Reducing/Eliminating visual artifacts in HEVC by Deblocking filter Submitted By: Harshal Shah Under the guidance of Dr. K. R. Rao

HEVC Overview [2]  HEVC–Most recent standard in video compression technology. Also known as H.265.  Provides around 50% bit-rate reduction while maintaining the same subjective video quality relative to its predecessor H.264  Developed by the ISO and ITU-T 2/18/2014 EE-5359 : Interim report Presentation 2

HEVC Encoder Block Diagram [1] 2/18/2014 EE-5359 : Interim report Presentation 3

 Each picture is split into block-shaped regions, with the exact block partitioning being conveyed to the decoder.  The first picture of a video sequence (and the first picture at each clean random access point into a video sequence) is coded using only intrapicture prediction  For all remaining pictures of a sequence or between random access points, interpicture temporally predictive coding modes are typically used for most blocks.  The encoding process for interpicture prediction consists of choosing motion data comprising the selected reference picture and motion vector (MV) to be applied for predicting the samples of each block. 2/21/2013 EE-5359 : Interim report Presentation 4

HEVC Decoder Block Diagram [1] 2/18/2014 EE-5359 : Interim report Presentation 5

Why HEVC ?  To ensure the highest level of compression efficiency, and support for parallel processing, some parts of HEVC have been significantly modified compared with previous generations of hybrid block-based codecs. [3]  For most of the previous MPEG-x and H.26x codecs, the largest entity that could be independently encoded was a macro block (16 × 16 pixels) [10]. For HEVC, the picture is split into coding-tree units (CTUs) with a maximum size of 64 × 64 pixels. [3] 2/18/2014 EE-5359 : Interim report Presentation 6

Blocking Artifacts [10]  Discontinuities can occur in the reconstructed signal at the block boundaries. Visible discontinuities at the block boundaries are blocking artifacts.  Degrades the quality of video and image  Most annoying artifacts in video and image compression coding. 2/18/2014 EE-5359 : Interim report Presentation 7

Example of block boundary with blocking artifact [11] 2/18/2014 EE-5359 : Interim report Presentation 8

Deblocking filter [12]  Detects artifacts at the coded block boundaries and attenuates them by applying a selected filter.  The deblocking filter in HEVC has been designed to improve the subjective quality while reducing the complexity.  The HEVC deblocking filter is less complex as compared to the H.264/AVC deblocking filter, while still having the capability to improve the subjective and objective quality. 2/18/2014 EE-5359 : Interim report Presentation 9

Processing flow of deblocking filter [13]  Firstly, the decision should be made that whether the current boundary is a boundary of CU, PU or TU. If not, the filtering processing should be not applied to the current boundary.  Boundary strength (BS) reflects how strong the filtering is needed for the boundary.  Threshold values β and tc which are used for filter on/off decision, strong/weak filter selection. 2/18/2014 EE-5359 : Interim report Presentation 10

Sample Adaptive Offset (SAO) in HEVC : SAO is a process that modifies the decoded samples by conditionally adding an offset value to each sample after the application of the deblocking filter, based on values in look-up tables transmitted by the encoder. The key idea of SAO is to reduce sample distortion by first classifying reconstructed samples into different categories, obtaining an offset for each category, and then adding the offset to each sample of the category. 2/21/2013EE-5359 : Interim report Presentation11

Block Diagram of Deblocking filter As shown in Fig. 1, SAO is located after DF and also belongs to in-loop filtering. The concept of SAO is to reduce mean sample distortion of a region by first classifying the region samples into multiple categories with a selected classifier, obtaining an offset for each category, and then adding the offset to each sample of the category, where the classifier index and the offsets of the region are coded in the bit stream 2/21/2013 EE-5359 : Interim report Presentation 12

Sample Processing in SAO SAO may use different offsets sample by sample in a region depending on the sample classification, and SAO parameters are adapted from region to region. Two SAO types that can satisfy the requirements of low complexity are adopted in HEVC: edge offset (EO) and band offset (BO). For EO, the sample classification is based on comparison between current samples and neighboring samples. For BO, the sample classification is based on sample values. 2/21/2013 EE-5359 : Interim report Presentation 13 Figure is of Four 1-D directional patterns for EO sample classification: horizontal (EO class = 0), vertical (EO class = 1), 135° diagonal (EO class = 2), and 45° diagonal (EO class = 3).

Proposed Work  Study and implementation of Deblocking filters to reduce the visual artifacts in HEVC.  study the working and performance analysis of deblocking filter algorithm in HEVC and compare it with H.264.  Implementing it on HM13.0 reference software. 2/18/2014 EE-5359 : Interim report Presentation 14

1. INTRA 2/21/2013EE-5359 : Project Proposal Presentation15 INTRA TIME (Sec)BD bitrate (KBPS)PSNR(Db) DB Off DB ON encoder_intra_main.cfg with Default and DB ON for bus.qcif ( QP=32 )

2/21/2013EE-5359 : Project Proposal Presentation16

2. LOW DELAY 2/21/2013EE-5359 : Project Proposal Presentation17 Low Delay TIME (Sec)BD bitrate (KBPS)PSNR(Db) DB Off DB ON encoder_lowdelay_main.cfg with Default and DB ON for bus.qcif ( QP=32 )

2/21/2013EE-5359 : Project Proposal Presentation18

List of ACRONYMS CU: Coding unit. CABAC: Context adaptive binary arithmetic coding CTUs: Coding tree units. DSPs : Digital signal processors FDCT: Fast discrete cosine transform. HDTV: High definition television HEVC: High Efficiency Video Coding. ITU: International Telecommunication Union ITU-TITU Telecommunication Standardization Sector JVT - VT: Joint collaborative team on video coding MSE: Mean square error. MPEG: Moving picture experts group. PU: Prediction unit PSNR: Peak signal to noise ratio. QVGA: Quarter Video Graphics Array. QCIF: Quarter common intermediate format. QP: Quantization parameter VCEG: Video Coding Experts Group 2/21/2013 EE-5359 : Interim report Presentation 19

References [1] G.J. Sullivan, et al “Overview of the high efficiency video coding (HEVC) standard”, IEEE Trans. circuits and systems for video technology, vol. 22, no.12, pp – 1668, Dec [2] P.Topiwala et al, “Performance comparison of JPEG2000 and H.264/AVC high profile intra- frame coding on HD video sequences”, SPIE int‘l symposium, digital image processing, vol. 6312, no.8, pp , Aug [3] Q.Cai, et al, “Lossy and lossless intra coding performance evaluation: HEVC, H.264/AVC, JPEG 2000 and JPEG LS”. Published in signal and information processing association annual summit and conference, vol.9, no.12, pp.1-9, Dec [4] K.R. Rao, D. N. Kim and J. J. Hwang, “Video Coding standards”, pp , Springer [5] “High Efficiency Video Coding HEVC / H.265” article Available Vcodex website 2/18/2014 EE-5359 : Interim report Presentation 20

[6] “Next generation video compression – Ericsson Review The Communications Journal” Available website: compression_ _chttp:// compression_ _c [7] L. Zhao et al, “Fast mode decision algorithm for intra prediction in HEVC”, Conference Article no , IEEE Visual Communications and Image Processing, 6-9 Nov [8]JCT-VC, “WD1: Working Draft 1 of High-Efficiency Video Coding”, JCTVC-C403, JCT-VC Meeting, Guangzhou, October [9] G.J. Sullivan et al, “Standardized Extensions of High Efficiency Video Coding (HEVC)”, IEEE Journal on Selected Topics in signal Processing, vol. 7, pp , December [10]W.Y. Wei, "Deblocking Algorithms in Video and Image Compression Coding." Graduate Institute of Communication Engineering, National Taiwan University, Taipei, Taiwan, ROC 2/21/2013 EE-5359 : Interim report Presentation 21

[11] A. Norkin et al, “HEVC Deblocking Filter”, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 22, No. 12, pp , Dec [12]W. Shen et al, “A high-throughput VLSI architecture for deblocking filter in HEVC”,“IEEE International Symposium on Circuits and Systems (ISCAS)”, pp , May 2013 [13] W. Shen et al, “A 64 Cycles/MB, Luma- Chroma Parallelized H.264/AVC Deblocking Filter for 4Kx2K Applications”, “IEEE International Symposium on Circuits and Systems (ISCAS)”, vol.E95-C, no.4, pp , April [14] K.Xu, “A Five-Stage Pipeline, 204 Cycles/MB, Single-Port SRAM-Based Deblocking Filter for H.264/AVC,”, IEEE Transactions on Circuits and Systems for Video Technology, vol.18, no.3, pp , March [15] P. List et al, “Adaptive deblocking filter,” IEEE Trans. Circuits Syst. Video Technol., vol. 13, no. 7, pp. 614–619, July /21/2013 EE-5359 : Interim report Presentation 22

[16] C.-M. Fu et al, “Sample adaptive offset in the HEVC standard,” IEEE Transactions on Circuits and Systems for Video Technology., vol. 22, no. 12, pp. 1755–1764, Dec [17] ITU-T: "H.265 : High efficiency video coding", April 2013.To access it, go to [18] HEVC Reference Software HM [19] E.Ozcan et al, “A high performance deblocking filter hardware for High Efficiency Video Coding”, rd International Conference on Field Programmable Logic and Applications, pp 1-4, Sept [20] Required test sequence 2/21/2013EE-5359 : Project Proposal Presentation23