture list reordering (modification). The reference picture list initialization is an explicit mechanism that put the reference pictures in the reference picture memory (also known as decoded picture buffer) into a list based on the order of POC (Picture Order Count, aligned with display order of a picture) values. The reference picture list reordering mechanism can modify the position of a picture that was put in the list during the reference picture list initialization to any new position, or put any reference picture in the reference picture memory in any position even the picture doesn't belong to the initialized list. Some pictures after the reference picture list reordering (modification), may be put in a very further position in the list. However, if a position of a picture exceeds the number of active reference pictures of the list, the picture is not considered as an entry of the final reference picture list. The number of active reference pictures of may be signaled in the slice header for each list.

[0041] After reference picture lists are constructed (namely RefPicListO and

RefPicListl if available), a reference index to a reference picture list can be used to identify any reference picture included in the reference picture list. Section 2.3.2 TMVP

[0042] To get a Temporal Motion Vector Predictor (TMVP), firstly a co-located picture is to be identified. If the current picture is a B slice, a collocated_from_10_flag is signaled in slice header to indicate whether the co-located picture is from RefPicListO or RefPicListl.

[0043] After a reference picture list is identified, collocated_ref_idx, signaled in a slice header, is used to identify the picture in the picture in the list.

[0044] A co-located prediction unit (PU) is then identified by checking the co-located picture. Either the motion of the right-bottom PU of the coding unit (CU) containing this PU, or the motion of the right-bottom PU within the center PUs of the CU containing this PU is used.

[0045] When motion vectors identified by the above process are used to generate a motion candidate for AMVP or merge mode, they may need to be scaled based on the temporal location (reflected by POC).

[0046] Note the target reference index of all possible reference picture lists for the temporal merging candidate derived from TMVP is always set to 0 while for AMVP, it is set equal to the decoded reference index

[0047] In HEVC, the SPS includes a flag sps_temporal_mvp_enable_flag and the slice header includes a flag pic_temporal_mvp_enable_flag when

sps_temporal_mvp_enable_flag is equal to 1. When both

pic_temporal_mvp_enable_flag and temporal_id are equal to 0 for a particular picture, no motion vector from pictures before that particular picture in decoding order would be used as a temporal motion vector predictor in decoding of the particular picture or a picture after the particular picture in decoding order.

Section 2.4 HEVC based 3DV

[0048] Currently, a Joint Collaboration Team on 3D Video Coding (JCT-3C) of VCEG and MPEG is developing a 3DV standard based on HEVC, for which part of the standardization efforts includes the standardization of the multiview video codec based on HEVC (MV-HEVC) and another part for 3D Video coding based on HEVC (3D- HEVC). For MV-HEVC, it should be guaranteed that there are only high-level syntax (HLS) changes in it, such that no module in the CU/PU level in HEVC needs to be re- designed and can be fully reused for MV-HEVC. For 3D-HEVC, new coding tools, including those in coding unit/prediction unit level, for both texture and depth views may be included and supported. The latest software 3D-HTM for 3D-HEVC can be downloaded from the following link:

[3D-HTM version 7.0]:

https://hevc.hhi.fraunhofer.de/svn/svn 3 D VCSoftware/tags/HTM -7.0/

[0049] The latest reference software description as well as the working draft of 3D-

HEVC is to be available as follows:

Gerhard Tech, Krzysztof Wegner, Ying Chen, Sehoon Yea, "3D-HEVC Test Model 4," JCT3V-D1005_spec_vl, Joint Collaborative Team on 3D Video Coding Extension Development of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 4th Meeting: Incheon, KR , 20-26 Apr. 2013. The software can be downloaded from the following link:

http://phenix.it-siidpans.eu/ict2/doc end user/dociiments/4 Incheon/wg l 1/JCT3V-

[0050] To further improve the coding efficiency, two new technologies namely "interview motion prediction" and "inter-view residual prediction" have been adopted in the latest reference software. To enable these two coding tools, the first step is to derive a disparity vector. The disparity vector is used either to locate the corresponding block in the other view for inter- view motion/residual prediction, or the disparity vector may be converted to a disparity motion vector for inter- view motion prediction.

Section 2.4.1 Implicit disparity vector

[0051] An implicit disparity vector (IDV) is generated when a PU employs inter- view motion vector prediction, i.e., the candidate for AMVP or merge modes is derived from a corresponding block in the other view with the help of a disparity vector. Such a disparity vector is called IDV. The IDV is stored to the PU for the purpose of disparity vector derivation.

Section 2.4.2 Disparity vector derivation process

[0052] To derive a disparity vector, the method called Neighboring Block-based Disparity Vector (NBDV) is used in current 3D-HTM. NBDV utilizes disparity motion vectors from spatial and temporal neighboring blocks. In NBDV, the motion vectors of spatial or temporal neighboring blocks are checked in a fixed checking order. Once a disparity motion vector or an IDV is identified, the checking process is terminated and the identified disparity motion vector is returned and converted to the disparity vector which will be used in inter-view motion prediction and inter-view residue prediction. If no such disparity vector is found after checking all the pre-defined neighboring blocks, a zero disparity vector will be used for the inter-view motion prediction while inter-view residual prediction will be disabled for the corresponding prediction unit (PU).

[0053] The spatial and temporal neighboring blocks used for NBDV are introduced in the following part, followed by the checking order.

• Spatial Neighboring Blocks

[0054] Five spatial neighboring blocks are used for the disparity vector derivation.

They are: the below-left, left, above-right, above and above-left blocks of current prediction unit (PU), denoted by A₀, A_l5 B₀, Bi or B₂, as defined in FIG. 16.

• Temporal Neighboring Blocks

[0055] Up to two reference pictures from the current view, the co-located picture and the random-access picture or the reference picture with the smallest POC difference and smallest temporal ID are considered for temporal block checks. The random-access picture is first checked, followed by the co-located picture. For each candidate picture, two candidate blocks are checked: a) Center block (CR): The center 4x4 block of the co-located region of the current PU, see 'Pos. A' in FIG. 3. b) Bottom Right block (BR): Bottom-right 4x4 block of co-located region of the current PU, see 'Pos. B' in FIG. 3

• Checking order

[0056] Whether DMVs are used is firstly checked for all the spatial/temporal

neighboring blocks, followed by ID Vs. Spatial neighboring blocks are firstly checked, followed by temporal neighboring blocks.

• Five spatial neighboring blocks are checked in the order of Ai, Bi, Bo, Ao and B₂.

If one of them uses DMV, the checking process is terminated and the

corresponding DMV will be used as the final disparity vector. • For each candidate picture, the two blocks are checked in order, CR and BR for the first non-base view or BR, CR for the second non-base view. If one of them uses DMV, the checking process is terminated and the corresponding DMV will be used as the final disparity vector.

• Five spatial neighboring blocks are checked in the order of Ao, A_l5 Bo, Bi and B₂ (see FIG. 16). If one of them uses IDV and it is coded as skip/merge mode, the checking process is terminated and the corresponding IDV will be used as the final disparity vector.

Section 2.4.3 Refining the disparity vector

[0057] The disparity vector, generated from the NBDV scheme could be further refined using the information in the coded depth map. That is, the accuracy of the disparity vector may be enhanced by taking benefit of the information coded base view depth map. Some example refinement steps are described as follows:

1. Locate a corresponding depth block by the derived disparity vector in the previously coded reference depth view, such as the base view; the size of the corresponding depth block is the same as that of current PU.

2. A disparity vector is calculated from the collocated depth block, from the maximum value of the four corner depth values. This is set equal to the horizontal component of a disparity vector, while the vertical component of the disparity vector is set to 0.

[0058] This new disparity vector is called as "depth oriented neighboring block based disparity vector (DoNBDV)." The disparity vector from NBDV scheme is then replaced by this newly derived disparity vector from the DoNBDV scheme for interview candidate derivation for the AMVP and merge modes. Note that the unrefined disparity vector is used for inter-view residual prediction. In addition, the refined disparity vector is stored as the motion vector of one PU if it is coded with backward VSP mode. Section 2.4.4 Block-based view synthesis prediction using neighboring blocks in 3D-HEVC

[0059] The backward- warping VSP approach as proposed in document JCT3V-C0152 was adopted in the 3rd JCT-3V meeting. The basic idea of this backward- warping VSP is the same as the block-based VSP in 3D-AVC. Both of these two techniques use the backward- warping and block-based VSP to avoid transmitting the motion vector differences and use more precise motion vectors. Implementation details are different due to different platforms.

[0060] In the following paragraphs, this disclosure also uses the term "BVSP" to indicate the backward- warping VSP approach in 3D-HEVC.

[0061] In 3D-HTM, texture first coding is applied in common test conditions. The corresponding non-base depth view is unavailable when decoding one non-base texture view. Therefore, the depth information is estimated and used to perform BVSP.

[0062] In order to estimate the depth information for a block, it is proposed to first derive a disparity vector from the neighboring blocks, and then use the derived disparity vector to obtain a depth block from a reference view.

[0063] In HTM 5.1 test model, there exists a process to derive a disparity vector predictor, known as NBDV (Neighboring Block Disparity Vector). Let (dv_x, dv_y) denote the disparity vector identified from NBDV function, and the current block position is (block_x, block_y). It is proposed to fetch a depth block at (block_x+dv_x, block_y+dv_y) in the depth image of the reference view. The fetched depth block would have the same size of the current prediction unit (PU), and it will then be used to do backward warping for the current PU. FIG. 4 shows the three steps how a depth block from the reference view is located and then used for BVSP prediction. In this way, FIG. 4 shows depth block derivation from a reference view to do BVSP prediction.

Changes to NBDV

[0064] If BVSP is enabled in the sequence, the NBDV process for inter-view motion prediction is changed and the differences are highlighted in the following paragraphs: For each of the temporal neighboring blocks, if it uses a disparity motion vector, the disparity motion vector is returned as the disparity vector and it is further refined with the method described in Section 2.4.3 above.

For each of the spatial neighboring blocks, the following apply:

For each reference picture list 0 or reference picture list 1. the following apply

■ II it uses a disparity motion vector, the disparity motion vector is returned as the disparity vector and it is further refined with the method described in Section 2.4.3 above.

Otherwise, if it uses BVSP mode, the associated motion vector returned as the the disparity vector. It is further refined in a similar way as described in Section 2.4.3 above. However, the maximum depth value is selected from all pixels of the

corresponding depth block rather than four corner pixels.

For each of the spatial neighboring blocks, if it uses an IDV, the IDV is returned as the disparity vector and it is further refined with the method described in Section 2.4.3 above.

Indication of BVSP coded PUs

[0065] The introduced BVSP mode is treated as a special inter-coded mode and a flag indicating the usage of BVSP mode should be maintained for each PU. Rather than signalling the flag in the bit stream, a new merging candidate (BVSP merging candidate) is added to the merge candidate list and the flag is dependent on whether the decoded merge candidate index corresponds to a BVSP merging candidate. The BVSP merging candidate is defined as follows:

• Reference picture index for each reference picture list: -1

• Motion vector for each reference picture list: the refined disparity vector

[0066] The inserted position of BVSP merging candidate is dependent on the spatial neighbouring blocks:

- If any of the five spatial neighbouring blocks (AO, Al, B0, Bl or B2) is coded with the BVSP mode, i.e., the maintained flag of the neighbouring block is equal to 1, BVSP merging candidate is treated as the corresponding spatial merging candidate and inserted to the merge candidate list. Note BVSP merging candidate will only be inserted to the merge candidate list once.

- Otherwise (none of the five spatial neighbouring blocks are coded with the

BVSP mode), the BVSP merging candidate is inserted to the merge candidate list just before the temporal merging candidates.

[0067] It is noted that during the combined bi-predictive merging candidate derivation process, additional conditions should be checked to avoid including the BVSP merging candidate.

Prediction derivation process

[0068] For each BVSP coded PU with its size denoted by NxM, it is further partitioned into several sub-regions with the size equal to KxK (wherein K may be 4 or 2). For each sub-region, a separate disparity motion vector is derived and each sub-region is predicted from one block located by the derived disparity motion vector in the interview reference picture. In other words, the size of motion-compensation unit for BVSP coded PUs are set to KxK. In common test conditions, K is set to 4.

Disparity motion vector derivation process

[0069] For each sub-region (4x4 block) within one PU coded with BVSP mode, a corresponding 4x4 depth block is firstly located in the reference depth view with the refined disparity vector aforementioned above. Secondly, the maximum value of the sixteen depth pixels in the corresponding depth block is selected. Thirdly, the maximum value is converted to the horizontal component of a disparity motion vector. The vertical component of the disparity motion vector is set to 0.

Section 2.4.5 Inter-view candidate derivation process for skip/merge mode

[0070] Based on the disparity vector derived from DoNBDV scheme, a new motion vector candidate, Inter- view Predicted Motion Vector Candidate (IPMVC), if available, may be added to AMVP and skip/merge modes. The inter- view predicted motion vector, if available, is a temporal motion vector.

[0071] Since skip mode has the same motion vector derivation process as merge mode, all techniques described in this document apply to both merge and skip modes. Some of the techniques described herein may also be used with motion information prediction according to the AM VP mode.

[0072] For the merge/skip mode, the inter-view predicted motion vector is derived by the following steps:

- A corresponding block of current PU/CU in a reference view of the same access unit is located by the disparity vector.

- If the corresponding block is not intra-coded and not inter-view predicted and its reference picture has a POC value equal to that of one entry in the same reference picture list of current PU/CU, its motion information (prediction direction, reference pictures, and motion vectors), after converting the reference index based on POC, is derived to be the inter- view predicted motion vector.

[0073] FIG. 5 shows an example of the derivation process of the inter-view predicted motion vector candidate.

[0074] In addition, the disparity vector is converted to an inter-view disparity motion vector, which is added into merge candidate list in a different position from IPMVC, or added into the AMVP candidate list in the same position as IPMVC when it is available. Either IPMVC or Inter- view Disparity Motion Vector Candidate (IDMVC) is called 'inter-view candidate' in this context.

[0075] In the merge/skip mode, IPMVC, if available, is always inserted before all spatial and temporal merging candidates to the merge candidate list. IDMVC is inserted before the spatial merging candidate derived from Ao.

Section 2.4.6 Merge candidate list construction for texture coding in 3D-HEVC

[0076] A disparity vector is firstly derived with the method of DoNBDV. With the disparity vector, the merging candidate list construction process in 3D-HEVC can be defined as follows:

1. IPMVC insertion

IPMVC is derived by the procedure described above. If it is available, it is inserted to the merge list.

2. Derivation process for spatial merging candidates and IDMVC insertion in

3D-HEVC Check the motion information of spatial neighbouring PUs in the following order: A_l5 B_l5 Bo, Ao, or B₂. Constrained pruning is performed by the following procedures:

- If Ai and IPMVC have the same motion vectors and the same reference indices, Ai is not inserted into the candidate list; otherwise it is inserted into the list.

- If Bi and Ai/IPMVC have the same motion vectors and the same

reference indices, Bi is not inserted into the candidate list; otherwise it is inserted into the list.

- If Bo is available, it is added to the candidate list. IDMVC is derived by the procedure described above. If it is available and it is different from the candidates derived from Ai and Bi, it is inserted to the candidate list.

- If BVSP is enabled for the whole picture or for the current slice, then the BVSP merging candidate is inserted to the merge candidate list.

- If A₀ is available, it is added to the candidate list.

- If B₂ is available, it is added to the candidate list.

ivation process for temporal merging candidate

Similar to the temporal merging candidate derivation process in HEVC where the motion information of the co-located PU is utilized, however, the target reference picture index of the temporal merging candidate may be changed instead of fixing to be 0. When the target reference index equal to 0 corresponds to a temporal reference picture (in the same view) while the motion vector of the co-located prediction unit (PU) points to an inter- view reference picture, it is changed to another index which corresponds to the first entry of inter- view reference picture in the reference picture list. On the contrary, when the target reference index equal to 0 corresponds to an interview reference picture while the motion vector of the co-located prediction unit (PU) points to a temporal reference picture, it is changed to another index which corresponds to the first entry of temporal reference picture in the reference picture list.

ivation process for combined bi-predictive merging candidates in 3D-

HEVC If the total number of candidates derived from the above two steps are less than the maximum number of candidates, the same process as defined in HEVC is performed except the specification of lOCandldx and HCandldx. The relationship among combldx, lOCandldx and HCandldx are defined in the table shown in FIG. 6, which is a table showing the specification of lOCandldx and HCandldx in 3D-HEVC

5. Derivation process for zero motion vector merging candidates

- The same procedure as defined in HEVC is performed.

[0077] In the latest software specification for 3D-HEVC, the total number of candidates in the MRG list is up to 6 and five_minus_max_num_merge_cand is signaled to specify the maximum number of the MRG candidates subtracted from 6 in slice header. It should be noticed that five_minus_max_num_merge_cand is in the range of 0 to 5, inclusive. Other total number of candidates could also be used, however, consistent with this disclosure.

Section 2.4.7 Motion Vector Inheritance for depth coding

[0078] The main idea behind the motion vector inheritance (MVI) is to exploit the similarity of the motion characteristics between the texture images and its associated depth images.

[0079] For a given PU in the depth image, the MVI candidate reuses using the motion vectors and reference indices of the already coded co-located texture region (with the same size as current depth block), if it is available. FIG. 7 shows an example of the derivation process of the MVI candidate for depth coding, where the corresponding center texture block is selected as the 4x4 block within the co-located texture region located to the bottom-right of the center of the current PU.

[0080] It should be noted that motion vectors with integer precision are used in depth coding while quarter precision of motion vectors is utilized for texture coding.

Therefore, the motion vector of the corresponding center texture block may be scaled before being used as a MVI candidate.

[0081] With the MVI candidate generation, the merge candidate list for the depth views is constructed as follows: I insertion

MVI is derived by the procedure described above. If it is available, it is inserted to the merge list.

ivation process for spatial merging candidates and IDMVC insertion in

3D-HEVC

Check the motion information of spatial neighboring PUs in the following order: A_{l 5} B_{l 5} B₀, A₀, or B₂. Constrained pruning is performed by the following procedures:

- If Ai and MVI have the same motion vectors and the same reference indices, Ai is not inserted into the candidate list.

- If Bi and Ai/MVIhave the same motion vectors and the same reference indices, Bi is not inserted into the candidate list.

- If Bo is available, it is added to the candidate list.

- If Ao is available, it is added to the candidate list.

- If B₂ is available, it is added to the candidate list.

ivation process for temporal merging candidate

Similar to the temporal merging candidate derivation process in HEVC where the motion information of the co-located PU is utilized, however, the target reference picture index of the temporal merging candidate may be changed as explained in Section 2.4.6 (set forth above) instead of fixing to be O.

ivation process for combined bi-predictive merging candidates in 3D-

HEVC

If the total number of candidates derived from the above two steps are less than the maximum number of candidates, the same process as defined in HEVC is performed except the specification of lOCandldx and HCandldx. The relationship among combldx, lOCandldx and HCandldx are defined in the Table of FIG. 6.

ivation process for zero motion vector merging candidates

- The same procedure as defined in HEVC is performed. Section 2.4.8 Inter-view residual prediction

[0082] In some proposals for 3D-HEVC, to more efficiently utilize the correlation between the residual signal of two views, inter- view residual prediction was realized by the so-called Advanced Residual Prediction (ARP), wherein the residual of the reference block identified with disparity vector was generated on-the-fly, as depicted in FIG. 8, instead of maintaining a residual picture for the reference view and directly predicting the residual within the reference block in the residual picture.

[0083] As shown in FIG. 8, to better predict the residual of the current block in a non- base view, denoted as Dc, the reference block Be is firstly identified by the disparity vector and the motion compensation of the reference block is invoked to derive the residual between the prediction signal Br and the reconstructed signal of the reference block Be. When the ARP mode is invoked, the predicted residual is added on top of the prediction signal of the non-base view, generated by e.g., motion compensation from the block Dr in the reference picture of the non-base view. One of the advantages of the ARP mode is that the motion vector used by the reference block (when generating the residue for ARP), is aligned with the motion vector of the current block, so the residual signal of the current block can be more precisely predicted. Therefore, the energy of the residue can be significantly reduced.

[0084] Since quantization difference between base (reference) and non-base views may lead to less prediction accuracy, two weighting factors are adaptively applied to the residue generated from the reference view: 0.5 and 1.

[0085] Since additional motion compensation at the base (reference) view may require significant increase of memory access and calculations, several ways to make the design more practical with minor sacrifice of coding efficiency have been adopted. Firstly, ARP mode is only enabled when the Prediction Unit (PU) is coded with 2Nx2N to reduce the computations especially at the encoder. Secondly, bi-linear filters are adopted for the motion compensation of both the reference block and the current block to significantly reduce the memory access for blocks coded with the ARP mode.

Thirdly, to improve the cache efficiency, although motion vectors may point to different pictures in the non-base view, the reference picture in the base view is fixed. In this case, the motion vector of the current block may need to be scaled based on the picture distances. Section 3 Problems

[0086] The current design of motion related technologies for the depth coding in HEVC based 3DV coders has the following problems:

• If the corresponding texture block from an already coded texture picture

associated with the current depth picture is in intra mode, the motion vector inheritance (MVI) candidate is considered as not available, in other words, not viable. In this case, the motion prediction from texture view to depth view is not enabled.

• The MVI candidate is only derived from the center block of the coded co-located texture region. If this block cannot provide an accurate motion vector, the MVI candidate will hardly bring good coding performance improvement.

Section 4 Solutions and additional details of techniques of this disclosure

[0087] This disclosure proposes techniques to improve the motion vector prediction for the depth views by deriving more candidates from the already coded pictures of the corresponding texture views. The techniques explained in this section may be performed by a depth processing unit of an encoder or a decoder, such as depth coding unit 125 of FIG. 11 or depth processing unit 165 of FIG. 12.

[0088] Multiple blocks (e.g., two more blocks) in corresponding texture picture are used to derive multiple MVI candidates. The involved blocks are the corresponding center texture block, the bottom-right neighboring 4x4 block of the block co-located with the current depth PU and the block shifting from the corresponding center texture block.

[0089] Various techniques of this disclosure may be further summarized as follows: 1. Multiple candidates are derived from corresponding texture PU. For each block, the motion information is utilized to create a merge candidate list similar to the current

MVI design.

1) A first candidate is the corresponding center texture block as in the current 3D- HEVC.

2) A second candidate is derived from the block which is in the bottom-right of the co-located texture region with the same size of current depth block. FIG. 9 shows an example of the derivation process of this new candidate where the corresponding texture block is selected as the 4x4 block located to the right bottom of the co-located texture region.

Alternatively, other 4x4 blocks within the co-located texture region may be used as the corresponding center texture block to derive the MVI candidates.

Alternatively, other 4x4 blocks surrounding the co-located texture region may be used as the corresponding center texture block to derive the MVI candidates.

3) A third candidate is derived from the block in corresponding texture picture by shifting the top-left sample both horizontally and vertically M (with M equal to 32, 16 or 8 pixels) and using it as a top-left sample to derive a 4x4 block.

Denote (x, y) be the top left corner of a corresponding texture block. The target block with the top left corner (x+M, y+M) is used to derive the block.

- In one alternative solution, the horizontal shifted value and vertical shifted value may be different.

- In one alternative solution, the horizontal shifted value and/or vertical

shifted value may be dependent on the PU size of current depth block.

- In one alterative solution, the block is shifted from the center block,

corresponding center texture block.

- In one alternative solution, the horizontal shifted value or the vertical

shifted value can be zero.

Insertion of the above candidates is based on different conditions. When the current MVI candidate is not available, the second candidate derived from bottom-right corresponding texture block (BR candidate) is inserted in the place where the current MVI candidate is introduced (e.g., the first position of merge candidate list, i.e., before all spatial merging candidates as in 3D-HEVC). In addition, the third candidate is added in the candidate list with the position before or after any of the temporal merging candidate, or the A_l5 B_l5 A₀, B₀ or B₂ merging candidate (see FIG. 16).

1) In one alternative, when the first candidate is not available, the third candidate is added in the candidate list. However, the second candidate is added in the candidate list regardless the availability of the first candidate. 2) In another alternative, more merge candidates derived from shifting may be added in to the merge candidate list.

- In addition, when two candidates derived from shifting are added in the candidate list, one is right before and one is right after an existing candidate, which may be any of the temporal merging candidate, or the Ai, Bi, Ao, Bo or B₂ candidate shown in FIG. 16.

3) In another alternative, the newly introduced two candidates are inserted to the merge candidate list next to each other.

4) In another alternative, the newly introduced two candidates are inserted to the merge candidate list regardless the availability of the first candidate.

5) In another alternative, the second and/or third candidate is added to the merge candidate list when a spatial or temporal merging candidate is not available.

3. Constrained pruning may be applied for each of the additional merge candidates.

1) In one example, the second or third candidate which is added to the merge

candidate list as a replacement of the first MVI candidate (when it is not available) does not need any pruning. In such an example, the third or second candidate may need pruning with the second or third candidate that replaced the first candidate.

2) When multiple shifted candidates are inserted, they may need to be pruned

together with the second candidate.

[0090] Again, the techniques set forth herein, and specifically those listed in the various points above, may be performed by a depth processing unit of an encoder or a decoder, such as depth coding unit 125 of FIG. 11 or depth processing unit 165 of FIG. 12. The phrases "merge candidate" and "merging candidate" are used above synonymously, and the phrases "merge list" and "merging list" are also used above synonymously.

Section 5 Some example implementation details

[0091] In this section, the implementation of one exemplary method is described for generating the additional candidates for the merge candidate list. The techniques explained in this section may be performed by a depth processing unit of an encoder or a decoder, such as depth coding unit 125 of FIG. 11 or depth processing unit 165 of FIG. 12. Section 5.1 Example #1

[0092] Two more candidates are derived from the corresponding texture picture of current depth picture. Firstly, two more blocks are identified. For a given block, the motion information is utilized to create a merge candidate list similar to the current MVI design.

1. BR candidate: This candidate is derived from the bottom-right 4x4 block of the texture co-located with the depth PU.

2. Shifted candidate: This candidate is derived from a 4x4 texture block located by shifting 32 pixels in both horizontal and vertical component from the top-left position of the texture block co-located with the depth PU.

Section 5.1.1 Merge candidate list construction for depth views with additional candidates

[0093] The two additional candidates are inserted in the merge candidate list that is highlighted.

1. MVI insertion

Current MVI is derived by the procedure described above. If it is not available, set the MVI candidate to BR candidate, if the BR candidate is available, If it the VI is available, it is inserted to the merge list.

2. Derivation process for spatial merging candidates and IDMVC insertion in

3D-HEVC

Check the motion information of spatial neighboring PUs in the following order: Ai, Bi, Bo, Ao, or B₂ relative to a current block. FIG. 16 illustrates the locations of Ai, Bi, Bo, Ao, or B₂ relative to a current block 161. Constrained pruning is performed by the following procedures:

- If B₀ is available, it is added to the candidate list.

- If A₀ is available, it is added to the candidate list. - If B₂ is available, it is added to the candidate list.

3. If the shifted candidate is available, the following apply:

- If the VI candidate (in step 1 ) is available, and the MVI candidate and shifted candidate have the same motion vectors and the same reference indices, the shifted candidate is not Inserted into the candidate list.

- Otherwise, the shifted candidate is added to the candidate list.

4. Derivation process for temporal merging candidate

5. Derivation process for combined bi-predictive merging candidates in 3D-

HEVC

6. Derivation process for zero motion vector merging candidates

- The same procedure as defined in HEVC is performed.

[0094] Consistent with the various solutions and examples explained above, a video coder (e.g., a video encoder or a video decoder) may perform methods for encoding 3D video data and methods for decoding 3D video data. The techniques may be applicable to a so-called "merge mode" or a so-called "skip mode," although the techniques may also be applicable to other modes that code data based on candidate lists. For example, advanced motion vector prediction (AMVP) modes may also use one or more techniques of this disclosure in creating a list of candidates for coding according to AMVP.

[0095] In one example of this disclosure, a method of coding depth data associated with 3D video data includes generating a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block, and coding the depth block based on the list. On the encoder side, the method may further include selecting one of the candidates to encode the depth block, and generating a syntax element that defines the selection. On the decoder side, the method may further include receiving a syntax element that defines a selection from the list, and decoding the depth block based on the selection from the list.

[0096] In one example, generating the list of candidates includes determining that a texture candidate that is co-located with the depth block is not a viable candidate, and replacing the texture candidate that is co-located with the depth block with the at least one texture candidate that is not co-located with the depth block. A candidate may not be a viable candidate for various reasons, such as when it is coded in an intra mode, when it has a motion vector equal to zero, or any other reason where the video encoder and the video decoder can be programmed to know that the candidate cannot provide an accurate motion vector for coding the depth block.

[0097] In some examples, the list may also include a texture candidate that is co-located with the depth block. In other words, in some cases the list may include both a texture candidate that is co-located with the depth block and one or more other texture candidates that are not co-located with the depth block, while in other cases, the list may include one or more other texture candidates that are not co-located with the depth block only when the texture candidate that is co-located with the depth block is excluded from the list.

[0098] As one example, the at least one texture candidate that is not co-located with the depth block may be a bottom right candidate relative to a texture candidate that is co- located with the depth block. A variety of other candidates, with other positions relative to a texture candidate that is co-located with the depth block, may also be used.

[0099] In another example, the at least one texture candidate that is not co-located with the depth block may comprise a shifted candidate that is shifted horizontally, vertically or both horizontally and vertically, relative to a texture candidate that is co-located with the depth block. For example, the shifted texture candidate may be shifted horizontally and vertically by M pixels, wherein M is an integer. M may be equal to 32, 16, 8 or another integer value, which is usually an even value and usually a value that is divisible by 4, although the techniques are not necessarily limited in this respect. Alternatively, the shifted texture candidate may be shifted horizontally by M pixels and vertically by N pixels, wherein M and N are different integers.

[0100] In many examples, the at least one texture candidate that is not co-located with the depth block comprises a plurality of texture candidates that are not co-located with the depth block. One of the plurality of texture candidates that are not co-located with the depth block may be a first ordered candidate in the list (i.e., the first one in the list). In some cases, another of the texture candidates that are not co-located with the depth block may be ordered second in the list, or possibly later in the list and e.g., after at least one or more spatial candidates in the list.

[0101] The method may further comprise pruning the list such that when two or more texture candidate that are not co-located with the depth block have a same motion vector, at least one of the two or more texture candidate that are not co-located with the depth block is excluded from the list (e.g., removed from the list or simply not inserted into the list). This pruning may avoid the case where duplicate candidates provide the same information for coding the depth block in a merge mode or skip mode.

[0102] In some examples, the method may further comprise determining whether one or more spatial candidates are viable candidates, and if one or more of the spatial candidates are not viable, inserting into the list another texture candidate that is not co- located with the depth block. That is, when one or more spatial candidates are not viable candidates, such candidates may be replaced with one or more viable texture candidates that are not co-located with the depth block

[0103] Furthermore, in some examples generating the list of candidates includes determining that a texture candidate that is co-located with the depth block is not a viable candidate, determining whether a bottom right texture candidate is a viable candidate, and if the bottom right texture candidate is a viable candidate, replacing the texture candidate that is co-located with the depth block with the bottom right texture candidate. In this case, upon determining that the bottom right texture candidate is a viable candidate, the method may further include determining whether a shifted texture candidate is a viable candidate, and if the shifted texture candidate is a viable candidate, replacing the texture candidate that is co-located with the depth block with the shifted texture candidate. In other words, the bottom right candidate may be given higher priority over one or more shifted candidates. [0104] In other examples, one or more shifted candidates or other non-co-located texture candidates (right, bottom, top, left, top left, top right, or bottom left) could also be given higher priority over the bottom right candidate. Any of these non-co-located texture candidates could be used in various examples, although the specific technique that gives first priority to the co-located candidate (if viable), next priority to the bottom right texture candidate (if viable), followed by next priority to one or more shifted candidates (if viable) may result in desirable coding efficiency and relatively simply implementation.

[0105] FIG. 10 is a block diagram illustrating an example video coding system 10 that may utilize the techniques of this disclosure. As described herein, the term "video coder" refers generically to both video encoders and video decoders. In this disclosure, the terms "video coding" or "coding" may refer generically to video encoding or video decoding.

[0106] As shown in FIG. 10, video coding system 10 includes a source device 12 and a destination device 14. Source device 12 generates encoded video data. Accordingly, source device 12 may be referred to as a video encoding device or a video encoding apparatus. Destination device 14 may decode the encoded video data generated by source device 12. Accordingly, destination device 14 may be referred to as a video decoding device or a video decoding apparatus. Source device 12 and destination device 14 may be examples of video coding devices or video coding apparatuses.

[0107] Source device 12 and destination device 14 may comprise a wide range of devices, including desktop computers, mobile computing devices, notebook (e.g., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called

"smart" phones, televisions, cameras, display devices, digital media players, video gaming consoles, in-car computers, or the like.

[0108] Destination device 14 may receive encoded video data from source device 12 via a channel 16. Channel 16 may comprise one or more media or devices capable of moving the encoded video data from source device 12 to destination device 14. In one example, channel 16 may comprise one or more communication media that enable source device 12 to transmit encoded video data directly to destination device 14 in realtime. In this example, source device 12 may modulate the encoded video data according to a communication standard, such as a wireless communication protocol, and may transmit the modulated video data to destination device 14. The one or more communication media may include wireless and/or wired communication media, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The one or more communication media may form part of a packet-based network, such as a local area network, a wide-area network, or a global network (e.g., the Internet). Channel 16 may include various types of devices, such as routers, switches, base stations, or other equipment that facilitate communication from source device 12 to destination device 14.

[0109] In another example, channel 16 may include a storage medium that stores encoded video data generated by source device 12. In this example, destination device 14 may access the storage medium via disk access or card access. The storage medium may include a variety of locally-accessed data storage media such as Blu-ray discs, DVDs, CD-ROMs, flash memory, or other suitable digital storage media for storing encoded video data.

[0110] In a further example, channel 16 may include a file server or another

intermediate storage device that stores encoded video data generated by source device 12. In this example, destination device 14 may access encoded video data stored at the file server or other intermediate storage device via streaming or download. The file server may be a type of server capable of storing encoded video data and transmitting the encoded video data to destination device 14. Example file servers include web servers (e.g., for a website), file transfer protocol (FTP) servers, network attached storage (NAS) devices, and local disk drives.

[0111] Destination device 14 may access the encoded video data through a standard data connection, such as an Internet connection. Example types of data connections may include wireless channels (e.g., Wi-Fi connections), wired connections (e.g., DSL, cable modem, etc.), or combinations of both that are suitable for accessing encoded video data stored on a file server. The transmission of encoded video data from the file server may be a streaming transmission, a download transmission, or a combination of both.

[0112] The techniques of this disclosure are not limited to wireless applications or settings. The techniques may be applied to video coding in support of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, streaming video transmissions, e.g., via the Internet, encoding of video data for storage on a data storage medium, decoding of video data stored on a data storage medium, or other applications. In some examples, video coding system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.

[0113] In the example of FIG. 10, source device 12 includes a video source 18, a video encoder 20, and an output interface 22. In some examples, output interface 22 may include a modulator/demodulator (modem) and/or a transmitter. Video source 18 may include a video capture device, e.g., a video camera, a video archive containing previously-captured video data, a video feed interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources of video data.

[0114] Video encoder 20 may encode video data from video source 18. In some examples, source device 12 directly transmits the encoded video data to destination device 14 via output interface 22. In other examples, the encoded video data may also be stored onto a storage medium or a file server for later access by destination device 14 for decoding and/or playback.

[0115] In the example of FIG. 10, destination device 14 includes an input interface 28, a video decoder 30, and a display device 32. In some examples, input interface 28 includes a receiver and/or a modem. Input interface 28 may receive encoded video data over channel 16. Display device 32 may be integrated with or may be external to destination device 14. In general, display device 32 displays decoded video data.

Display device 32 may comprise a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0116] In some examples, video encoder 20 and video decoder 30 operate according to a video compression standard, such as ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) and Multiview Video Coding (MVC) extensions. In other examples, video encoder 20 and video decoder 30 may operate according to other video compression standards, including the High Efficiency Video Coding (HEVC) standard presently under development. A draft of the HEVC standard currently being developed, referred to as "HEVC Working Draft 9," is described in Bross et al., "High Efficiency Video Coding (HEVC) text specification draft 9," Joint Collaborative Team on Video Coding (JCT- VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 11th Meeting: Shanghai, China, October, 2012, which is downloadable from http://phenix.int- eyry.fr/jct/doc end user/documents/ 1 1 Shanghai/wg l 1 /JCTVC-K 1003-v8.zip. The techniques of this disclosure, however, are not limited to any particular coding standard or technique. Another recent draft of the HEVC standard, referred to as "HEVC Working Draft 10" or "WD10," is described in document JCTVC-L1003v34, Bross et al., "High efficiency video coding (HEVC) text specification draft 10 (for FDIS & Last Call)," Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 12th Meeting: Geneva, CH, 14-23 January, 2013, which, as of July 15, 2013, is downloadable from http://phenix.int- eyry.fr/jct/doc end user/documents/12 Geneva/wgl l/JCTVC-L1003-v34.zip. Yet another draft of the HEVC standard, is referred to herein as "WD10 revisions" described in Bross et al., "Editors' proposed corrections to HEVC version 1," Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 13^th Meeting, Incheon, KR, April 2013, which as of July 15, 2013, is available from http://phenix.int- evry.fr/ict/doc end user/documents/ 13 Incheon/wg l l/JCTVC-M0432-v3.zip.

[0117] FIG. 10 is merely an example and the techniques of this disclosure may apply to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between the video encoding device and the video decoding device. In other examples, data is retrieved from a local memory, streamed over a network, or the like. A video encoding device may encode and store data to memory, and/or a video decoding device may retrieve and decode data from memory. In many examples, the video encoding and decoding is performed by devices that do not communicate with one another, but simply encode data to memory and/or retrieve and decode data from memory.

[0118] Video encoder 20 and video decoder 30 each may be implemented as any of a variety of suitable circuitry, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, hardware, or any combinations thereof. If the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Any of the foregoing (including hardware, software, a combination of hardware and software, etc.) may be considered to be one or more processors. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device.

[0119] This disclosure may generally refer to video encoder 20 "signaling" certain information. The term "signaling" may generally refer to the communication of syntax elements and/or other data used to decode the compressed video data. Such

communication may occur in real- or near-real-time. Alternately, such communication may occur over a span of time, such as might occur when storing syntax elements to a computer-readable storage medium in an encoded bitstream at the time of encoding, which a video decoding device may then retrieve at any time after being stored to this medium. In some examples, from an encoder perspective, signaling may include generating an encoded bitstream, and from a decoder perspective, signaling may include receiving and parsing a coded bitstream.

[0120] As mentioned briefly above, video encoder 20 encodes video data. The video data may comprise one or more pictures. Each of the pictures is a still image forming part of a video. When video encoder 20 encodes the video data, video encoder 20 may generate a bitstream. The bitstream may include a sequence of bits that form a coded representation of the video data. The bitstream may include coded pictures and associated data. A coded picture is a coded representation of a picture. The associated data may include sequence parameter sets (SPSs), picture parameter sets (PPSs), video parameter sets (VPSs), adaptive parameter sets (APSs), slice headers, block headers, and other syntax structures.

[0121] A picture may include three sample arrays, denoted S_L, Sc_b and Sc_r- S_L is a two- dimensional array (i.e., a block) of luma samples. Luma samples may also be referred to herein as "Y" samples. So, is a two-dimensional array of Cb chrominance samples. Sc_r is a two-dimensional array of Cr chrominance samples. Chrominance samples may also be referred to herein as "chroma" samples. Cb chrominance samples may be referred to herein as "U samples." Cr chrominance samples may be referred to herein as "V samples."

[0122] In some examples, video encoder 20 may down-sample the chroma arrays of a picture (i.e., SQ, and Sc_r)- For example, video encoder 20 may use a YUV 4:2:0 video format, a YUV 4:2:2 video format, or a 4:4:4 video format. In the YUV 4:2:0 video format, video encoder 20 may down-sample the chroma arrays such that the chroma arrays are ½ the height and ½ the width of the luma array. In the YUV 4:2:2 video format, video encoder 20 may down-sample the chroma arrays such that the chroma arrays are ½ the width and the same height as the luma array. In the YUV 4:4:4 video format, video encoder 20 does not down-sample the chroma arrays.

[0123] To generate an encoded representation of a picture, video encoder 20 may generate a set of coding tree units (CTUs). Each of the CTUs may be a coding tree block of luma samples, two corresponding coding tree blocks of chroma samples, and syntax structures used to code the samples of the coding tree blocks. A coding tree block may be an NxN block of samples. A CTU may also be referred to as a "tree block" or a "largest coding unit" (LCU). The CTUs of HEVC may be broadly analogous to the macroblocks of other standards, such as H.264/AVC. However, a CTU is not necessarily limited to a particular size and may include one or more coding units (CUs).

[0124] As part of encoding a picture, video encoder 20 may generate encoded representations of each slice of the picture (i.e., coded slices). To generate a coded slice, video encoder 20 may encode a series of CTUs. This disclosure may refer to an encoded representation of a CTU as a coded CTU. In some examples, each of the slices includes an integer number of coded CTUs.

[0125] To generate a coded CTU, video encoder 20 may recursively perform quad-tree partitioning on the coding tree blocks of a CTU to divide the coding tree blocks into coding blocks, hence the name "coding tree units." A coding block is an NxN block of samples. A CU may be a coding block of luma samples and two corresponding coding blocks of chroma samples of a picture that has a luma sample array, a Cb sample array and a Cr sample array, and syntax structures used to code the samples of the coding blocks. Video encoder 20 may partition a coding block of a CU into one or more prediction blocks. A prediction block may be a rectangular (i.e., square or non-square) block of samples on which the same prediction is applied. A prediction unit (PU) of a CU may be a prediction block of luma samples, two corresponding prediction blocks of chroma samples of a picture, and syntax structures used to predict the prediction block samples. Video encoder 20 may generate predictive luma, Cb and Cr blocks for luma, Cb and Cr prediction blocks of each PU of the CU. [0126] Video encoder 20 may use intra prediction or inter prediction to generate the predictive blocks for a PU. If video encoder 20 uses intra prediction to generate the predictive blocks of a PU, video encoder 20 may generate the predictive blocks of the PU based on decoded samples of the picture associated with the PU.

[0127] If video encoder 20 uses inter prediction to generate the predictive blocks of a PU, video encoder 20 may generate the predictive blocks of the PU based on decoded samples of one or more pictures other than the picture associated with the PU. Video encoder 20 may use uni-prediction or bi-prediction to generate the predictive blocks of a PU. When video encoder 20 uses uni-prediction to generate the predictive blocks for a PU, the PU may have a single MV. When video encoder 20 uses uni-prediction to generate the predictive blocks for a PU, the PU may have two MVs.

[0128] After video encoder 20 generates predictive luma, Cb and Cr blocks for one or more PUs of a CU, video encoder 20 may generate a luma residual block for the CU. Each sample in the CU's luma residual block indicates a difference between a luma sample in one of the CU's predictive luma blocks and a corresponding sample in the CU's original luma coding block. In addition, video encoder 20 may generate a Cb residual block for the CU. Each sample in the CU's Cb residual block may indicate a difference between a Cb sample in one of the CU's predictive Cb blocks and a corresponding sample in the CU's original Cb coding block. Video encoder 20 may also generate a Cr residual block for the CU. Each sample in the CU's Cr residual block may indicate a difference between a Cr sample in one of the CU's predictive Cr blocks and a corresponding sample in the CU's original Cr coding block.

[0129] Furthermore, video encoder 20 may use quad-tree partitioning to decompose the luma, Cb and Cr residual blocks of a CU into one or more luma, Cb and Cr transform blocks. A transform block may be a rectangular block of samples on which the same transform is applied. A transform unit (TU) of a CU may be a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax structures used to transform the transform block samples. Thus, each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block. The luma transform block associated with the TU may be a sub-block of the CU's luma residual block. The Cb transform block may be a sub-block of the CU's Cb residual block. The Cr transform block may be a sub-block of the CU's Cr residual block. For 3D coding, depth values in depth blocks may likewise be represented as sample values, each indicating a level of depth associated with a given pixel location. The techniques of this disclosure are applicable to the coding of depth blocks, particularly in modes such as skip mode or merge mode where a list of candidates is generated for inheriting or using motion information of a selected candidate, in coding the depth block.

[0130] Video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU. A coefficient block may be a two-dimensional array of transform coefficients. A transform coefficient may be a scalar quantity. Video encoder 20 may apply one or more transforms to a Cb transform block of a TU to generate a Cb coefficient block for the TU. Video encoder 20 may apply one or more transforms to a Cr transform block of a TU to generate a Cr coefficient block for the TU.

[0131] After generating a coefficient block (e.g., a luma coefficient block, a Cb coefficient block or a Cr coefficient block), video encoder 20 may quantize the coefficient block. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression. After video encoder 20 quantizes a coefficient block, video encoder 20 may entropy encoding syntax elements indicating the quantized transform coefficients. For example, video encoder 20 may perform Context- Adaptive Binary Arithmetic Coding (CAB AC) on the syntax elements indicating the quantized transform coefficients. Video encoder 20 may output the entropy-encoded syntax elements in a bitstream.

[0132] Video decoder 30 may receive a bitstream generated by video encoder 20. In addition, video decoder 30 may parse the bitstream to decode syntax elements from the bitstream. Video decoder 30 may reconstruct the pictures of the video data based at least in part on the syntax elements decoded from the bitstream. The process to reconstruct the video data may be generally reciprocal to the process performed by video encoder 20. For instance, video decoder 30 may use MVs of PUs to determine predictive sample blocks for the PUs of a current CU. In addition, video decoder 30 may inverse quantize transform coefficient blocks associated with TUs of the current CU. Video decoder 30 may perform inverse transforms on the transform coefficient blocks to reconstruct transform blocks associated with the TUs of the current CU.

Video decoder 30 may reconstruct the coding blocks of the current CU by adding the samples of the predictive sample blocks for PUs of the current CU to corresponding samples of the transform blocks of the TUs of the current CU. By reconstructing the coding blocks for each CU of a picture, video decoder 30 may reconstruct the picture.

[0133] In some cases, video encoder 20 may signal the motion information of a PU using merge mode or a skip mode, or possibly an advanced MV prediction (AMVP) mode. The motion information of a PU may include motion vector(s) of the PU and reference index(s) of the PU. When video encoder 20 signals the motion information of a current PU using merge mode, video encoder 20 generates a merge candidate list. The merge candidate list includes a set of candidates. The candidates may indicate the motion information of PUs that spatially or temporally neighbor the current PU. Video encoder 20 may then select a candidate from the candidate list and may use the motion information indicated by the selected candidate as the motion information of the current PU. Furthermore, in merge mode, video encoder 20 may signal the position in the candidate list of the selected candidate. Video decoder 30 may generate the same candidate list and may determine, based on the indication of the position of the selected candidate, the selected candidate. Video decoder 30 may then use the motion information of the selected candidate to generate predictive samples for the current PU, and may generate a residual signal as the difference between the current PU and predictive samples of the predictive PU identified in the merge mode.

[0134] Skip mode is similar to merge mode in that video encoder 20 generates a candidate list and selects a candidate from the list of candidates. However, when video encoder 20 signals the motion information of a current PU (e.g. a depth block) using skip mode, video encoder 20 may avoid generation of any residual signal.

[0135] AMVP mode is similar to merge mode in that video encoder 20 generates a candidate list and selects a candidate from the list of candidates. However, when video encoder 20 signals the motion information of a current PU (e.g. a depth block) using AMVP mode, video encoder 20 may signal a motion vector difference (MVD) for the current PU and a reference index in addition to signaling a position of the selected candidate in the candidate list. An MVD for the current PU may indicate a difference between an MV of the current PU and an MV of the selected MV candidate. In uni- prediction, video encoder 20 may signal one MVD and one reference indexes for the current PU. In bi-prediction, video encoder 20 may signal two MVDs and two reference indexes for the current PU. For depth block prediction consistent with this disclosure, video encoder 20 would typically signal one MVD and one reference indexes for the current PU, although depth block prediction could also use techniques similar to bi-prediction where two MVDs and two reference indexes are signaled.

[0136] Furthermore, when the motion information of a current PU is signaled using AMVP mode, video decoder 30 may generate the same candidate list and may determine, based on the indication of the position of the selected candidate, the selected candidate. Video decoder 30 may recover an MV of the current PU by adding a MVD to the MV of the selected candidate. Video decoder 30 may then use the recovered MV or MVs of the current PU to generate predictive sample blocks for the current PU.

[0137] In accordance with this disclosure, video encoder 20 and video decoder 30 may perform one or more techniques described herein as part of a video coding process (e.g., video encoding or video decoding). The techniques of this disclosure may be applicable to the coding (encoding or decoding) of depth blocks, particularly in modes such as skip mode, merge mode, or AMVP mode where a list of candidates is generated for inheriting or using motion information of a selected candidate, in coding the depth block. The techniques of this disclosure may be particularly useful for merge mode or skip mode, although similar techniques might also be useful for AMVP mode.

[0138] FIG. 11 is a block diagram illustrating an example video encoder 20 that may implement the techniques of this disclosure. FIG. 11 is provided for purposes of explanation and should not be considered limiting of the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video encoder 20 in the context of HEVC coding. However, the techniques of this disclosure may be applicable to other coding standards or methods.

[0139] In the example of FIG. 11, video encoder 20 includes a prediction processing unit 100, a residual generation unit 102, a transform processing unit 104, a quantization unit 106, an inverse quantization unit 108, an inverse transform processing unit 110, a reconstruction unit 112, a filter unit 114, a decoded picture buffer 116, and an entropy encoding unit 118. Prediction processing unit 100 includes an inter-prediction processing unit 120 and an intra-prediction processing unit 126. Inter-prediction processing unit 120 includes a motion estimation unit 122 and a motion compensation unit 124. In other examples, video encoder 20 may include more, fewer, or different functional components.

[0140] Video encoder 20 may receive video data. Video encoder 20 may encode each CTU in a slice of a picture of the video data. Each of the CTUs may be associated with equally-sized luma coding tree blocks (CTBs) and corresponding CTBs of the picture. As part of encoding a CTU, prediction processing unit 100 may perform quad-tree partitioning to divide the CTBs of the CTU into progressively-smaller blocks. The smaller block may be coding blocks of CUs. For example, prediction processing unit 100 may partition a CTB associated with a CTU into four equally-sized sub-blocks, partition one or more of the sub-blocks into four equally-sized sub- sub-blocks, and so on.

[0141] Video encoder 20 may encode CUs of a CTU to generate encoded

representations of the CUs (i.e., coded CUs). As part of encoding a CU, prediction processing unit 100 may partition the coding blocks associated with the CU among one or more PUs of the CU. Thus, each PU may be associated with a luma prediction block and corresponding chroma prediction blocks. Video encoder 20 and video decoder 30 may support PUs having various sizes. As indicated above, the size of a CU may refer to the size of the luma coding block of the CU and the size of a PU may refer to the size of a luma prediction block of the PU. Assuming that the size of a particular CU is 2Nx2N, video encoder 20 and video decoder 30 may support PU sizes of 2Nx2N or NxN for intra prediction, and symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, NxN, or similar for inter prediction. Video encoder 20 and video decoder 30 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter prediction.

[0142] Inter-prediction processing unit 120 may generate predictive data for a PU by performing inter prediction on each PU of a CU. The predictive data for the PU may include a predictive sample blocks of the PU and motion information for the PU. Inter- prediction unit 121 may perform different operations for a PU of a CU depending on whether the PU is in an I slice, a P slice, or a B slice. In an I slice, all PUs are intra predicted. Hence, if the PU is in an I slice, inter-prediction unit 121 does not perform inter prediction on the PU. Thus, for blocks encoded in I-mode, the predicted block is formed using spatial prediction from previously-encoded neighboring blocks within the same frame.

[0143] If a PU is in a P slice, motion estimation unit 122 may search the reference pictures in a list of reference pictures (e.g., "RefPicListO") for a reference region for the PU. The reference region for the PU may be a region, within a reference picture, that contains sample blocks that most closely corresponds to the sample blocks of the PU. Motion estimation unit 122 may generate a reference index that indicates a position in RefPicListO of the reference picture containing the reference region for the PU. In addition, motion estimation unit 122 may generate an MV that indicates a spatial displacement between a coding block of the PU and a reference location associated with the reference region. For instance, the MV may be a two-dimensional vector that provides an offset from the coordinates in the current decoded picture to coordinates in a reference picture. Motion estimation unit 122 may output the reference index and the MV as the motion information of the PU. Motion compensation unit 124 may generate the predictive sample blocks of the PU based on actual or interpolated samples at the reference location indicated by the motion vector of the PU.

[0144] If a PU is in a B slice, motion estimation unit 122 may perform uni-prediction or bi-prediction for the PU. To perform uni-prediction for the PU, motion estimation unit 122 may search the reference pictures of RefPicListO or a second reference picture list ("RefPicListl") for a reference region for the PU. Motion estimation unit 122 may output, as the motion information of the PU, a reference index that indicates a position in RefPicListO or RefPicListl of the reference picture that contains the reference region, an MV that indicates a spatial displacement between a sample block of the PU and a reference location associated with the reference region, and one or more prediction direction indicators that indicate whether the reference picture is in RefPicListO or RefPicListl. Motion compensation unit 124 may generate the predictive sample blocks of the PU based at least in part on actual or interpolated samples at the reference region indicated by the motion vector of the PU.

[0145] To perform bi-directional inter prediction for a PU, motion estimation unit 122 may search the reference pictures in RefPicListO for a reference region for the PU and may also search the reference pictures in RefPicListl for another reference region for the PU. Motion estimation unit 122 may generate reference picture indexes that indicate positions in RefPicListO and RefPicListl of the reference pictures that contain the reference regions. In addition, motion estimation unit 122 may generate MVs that indicate spatial displacements between the reference location associated with the reference regions and a sample block of the PU. The motion information of the PU may include the reference indexes and the MVs of the PU. Motion compensation unit 124 may generate the predictive sample blocks of the PU based at least in part on actual or interpolated samples at the reference region indicated by the motion vector of the PU. [0146] In accordance with one or more techniques of this disclosure, one or more units within video encoder 20 may perform one or more techniques described herein as part of a video encoding process. Additional 3D components may also be included within video encoder 20, such as for example, depth processing unit 125. Depth processing unit 125 may perform techniques to code depth views, and may execute a merge mode or a skip mode to do so. When coding the depth view, depth processing unit 125 may implement techniques of this disclosure, which may include the generation of a list of candidates used for coding the depth view. Moreover, the list may be extended to include texture candidates that are not actually co-located with or corresponding to the depth view.

[0147] In one example, depth processing unit 125 may execute a method of encoding depth data associated with 3D video data. Depth processing unit 125 may generate a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co- located with the depth block, and coding the depth block based on the list. Depth processing unit 125 may select one of the candidates to encode the depth block, and generate a syntax element that defines the selection, which may be included within an encoded bitstream.

[0148] In one example, depth processing unit 125 generates the list of candidates via a process that includes determining that a texture candidate that is co-located with the depth block is not a viable candidate, and replacing the texture candidate that is co- located with the depth block with the at least one texture candidate that is not co-located with the depth block. Again, a candidate may not be a viable candidate for various reasons, such as when it is coded in an intra mode, when it has a motion vector equal to zero, or any other reason where the video encoder and the video decoder can be programmed to know that the candidate cannot provide an accurate motion vector for coding the depth block.

[0149] In some examples, the list generated by depth processing unit 125 may also include a texture candidate that is co-located with the depth block. In other words, in some cases the list may include both a texture candidate that is co-located with the depth block and one or more other texture candidates that are not co-located with the depth block, while in other cases, the list may include one or more other texture candidates that are not co-located with the depth block only when the texture candidate that is co- located with the depth block is excluded from the list.

[0150] As one example, the at least one texture candidate that is not co-located with the depth block may be a bottom right candidate relative to a texture candidate that is co- located with the depth block. A variety of other candidates, with other positions relative to a texture candidate that is co-located with the depth block, may also be used by depth processing unit 125.

[0151] In another example, the at least one texture candidate that is not co-located with the depth block may comprise a shifted candidate that is shifted horizontally, vertically or both horizontally and vertically, relative to a texture candidate that is co-located with the depth block. For example, the shifted texture candidate may be shifted horizontally and vertically by M pixels, wherein M is an integer. M may be equal to 32, 16, 8 or another integer value, usually an even value and usually a value that is divisible by 4, although the techniques are not necessarily limited in this respect. Alternatively, the shifted texture candidate may be shifted horizontally by M pixels and vertically by N pixels, wherein M and N are different integers.

[0152] In many examples, the at least one texture candidate that is not co-located with the depth block comprises a plurality of texture candidates that are not co-located with the depth block. One of the plurality of texture candidates that are not co-located with the depth block may be a first ordered candidate in the list (i.e., the first one in the list). In some cases, another of the texture candidates that are not co-located with the depth block may be ordered second in the list, or possibly later in the list and e.g., after at least one spatial candidate in the list.

[0153] Depth processing unit 125 may also pruning the list such that when two or more texture candidate that are not co-located with the depth block have a same motion vector, at least one of the two or more texture candidate that are not co-located with the depth block is excluded from the list. This pruning may avoid the case where duplicate candidates provide the same information for coding the depth block in a merge mode or skip mode (or possibly another mode that uses lists of candidates, such as AMVP mode).

[0154] In some examples, depth processing unit 125 may determine whether one or more spatial candidates are viable candidates, and if one or more of the spatial candidates are not viable, insert into the list another texture candidate that is not co- located with the depth block. [0155] Furthermore, in some examples depth processing unit 125 may generate the list of candidates via a process that includes determining that a texture candidate that is co- located with the depth block is not a viable candidate, determining whether a bottom right texture candidate is a viable candidate, and if the bottom right texture candidate is a viable candidate, replacing the texture candidate that is co-located with the depth block with the bottom right texture candidate. In this case, upon determining that the bottom right texture candidate is a viable candidate, depth processing unit 125 may further determine whether a shifted texture candidate is a viable candidate, and if the shifted texture candidate is a viable candidate, replacing the texture candidate that is co- located with the depth block with the shifted texture candidate. In other words, the bottom right candidate may be given higher priority over one or more shifted candidates. As mentioned above, in other examples, one or more shifted candidates or other non-co- located texture candidates (right, bottom, top, left, top left, top right, or bottom left) could also be given higher priority over the bottom right candidate. Any of these non- co-located texture candidates could be used in various examples, although the specific technique that gives first priority to the co-located candidate (if viable), next priority to the bottom right texture candidate (if viable), followed by next priority to one or more shifted candidates (if viable) may result in desirable coding efficiency and relatively simple implementation.

[0156] Continued reference is now made to the example of FIG. 11. Intra-prediction processing unit 126 may generate predictive data for a PU by performing intra prediction on the PU. The predictive data for the PU may include predictive sample blocks for the PU and various syntax elements. Intra-prediction processing unit 126 may perform intra prediction on PUs in I slices, P slices, and B slices.

[0157] To perform intra prediction on a PU, intra-prediction processing unit 126 may use multiple intra prediction modes to generate multiple sets of predictive data for the PU. To use an intra prediction mode to generate a set of predictive data for the PU, intra-prediction processing unit 126 may extend samples from sample blocks of neighboring PUs across the sample blocks of the PU in a direction associated with the intra prediction mode. The neighboring PUs may be above, above and to the right, above and to the left, or to the left of the PU, assuming a left-to-right, top-to-bottom encoding order for PUs, CUs, and CTUs. Intra-prediction processing unit 126 may use various numbers of intra prediction modes, e.g., 33 directional intra prediction modes. In some examples, the number of intra prediction modes may depend on the size of the region associated with the PU.

[0158] Prediction processing unit 100 may select the predictive data for PUs of a CU from among the predictive data generated by inter-prediction processing unit 120 for the PUs or the predictive data generated by intra-prediction processing unit 126 for the PUs. In some examples, prediction processing unit 100 selects the predictive data for the PUs of the CU based on rate/distortion metrics of the sets of predictive data. The predictive sample blocks of the selected predictive data may be referred to herein as the selected predictive sample blocks.

[0159] Residual generation unit 102 may generate, based on the luma, Cb and Cr coding block of a CU and the selected predictive luma, Cb and Cr blocks of the PUs of the CU, a luma, Cb and Cr residual blocks of the CU. For instance, residual generation unit 102 may generate the residual blocks of the CU such that each sample in the residual blocks has a value equal to a difference between a sample in a coding block of the CU and a corresponding sample in a corresponding selected predictive sample block of a PU of the CU.

[0160] Transform processing unit 104 may perform quad- tree partitioning to partition the residual blocks associated with a CU into transform blocks associated with TUs of the CU. Thus, a TU may be associated with a luma transform block and two chroma transform blocks. The sizes and positions of the luma and chroma transform blocks of TUs of a CU may or may not be based on the sizes and positions of prediction blocks of the PUs of the CU. A quad-tree structure known as a "residual quad-tree" (RQT) may include nodes associated with each of the regions. The TUs of a CU may correspond to leaf nodes of the RQT.

[0161] Transform processing unit 104 may generate transform coefficient blocks for each TU of a CU by applying one or more transforms to the transform blocks of the TU. Transform processing unit 104 may apply various transforms to a transform block associated with a TU. For example, transform processing unit 104 may apply a discrete cosine transform (DCT), a directional transform, or a conceptually similar transform to a transform block. In some examples, transform processing unit 104 does not apply transforms to a transform block. In such examples, the transform block may be treated as a transform coefficient block. [0162] Quantization unit 106 may quantize the transform coefficients in a coefficient block. The quantization process may reduce the bit depth associated with some or all of the transform coefficients. For example, an ra-bit transform coefficient may be rounded down to an m-bit transform coefficient during quantization, where n is greater than m. Quantization unit 106 may quantize a coefficient block associated with a TU of a CU based on a quantization parameter (QP) value associated with the CU. Video encoder 20 may adjust the degree of quantization applied to the coefficient blocks associated with a CU by adjusting the QP value associated with the CU. Quantization may introduce loss of information, thus quantized transform coefficients may have lower precision than the original ones.

[0163] Inverse quantization unit 108 and inverse transform processing unit 110 may apply inverse quantization and inverse transforms to a coefficient block, respectively, to reconstruct a residual block from the coefficient block. Reconstruction unit 112 may add the reconstructed residual block to corresponding samples from one or more predictive sample blocks generated by prediction processing unit 100 to produce a reconstructed transform block associated with a TU. By reconstructing transform blocks for each TU of a CU in this way, video encoder 20 may reconstruct the coding blocks of the CU.

[0164] Filter unit 114 may perform one or more deblocking operations to reduce blocking artifacts in the coding blocks associated with a CU. Decoded picture buffer 116 may store the reconstructed coding blocks after filter unit 114 performs the one or more deblocking operations on the reconstructed coding blocks. Inter-prediction unit 120 may use a reference picture that contains the reconstructed coding blocks to perform inter prediction on PUs of other pictures. In addition, intra-prediction processing unit 126 may use reconstructed coding blocks in decoded picture buffer 116 to perform intra prediction on other PUs in the same picture as the CU.

[0165] Entropy encoding unit 118 may receive data from other functional components of video encoder 20. For example, entropy encoding unit 118 may receive coefficient blocks from quantization unit 106 and may receive syntax elements from prediction processing unit 100. Entropy encoding unit 118 may perform one or more entropy encoding operations on the data to generate entropy-encoded data. For example, entropy encoding unit 118 may perform a context-adaptive variable length coding (CAVLC) operation, a CAB AC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a Probability Interval Partitioning Entropy (PIPE) coding operation, an Exponential- Golomb encoding operation, or another type of entropy encoding operation on the data. Video encoder 20 may output a bitstream that includes entropy-encoded data generated by entropy encoding unit 118. For instance, the bitstream may include data that represents a RQT for a CU.

[0166] FIG. 12 is a block diagram illustrating an example video decoder 30 that is configured to implement the techniques of this disclosure. FIG. 12 is provided for purposes of explanation and is not limiting on the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video decoder 30 in the context of HEVC coding. However, the techniques of this disclosure may be applicable to other coding standards or methods.

[0167] In the example of FIG. 12, video decoder 30 includes an entropy decoding unit 150, a prediction processing unit 152, an inverse quantization unit 154, an inverse transform processing unit 156, a reconstruction unit 158, a filter unit 160, and a decoded picture buffer 162. Prediction processing unit 152 includes a motion compensation unit 164 and an intra-prediction processing unit 166. In other examples, video decoder 30 may include more, fewer, or different functional components.

[0168] Video decoder 30 may receive a bitstream. Entropy decoding unit 150 may parse the bitstream to decode syntax elements from the bitstream. Entropy decoding unit 150 may entropy decode entropy-encoded syntax elements in the bitstream.

Prediction processing unit 152, inverse quantization unit 154, inverse transform processing unit 156, reconstruction unit 158, and filter unit 160 may generate decoded video data based on the syntax elements extracted from the bitstream.

[0169] The bitstream may comprise a series of NAL units. The NAL units of the bitstream may include coded slice NAL units. As part of decoding the bitstream, entropy decoding unit 150 may extract and entropy decode syntax elements from the coded slice NAL units. Each of the coded slices may include a slice header and slice data. The slice header may contain syntax elements pertaining to a slice. The syntax elements in the slice header may include a syntax element that identifies a PPS associated with a picture that contains the slice.

[0170] In addition to decoding syntax elements from the bitstream, video decoder 30 may perform a reconstruction operation on a non-partitioned CU. To perform the reconstruction operation on a non-partitioned CU, video decoder 30 may perform a reconstruction operation on each TU of the CU. By performing the reconstruction operation for each TU of the CU, video decoder 30 may reconstruct residual blocks of the CU.

[0171] As part of performing a reconstruction operation on a TU of a CU, inverse quantization unit 154 may inverse quantize, i.e., de-quantize, coefficient blocks associated with the TU. Inverse quantization unit 154 may use a QP value associated with the CU of the TU to determine a degree of quantization and, likewise, a degree of inverse quantization for inverse quantization unit 154 to apply. That is, the compression ratio, i.e., the ratio of the number of bits used to represent original sequence and the compressed one, may be controlled by adjusting the value of the QP used when quantizing transform coefficients. The compression ratio may also depend on the method of entropy coding employed.

[0172] After inverse quantization unit 154 inverse quantizes a coefficient block, inverse transform processing unit 156 may apply one or more inverse transforms to the coefficient block in order to generate a residual block associated with the TU. For example, inverse transform processing unit 156 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the coefficient block.

[0173] If a PU is encoded using intra prediction, intra-prediction processing unit 166 may perform intra prediction to generate predictive blocks for the PU. Intra-prediction processing unit 166 may use an intra prediction mode to generate the predictive luma, Cb and Cr blocks for the PU based on the prediction blocks of spatially-neighboring PUs. Intra-prediction processing unit 166 may determine the intra prediction mode for the PU based on one or more syntax elements decoded from the bitstream.

[0174] Prediction processing unit 152 may construct a first reference picture list (RefPicListO) and a second reference picture list (RefPicListl) based on syntax elements extracted from the bitstream. Furthermore, if a PU is encoded using inter prediction, entropy decoding unit 150 may extract motion information for the PU. Motion compensation unit 164 may determine, based on the motion information of the PU, one or more reference regions for the PU. Motion compensation unit 164 may generate, based on samples blocks at the one or more reference blocks for the PU, predictive luma, Cb and Cr blocks for the PU.

[0175] As indicated above, video encoder 20 may signal the motion information of a PU using merge mode, skip mode or AMVP mode. When video encoder 20 signals the motion information of a current PU using AMVP mode, entropy decoding unit 150 may decode, from the bitstream, a reference index, a MVD for the current PU, and a candidate index. Furthermore, motion compensation unit 164 may generate an AMVP candidate list for the current PU. The AMVP candidate list includes one or more MV predictor candidates. Each of the MV predictor candidates specifies a MV of a PU that spatially or temporally neighbors the current PU. Motion compensation unit 164 may determine, based at least in part on the candidate index, a selected MV predictor candidate in the AMVP candidate list. Motion compensation unit 164 may then determine the MV of the current PU by adding the MVD to the MV specified by the selected MV predictor candidate. In other words, for AMVP, MV is calculated as MV = MVP + MVD, wherein the index of the motion vector predictor (MVP) is signaled and the MVP is one of the MV candidates (spatial or temporal) from the AMVP list, and the MVD is signaled to the decoder side.

[0176] If the current PU is bi-predicted, entropy decoding unit 150 may decode an additional reference index, MVD, and candidate index from the bitstream. Motion compensation unit 162 may repeat the process described above using the additional reference index, MD, and candidate index to derive a second MV for the current PU. In this way, motion compensation unit 162 may derive a MV for RefPicListO (i.e., a RefPicListO MV) and a MV for RefPicListl (i.e., a RefPicListl MV).

[0177] In accordance with one or more techniques of this disclosure, one or more units within video decoder 30 may perform one or more techniques described herein as part of a video decoding process. Additional 3D components may also be included within video decoder 30, such as for example, depth processing unit 165. Depth processing unit 165 may perform techniques to code depth views, and may execute a merge mode or a skip mode to do so. When coding the depth view, depth processing unit 165 may implement techniques of this disclosure, which may include the generation of a list of candidates used for coding the depth view. Moreover, the list may be extended to include texture candidates that are not actually co-located with or corresponding to the depth view. [0178] In one example, depth processing unit 165 may implement a method of decoding depth data associated with 3D video data. In doing so, depth processing unit 165 may generate a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block, and coding the depth block based on the list. Depth processing unit 165 may receive a syntax element that defines a selection from the list, and depth processing unit 165 decoding the depth block based on the selection from the list. The syntax element may be entropy decoded from a received bitstream by entropy decoding unit 150 before being sent to depth processing unit 165 in the decoding process.

[0179] In one example, in generating the list of candidates, depth processing unit 165 may determine that a texture candidate that is co-located with the depth block is not a viable candidate, and replace the texture candidate that is co-located with the depth block with the at least one texture candidate that is not co-located with the depth block. Again, a candidate may not be a viable candidate for various reasons, such as when it is coded in an intra mode, when it has a motion vector equal to zero, or any other reason where both video encoder 20 and the video decoder 30 are programmed to know that the candidate cannot provide an accurate motion vector for coding the depth block.

[0180] In some examples, the list generated by depth processing unit 165 may also include a texture candidate that is co-located with the depth block. In other words, in some cases the list may include both a texture candidate that is co-located with the depth block and one or more other texture candidates that are not co-located with the depth block, while in other cases, the list may include one or more other texture candidates that are not co-located with the depth block only when the texture candidate that is co- located with the depth block is excluded from the list.

[0181] As one example, the at least one texture candidate that is not co-located with the depth block may be a bottom right candidate relative to a texture candidate that is co- located with the depth block. A variety of other candidates, with other positions relative to a texture candidate that is co-located with the depth block, may also be used by depth processing unit 165.

[0182] In another example, the at least one texture candidate that is not co-located with the depth block may comprise a shifted candidate that is shifted horizontally, vertically or both horizontally and vertically, relative to a texture candidate that is co-located with the depth block. For example, the shifted texture candidate may be shifted horizontally and vertically by M pixels, wherein M is an integer. M may be equal to 32, 16, 8 or another integer value, usually an even value and usually a value that is divisible by 4, although the techniques are not necessarily limited in this respect. Alternatively, the shifted texture candidate may be shifted horizontally by M pixels and vertically by N pixels, wherein M and N are different integers.

[0183] In many examples, the at least one texture candidate that is not co-located with the depth block comprises a plurality of texture candidates that are not co-located with the depth block. One of the plurality of texture candidates that are not co-located with the depth block may be a first ordered candidate in the list (i.e., the first one in the list). In some cases, another of the texture candidates that are not co-located with the depth block may be ordered second in the list, or possibly later in the list and e.g., after at least one spatial candidate in the list.

[0184] Depth processing unit 165 may also prune the list such that when two or more texture candidate that are not co-located with the depth block have a same motion vector, at least one of the two or more texture candidate that are not co-located with the depth block is excluded from the list. This pruning by depth processing unit 165 may avoid the case where duplicate candidates provide the same information for coding the depth block in a merge/skip mode (or similar mode such as AMVP mode).

[0185] In some examples, depth processing unit 165 may determine whether one or more spatial candidates are viable candidates, and if one or more of the spatial candidates are not viable, insert into the list another texture candidate that is not co- located with the depth block.

[0186] Furthermore, in some examples, in generating the list of candidates depth processing unit 165 may determine that a texture candidate that is co-located with the depth block is not a viable candidate, determine whether a bottom right texture candidate is a viable candidate, and if the bottom right texture candidate is a viable candidate, replace the texture candidate that is co-located with the depth block with the bottom right texture candidate. In this case, upon determining that the bottom right texture candidate is a viable candidate, depth processing unit 165 may determine whether a shifted texture candidate is a viable candidate, and if the shifted texture candidate is a viable candidate, replace the texture candidate that is co-located with the depth block with the shifted texture candidate. In other words, the bottom right candidate may be given higher priority over one or more shifted candidates by depth processing unit 165.

[0187] In other examples, one or more shifted candidates or other non-co-located texture candidates (right, bottom, top, left, top left, top right, or bottom left) could also be given higher priority over the bottom right candidate. Any of these non-co-located texture candidates could be used in various examples, although the specific technique that gives first priority to the co-located candidate (if viable), next priority to the bottom right texture candidate (if viable), followed by next priority to one or more shifted candidates (if viable) may result in desirable coding efficiency and relatively simple implementation.

[0188] Continuing reference is now made to FIG. 12. Reconstruction unit 158 may use the luma, Cb and Cr transform blocks associated with TUs of a CU and the predictive luma, Cb and Cr blocks of the PUs of the CU, i.e., either intra-prediction data or inter- prediction data, as applicable, to reconstruct the luma, Cb and Cr coding blocks of the CU. For example, reconstruction unit 158 may add samples of the luma, Cb and Cr transform blocks to corresponding samples of the predictive luma, Cb and Cr blocks to reconstruct the luma, Cb and Cr coding blocks of the CU.

[0189] Filter unit 160 may perform a deblocking operation to reduce blocking artifacts associated with the luma, Cb and Cr coding blocks of the CU. Video decoder 30 may store the luma, Cb and Cr coding blocks of the CU in decoded picture buffer 162. Decoded picture buffer 162 may provide reference pictures for subsequent motion compensation, intra prediction, and presentation on a display device, such as display device 32 of FIG. 10. For instance, video decoder 30 may perform, based on the luma, Cb and Cr blocks in decoded picture buffer 162, intra prediction or inter prediction operations on PUs of other CUs. In this way, video decoder 30 may extract, from the bitstream, transform coefficient levels of the significant luma coefficient block, inverse quantize the transform coefficient levels, apply a transform to the transform coefficient levels to generate a transform block, generate, based at least in part on the transform block, a coding block, and output the coding block for display.

[0190] FIG. 13 is a flow diagram illustrating a coding technique for coding (i.e., encoding or decoding) a depth block according to a merge mode or skip mode, or possibly according to an AMVP mode. As shown in FIG. 13, a video coder (i.e., an encoder or decoder or device that includes an encoder or decoder) generates a list of candidates for coding a depth block (131). The coding may be performed according to a merge mode, a skip mode, possibly an AMVP mode, or any other mode in which a list of candidates may be used. The list of candidates includes at least non-co-located texture candidate (131). The video coder then codes the depth block based on the list (132).

[0191] As described herein, when generating the list (131), the video coder may determine that a texture candidate that is co-located with the depth block is not a viable candidate, and replace the texture candidate that is co-located with the depth block with the at least one texture candidate that is not co-located with the depth block.

Alternatively, the list may include a texture candidate that is co-located with the depth block, in which case the non-co-located candidate may be another possible selection within the list that includes both candidates, and possibly other spatial or temporal depth candidates.

[0192] In some specific examples, the at least one texture candidate that is not co- located with the depth block may comprise one of: a bottom right candidate relative to a texture candidate that is co-located with the depth block, and a shifted candidate that is shifted horizontally and/or vertically relative to a texture candidate that is co-located with the depth block. Other examples are described herein and may be used within the process shown in FIG. 13.

[0193] FIG. 14 is a flow diagram illustrating a decoding technique for decoding a depth block according to a merge mode or skip mode. As shown in FIG. 14, depth processing unit 165 of video decoder 30 receives a syntax element that defines a selection from the list (141). The syntax element may be entropy decoded from a received bitstream by entropy decoding unit 150 before being sent to depth processing unit 165 in the decoding process.

[0194] Depth processing unit 165 generates a list of candidates for decoding the depth block, wherein the list includes a non-co-located texture candidate (142). The list of candidates may be a list defined according to a merge mode or a skip mode, or another mode that uses such lists. Depth processing unit 165 decodes the depth block based on the selected candidate from the list identified by the syntax element (143).

[0195] In generating the list of candidates (142), depth processing unit 165 may determine that a texture candidate that is co-located with the depth block is not a viable candidate, and replace the texture candidate that is co-located with the depth block with the at least one texture candidate that is not co-located with the depth block. Again, a candidate may not be a viable candidate for various reasons, such as when it is coded in an intra mode, when it has a motion vector equal to zero, or any other reason where both video encoder 20 and the video decoder 30 are programmed to know that the candidate cannot provide an accurate motion vector for coding the depth block.

[0196] In some examples, the list generated (142) by depth processing unit 165 may also include a texture candidate that is co-located with the depth block. In other words, in some cases the list may include both a texture candidate that is co-located with the depth block and one or more other texture candidates that are not co-located with the depth block, while in other cases, the list may include one or more other texture candidates that are not co-located with the depth block only when the texture candidate that is co-located with the depth block is excluded from the list.

[0197] As one example, the at least one texture candidate that is not co-located with the depth block may be a bottom right candidate relative to a texture candidate that is co- located with the depth block. A variety of other candidates, with other positions relative to a texture candidate that is co-located with the depth block, may also be used by depth processing unit 165.

[0198] In another example, the at least one texture candidate that is not co-located with the depth block may comprise a shifted candidate that is shifted horizontally, vertically or both horizontally and vertically, relative to a texture candidate that is co-located with the depth block. For example, the shifted texture candidate may be shifted horizontally and vertically by M pixels, wherein M is an integer. M may be equal to 32, 16, 8 or another integer value, usually an even value and usually a value that is divisible by 4, although the techniques are not necessarily limited in this respect. Alternatively, the shifted texture candidate may be shifted horizontally by M pixels and vertically by N pixels, wherein M and N are different integers.

[0199] In many examples, the at least one texture candidate that is not co-located with the depth block comprises a plurality of texture candidates that are not co-located with the depth block. One of the plurality of texture candidates that are not co-located with the depth block may be a first ordered candidate in the list (i.e., the first one in the list). In some cases, another of the texture candidates that are not co-located with the depth block may be ordered second in the list, or possibly later in the list and e.g., after at least one spatial candidate in the list. [0200] In generating the list (142), depth processing unit 165 may also prune the list such that when two or more texture candidate that are not co-located with the depth block have a same motion vector, at least one of the two or more texture candidate that are not co-located with the depth block is excluded from the list. This pruning by depth processing unit 165 may avoid the case where duplicate candidates provide the same information for coding the depth block in a merge mode or skip mode.

[0201] In some examples, in generating the list (142), depth processing unit 165 may determine whether one or more spatial candidates are viable candidates, and if one or more of the spatial candidates are not viable, insert into the list another texture candidate that is not co-located with the depth block.

[0202] Furthermore, in some examples, in generating the list of candidates (142), depth processing unit 165 may determine that a texture candidate that is co-located with the depth block is not a viable candidate, determine whether a bottom right texture candidate is a viable candidate, and if the bottom right texture candidate is a viable candidate, replace the texture candidate that is co-located with the depth block with the bottom right texture candidate. In this case, upon determining that the bottom right texture candidate is a viable candidate, depth processing unit 165 may determine whether a shifted texture candidate is a viable candidate, and if the shifted texture candidate is a viable candidate, replace the texture candidate that is co-located with the depth block with the shifted texture candidate. In other words, the bottom right candidate may be given higher priority over one or more shifted candidates by depth processing unit 165.

[0203] Moreover, in other examples, one or more shifted candidates or other non-co- located texture candidates (right, bottom, top, left, top left, top right, or bottom left) could also be given higher priority over the bottom right candidate. Any of these non- co-located texture candidates could be used in various examples, although the specific technique that gives first priority to the co-located candidate (if viable), next priority to the bottom right texture candidate (if viable), followed by next priority to one or more shifted candidates (if viable) may result in desirable coding efficiency and relatively simply implementation.

[0204] FIG. 15 is a flow diagram illustrating an encoding technique for encoding a depth block according to a merge mode or skip mode. As shown in FIG. 15, depth processing unit 125 of video encoder 20 generates a list of candidates for encoding the depth block, wherein the list includes a non-co-located texture candidate (151). The list of candidates may be a list defined according to a merge mode or a skip mode, or another mode that uses such lists.

[0205] Depth processing unit 125 selects one of the candidates to be used to encode the depth block based on analysis of the candidates (152). This analysis may comprise a rate-distortion analysis or possibly just an analysis that minimizes distortion. Depth processing unit 125 generates a syntax element that defines the selection (153), and this syntax element may be entropy encoded by entropy encoding unit 118 and included in a coded bitstream.

[0206] The same process for generating the list of candidates may be performed by encoder 20 and decoder 20. Encoder 20 selects from the list based on an analysis of the coding efficiency (e.g., via a rate-distortion analysis or a distortion minimization analysis). Upon making the selection, encoder 20 includes a syntax element in a coded bitstream that identifies this selection.

[0207] On the decoder side, decoder 30 receives the syntax element that identifies the selection, which is part of the coded bitstream. Decoder 30 performs the same list generation process as that performed by encoder 20 and makes a selection from the list based on the syntax element. In this way, the same selection chosen by encoder 20 in the encoding process is used by decoder 30 in the decoding process.

[0208] Consistent with the technique of FIG. 15, the various other techniques and examples described above, e.g., with reference to FIG. 14, may also be applied. In addition, the list generation process (151 in FIG. 15 or 142 of FIG. 14) may apply any of the techniques or examples described herein. These details for list generation have been described above and will not be repeated again in this section. Any of the list generation techniques described above may be examples that are applicable to list generation process (151) with the encoding process shown in FIG. 15.

[0209] In one or more examples, the functions described herein may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit.

Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer- readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

[0210] By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but are instead directed to non-transient, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0211] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term "processor," as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0212] The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

[0213] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method of decoding depth data associated with three-dimensional (3D) video data, the method comprising:

generating a list of candidates for decoding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block; and

decoding the depth block based on the list.

2. The method of claim 1, further comprising:

receiving a syntax element that defines a selection from the list; and

decoding the depth block based on the selection from the list.

3. The method of claim 1, wherein generating the list of candidates includes:

determining that a texture candidate that is co-located with the depth block is not a viable candidate; and

replacing the texture candidate that is co-located with the depth block with the at least one texture candidate that is not co-located with the depth block.

4. The method of claim 1, wherein the list also includes a texture candidate that is co-located with the depth block.

5. The method of claim 1, wherein the at least one texture candidate that is not co- located with the depth block is a bottom right candidate relative to a texture candidate that is co-located with the depth block.

6. The method of claim 1, wherein the at least one texture candidate that is not co- located with the depth block is a shifted candidate that is shifted horizontally and vertically relative to a texture candidate that is co-located with the depth block.

7. The method of claim 6, wherein the shifted texture candidate is shifted horizontally and vertically by M pixels, wherein M is an integer.

8. The method of claim 7, wherein M is equal to 32, 16 or 8.

9. The method of claim 6, wherein the shifted texture candidate is shifted horizontally by M pixels and vertically by N pixels, wherein M and N are different integers.

10. The method of claim 1, wherein the at least one texture candidate that is not co- located with the depth block is a shifted candidate that is shifted either horizontally or vertically relative to a texture candidate that is co-located with the depth block.

11. The method of claim 1 , wherein the at least one texture candidate that is not co- located with the depth block comprises a plurality of texture candidates that are not co- located with the depth block.

12. The method of claim 11, wherein one of the plurality of texture candidates that are not co-located with the depth block is a first ordered candidate in the list, and wherein another of the texture candidates that are not co-located with the depth block is ordered after at least one spatial candidate in the list.

13. The method of claim 1, further comprising pruning the list such that when two or more texture candidate that are not co-located with the depth block have a same motion vector, at least one of the two or more texture candidate that are not co-located with the depth block is excluded from the list.

14. The method of claim 1, further comprising determining whether one or more spatial candidates are viable candidates, and if one or more of the spatial candidates are not viable, inserting into the list another texture candidate that is not co-located with the depth block.

15. The method of claim 1, wherein generating the list of candidates includes:

determining that a texture candidate that is co-located with the depth block is not a viable candidate; and determining whether a bottom right texture candidate is a viable candidate, and if the bottom right texture candidate is a viable candidate, replacing the texture candidate that is co-located with the depth block with the bottom right texture candidate.

16. The method of claim 15, further comprising:

upon determining that the bottom right texture candidate is a viable candidate, determining whether a shifted texture candidate is a viable candidate, and if the shifted texture candidate is a viable candidate, replacing the texture candidate that is co-located with the depth block with the shifted texture candidate.

17. A method of encoding depth data associated with three-dimensional (3D) video data, the method comprising:

generating a list of candidates for encoding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block; and

encoding the depth block based on the list.

18. The method of claim 17, wherein encoding the depth block based on the list includes:

selecting one of the candidates to encode the depth block; and

generating a syntax element that defines the selection.

19. The method of claim 17, wherein generating the list of candidates includes: determining that a texture candidate that is co-located with the depth block is not a viable candidate; and

20. The method of claim 17, wherein the list also includes a texture candidate that is co-located with the depth block.

21. The method of claim 17, wherein the at least one texture candidate that is not co- located with the depth block is a bottom right candidate relative to a texture candidate that is co-located with the depth block.

22. The method of claim 17, wherein the at least one texture candidate that is not co- located with the depth block is a shifted candidate that is shifted horizontally and vertically relative to a texture candidate that is co-located with the depth block.

23. The method of claim 22, wherein the shifted texture candidate is shifted horizontally and vertically by M pixels, wherein M is an integer.

24. The method of claim 23, wherein M is equal to 32, 16 or 8.

25. The method of claim 22, wherein the shifted texture candidate is shifted horizontally by M pixels and vertically by N pixels, wherein M and N are different integers.

26. The method of claim 17, wherein the at least one texture candidate that is not co- located with the depth block is a shifted candidate that is shifted either horizontally or vertically relative to a texture candidate that is co-located with the depth block.

27. The method of claim 17, wherein the at least one texture candidate that is not co- located with the depth block comprises a plurality of texture candidates that are not co- located with the depth block.

28. The method of claim 27, wherein one of the plurality of texture candidates that are not co-located with the depth block is a first ordered candidate in the list, and wherein another of the texture candidates that are not co-located with the depth block is ordered after at least one spatial candidate in the list.

29. The method of claim 17, further comprising pruning the list such that when two or more texture candidate that are not co-located with the depth block have a same motion vector, at least one of the two or more texture candidate that are not co-located with the depth block is excluded from the list.

30. The method of claim 17, further comprising determining whether one or more spatial candidates are viable candidates, and if one or more of the spatial candidates are not viable, inserting into the list another texture candidate that is not co-located with the depth block.

31. The method of claim 17, wherein generating the list of candidates includes: determining that a texture candidate that is co-located with the depth block is not a viable candidate; and

determining whether a bottom right texture candidate is a viable candidate, and if the bottom right texture candidate is a viable candidate, replacing the texture candidate that is co-located with the depth block with the bottom right texture candidate.

32. The method of claim 31, further comprising:

33. A device that codes depth data associated with three-dimensional (3D) video data, the device comprising:

a depth processing unit that:

generates a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block; and

codes the depth block based on the list.

34. The device of claim 33, wherein the device decodes the depth data, and wherein the depth processing unit:

receives a syntax element that defines a selection from the list; and

decodes the depth block based on the selection from the list.

35. The device of claim 33, wherein the device encodes the depth data, and wherein the depth processing unit:

selects one of the candidates to encode the depth block; and

generates a syntax element that defines the selection.

36. The device of claim 33, wherein in generating the list of candidates, the depth processing unit:

determines that a texture candidate that is co-located with the depth block is not a viable candidate; and

replaces the texture candidate that is co-located with the depth block with the at least one texture candidate that is not co-located with the depth block.

37. The device of claim 33, wherein the list also includes a texture candidate that is co-located with the depth block.

38. The device of claim 33, wherein the at least one texture candidate that is not co- located with the depth block is a bottom right candidate relative to a texture candidate that is co-located with the depth block.

39. The device of claim 33, wherein the at least one texture candidate that is not co- located with the depth block is a shifted candidate that is shifted horizontally and vertically relative to a texture candidate that is co-located with the depth block.

40. The device of claim 39, wherein the shifted texture candidate is shifted horizontally and vertically by M pixels, wherein M is an integer.

41. The device of claim 40, wherein M is equal to 32, 16 or 8.

42. The device of claim 39, wherein the shifted texture candidate is shifted horizontally by M pixels and vertically by N pixels, wherein M and N are different integers.

43. The device of claim 33, wherein the at least one texture candidate that is not co- located with the depth block is a shifted candidate that is shifted either horizontally or vertically relative to a texture candidate that is co-located with the depth block.

44. The device of claim 33, wherein the at least one texture candidate that is not co- located with the depth block comprises a plurality of texture candidates that are not co- located with the depth block.

45. The device of claim 44, wherein one of the plurality of texture candidates that are not co-located with the depth block is a first ordered candidate in the list, and wherein another of the texture candidates that are not co-located with the depth block is ordered after at least one spatial candidate in the list.

46. The device of claim 33, wherein the depth processing unit prunes the list such that when two or more texture candidate that are not co-located with the depth block have a same motion vector, at least one of the two or more texture candidate that are not co-located with the depth block is excluded from the list.

47. The device of claim 33, wherein the depth processing unit determines whether one or more spatial candidates are viable candidates, and if one or more of the spatial candidates are not viable, inserting into the list another texture candidate that is not co- located with the depth block.

48. The device of claim 33, wherein in generating the list of candidates the depth processing unit:

determines whether a bottom right texture candidate is a viable candidate, and if the bottom right texture candidate is a viable candidate, replaces the texture candidate that is co-located with the depth block with the bottom right texture candidate.

49. The device of claim 48, wherein the depth processing unit:

upon determining that the bottom right texture candidate is a viable candidate, determines whether a shifted texture candidate is a viable candidate, and if the shifted texture candidate is a viable candidate, replaces the texture candidate that is co-located with the depth block with the shifted texture candidate.

50. A non-transitory computer-readable storage comprising instructions that upon execution cause one or more processors to:

generate a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block; and

code the depth block based on the list.

51. The non-transitory computer-readable storage of claim 50, wherein in generating the list of candidates, the instructions cause the one or more processors to:

determine that a texture candidate that is co-located with the depth block is not a viable candidate; and

replace the texture candidate that is co-located with the depth block with the at least one texture candidate that is not co-located with the depth block.

52. The non-transitory computer-readable storage of claim 50, wherein the list also includes a texture candidate that is co-located with the depth block.

53. The non-transitory computer-readable storage claim 50, wherein the at least one texture candidate that is not co-located with the depth block is one of:

a bottom right candidate relative to a texture candidate that is co-located with the depth block; and

a shifted candidate that is shifted horizontally and/or vertically relative to a texture candidate that is co-located with the depth block.

54. A device comprising:

means for generating a list of candidates for coding a depth block according to a merge mode or a skip mode, wherein the list of candidates includes at least one texture candidate that is not co-located with the depth block; and

means for coding the depth block based on the list.

55. The device of claim 54, wherein the means for generating the list includes: means for determining that a texture candidate that is co-located with the depth block is not a viable candidate; and

means for replacing the texture candidate that is co-located with the depth block with the at least one texture candidate that is not co-located with the depth block.

56. The device of claim 54, wherein the list also includes a texture candidate that is co-located with the depth block.

57. The device of claim 54, wherein the at least one texture candidate that is not co- located with the depth block is one of: