High Efficiency Video Coding Screen Content Coding Research Articles

Decision Tree Models and Early Splitting Termination in Screen Content Extension of High Efficiency Video Coding

A Screen Content (SC) extension to the High Efficiency Video Coding (HEVC) standard has been developed to improve the encoding of SC sequences. SC scenes are rich in repeated patterns, non-noisy regions, sharp-edge areas, and blocks with limited colors, which differ from Natural Content (NC) videos. For the SC Coding (SCC) process, new tools have been incorporated into the HEVC SC extension such as Intra Bock Copy (IBC) and Palette (PLT); these tools improve the compression accuracy at the expense of high computational complexity. In this paper, we present a framework to reduce the encoding time of SC encoders by exploiting the characteristics of the SC blocks. The framework contains two techniques. The first is called Decision Tree Models (DTM), and it includes decision tree-based classification blocks to reduce the number of executed modes. In the DTM technique, the features of each Coding Unit (CU) are extracted and trained to build the classification trees. To further speed up the encoding process, a second technique called Early Splitting Termination (EST) is suggested to stop the normal splitting process of homogeneous blocks by measuring the luminance contrast inside the blocks. Compared with the HM-16.7+SCM-6 reference test model, the proposed framework can provide a 35.96% encoding time reduction on average with only a 0.89% increase in Bjontegaard Delta bit-rate (BD-Rate) under the All-Intra (AI) configuration profile, which outperforms the approaches in the literature. In addition, the proposed framework reduces the encoding time by 54.3% on average for a number of NC sequences recommended for conventional HEVC test, with only 0.74% increment in the BD-Rate. For further speeding up, the proposed scheme has been integrated with an existing approach. Consequently, a 45.84% reduction in time complexity is obtained with a BD-Rate increase of only 1.3%.

Efficient intra mode decision for low complexity HEVC screen content compression.

High efficiency video coding screen content coding (HEVC-SCC) extension is the latest HEVC development to improve the compression performance of screen content (SC) video. Similar to HEVC, the intra mode selection in HEVC-SCC is performed all the coding unit (CU) partitions to find the least rate distortion (RD) cost. Furthermore, additional intra tools are introduced to improve HEVC-SCC coding efficiency. However, these new tools could cause high computation complexity which restricts HEVC-SCC from ongoing applications. To solve the problem, an efficient intra mode decision for HEVC-SCC that adaptively utilizes the texture complexity of SC treeblock is proposed. The texture complexity of a SC treeblock is first analyzed according to the variation degree of the luminance value. And then, two efficient approaches are proposed based on the constructed model, which are early CU depth level determination and adaptive intra mode selection. Experimental results demonstrate that the proposed method can save 48.5% encoder runtime while keeping nearly the same coding efficiency as the HEVC-SCC encoders.

Fast Palette Mode Decision Methods for Coding Game Videos With HEVC-SCC

The live broadcasting of game playing is becoming more and more popular. The game video is one of the typical video data which should be coded with high efficiency video coding-screen content coding (HEVC-SCC). In HEVC-SCC, the palette mode is an important technique which can effectively enhance the coding performance. However, this technique also demands high-coding computation. In this paper, we propose a fast palette mode pre-decision method based on the analysis of the color complexity of the video data. Considering only the coding computation of palette mode of HEVC-SCC, our algorithm saves about 74.24% computation in the experiments of game videos. Whereas, the BDBR only increases by about 0.36% and the BDPSNR decreases by about 0.03 dB on average.

Mode Skipping for HEVC Screen Content Coding via Random Forest

Screen content coding (SCC) is the extension to high-efficiency video coding (HEVC) for compressing screen content videos. New coding tools, intrablock copy (IBC), and palette (PLT) modes, are introduced to encode screen content (SC) such as texts and graphics. The IBC mode is used for encoding repeating patterns by performing block matching within the same frame, while the PLT mode is designed for SC with few distinct colors by coding the major colors and their corresponding locations using an index map. However, the use of IBC and PLT modes increases the encoder complexity remarkably though coding efficiency can be improved. Therefore, we propose to have a mode skipping approach to reduce the encoder complexity of SCC by making use of SC characteristics, neighbor coding unit (CU) correlations, and intermediate cost information via random forest (RF). Detailed feature analyses and sample preparation are also described. A novel hyperparameter tuning approach with the consideration of coding bitrate and encoding time is proposed for RFs at each CU size to further boost the encoding process. Experimental results show that our proposed approach can obtain 45.06% average encoding time reduction with only a 1.08% increase in Bjontegaard delta bitrate. Average encoding time can even be reduced to 58.57% by regulating the hyperparameters.

Fast intraprediction for high-efficiency video coding screen content coding by content analysis and dynamic thresholding

Fast intraprediction for high-efficiency video coding screen content coding by content analysis and dynamic thresholding

Fast Hash-Based Inter-Block Matching for Screen Content Coding

In the latest High Efficiency Video Coding (HEVC) development, i.e., HEVC screen content coding extensions (HEVC-SCC), a hash-based inter-motion search/block matching scheme is adopted in the reference test model, which brings significant coding gains to code screen content. However, the hash table generation itself may take up to half the encoding time and is thus too complex for practical usage. In this paper, we propose a hierarchical hash design and the corresponding block matching scheme to significantly reduce the complexity of hash-based block matching. The hierarchical structure in the proposed scheme allows large block calculation to use the results of small blocks. Thus, we avoid redundant computation among blocks with different sizes, which greatly reduces complexity without compromising coding efficiency. The experimental results show that compared with the hash-based block matching scheme in the HEVC-SCC test model (SCM)-6.0, the proposed scheme reduces about 77% of hash processing time, which leads to 12% and 16% encoding time savings in random access (RA) and low-delay B coding structures. The proposed scheme has been adopted into the latest SCM. A parallel implementation of the proposed hash table generation on graphics processing unit (GPU) is also presented to show the high parallelism of the proposed scheme, which achieves more than 30 frames/s for 1080p sequences and 60 frames/s for 720p sequences. With the fast hash-based block matching integrated into x265 and the hash table generated on GPU, the encoder can achieve 11.8% and 14.0% coding gains on average for RA and low-delay P coding structures, respectively, for real-time encoding.

Fast intra bit rate transcoding for HEVC screen content coding

This study presents an efficient fast bit rate transcoding method for high-efficiency video coding (HEVC) screen content coding (SCC). It utilises the correlation between the current coding unit (CU) and the corresponding decoded CU to skip the normal intra mode or intra block copy mode. Furthermore, quantisation parameter values are also incorporated into the algorithm for better performance. In addition, a fast scheme is designed to skip partial prediction unit modes to accelerate the entire transcoding process. Experimental results show that, compared with the original HEVC SCC reference software (SCM-3.0), the proposed fast intra transcoding algorithms achieve 45.09% transcoding time reduction with only 1.78% Bjotegaard delta bit rate increment for the all-intra case.

A Universal String Matching Approach to Screen Content Coding

This paper proposes a universal string matching (USM) approach to screen content coding (SCC). USM uses a primary reference buffer and a secondary reference buffer for string matching and includes three modes: general string (GS) mode, constrained string 1 (CS1) mode, and constrained string 2 (CS2) mode. The CS1 mode and CS2 mode are constrained cases of the GS mode. Due to the diversity of the screen content, each of the three modes plays an indispensable role in coding some types of screen content . When using USM to code a coding unit (CU) , one of the three modes is selected to code the CU. Compared with high-efficiency video coding (HEVC) SCC reference software HM-16.6 + SCM-5.2 of full frame search range for intrablock copy, USM achieves an average Y BD-rate of –28.4% for five text and graphics with motion (TGM) sequences from the audio video coding standard SCC common test condition (CTC) test suite and –5.8% for eight TGM test sequences from the HEVC SCC CTC test suite in all intraconfigurations, with a nearly 10% decrease in encoding runtime and almost the same decoding runtime.

Weighted Rate-Distortion Optimization for Screen Content Coding

Unlike camera-captured video, screen content (SC) often contains a lot of repeating patterns, which makes some blocks used as references much more important than others. However, conventional rate-distortion optimization (RDO) schemes in video coding do not consider the dependence among image blocks, which often leads to a locally optimal parameter selection, especially for SC. In this paper, we present a weighted RDO scheme for SC coding (SCC), in which the repeating characteristics are taken into account when deciding RD tradeoff for each block. For one block, the number being referenced by the current picture and following pictures is estimated and based on the number, we set a proper weight in the RDO process to reflect its importance from a global point of view. To estimate the number being referenced, we propose a hash-based method to approximate the results to avoid the complexity of direct search. Experimental results show that compared with the High Efficiency Video Coding SCC reference software, 10.1%, 14.5%, and 2.2% on average and up to 25.7%, 39.8%, and 4.6% bit saving can be achieved by considering weights provided by our scheme for hierarchical-B, IBBB, and all intra coding structures, respectively. Thanks to our hash-based design, the complexity increase brought by the proposed scheme is marginal.

Adaptive Color-Space Transform in HEVC Screen Content Coding

The screen content coding (SCC) Extensions of high efficiency video coding (HEVC) employs in-loop adaptive color-space transform (ACT) technique to explore the inter-color-component redundancy, i.e., statistical redundancy among different color components. In ACT, the prediction residual signal is adaptively converted into a different color space, i.e., YCgCo. The rate-distortion criteria is employed to decide whether to code the residual signal in the original color space or YCgCo color space. Typically, the inter-color-component correlation could be reduced when ACT is enabled. The residual signal after possible color-space conversion is then coded, following the existing HEVC framework, i.e., transform if necessary, quantization and entropy coded. This paper describes the design of ACT from several points of view, from theoretical analysis to implementation details. Experimental results are also provided to demonstrate the significant coding gains of ACT in the HEVC SCC Extensions.

Analysis of Screen Content Coding Based on HEVC

In this paper, the technical analysis and characteristics of screen content coding (SCC) based on High efficiency video coding (HEVC) are presented. For SCC, which is increasingly used these days, HEVC SCC standardization has been proceeded. Technologies such as intra block copy (IBC), palette coding, and adaptive color transform are developed and adopted to the HEVC SCC standard. This paper examines IBC and palette coding that significantly impacts RD performance of SCC for screen content. The HEVC SCC reference model (SCM) 4.0 was used to comparatively analyze the coding performance of HEVC SCC based on the HEVC range extension (RExt) model for screen content.

HEVC 스크린 콘텐츠 코딩 성능 향상을 위한 화면 내 블록 카피 기술 분석

This paper describes and analyzes IBC (intra block copy) in HEVC (high efficiency video coding) SCC (screen content coding) to improve the coding efficiency of IBC. HEVC SCC reference software SCM 2 is employed to analyze the selection ratio of IBC which is newly adopted in HEVC SCC, and the tools for IBC such as the block vector prediction and block vector coding method are evaluated. Experimental results show the average IBC selection ratio is 31.08% and 0.33% in I-Slice and B-Slice, respectively. Based on this results, the coding efficiency of IBC could be improved by utilizing IBC selectively. In addition, analysis tests of block vector prediction and the block vector coding method show the current methods are not efficient to screen content videos, and the analysis results are presented to improve these methods.

Early Termination of Block Vector Search for Fast Encoding of HEVC Screen Content Coding

This paper proposes an early termination method of a block vector search for fast encoding of high efficiency video coding (HEVC) screen content coding (SCC). In the proposed algorithm, two blocks indicated by two block vector predictors (BVPs) were first employed as an intra block copy (IBC) search. If the sum of absolute difference (SAD) value of the block is less than a threshold defined empirically, an IBC BV search is terminated early. The initial threshold for early termination is derived by statistical analysis and it can be modified adaptively based on a quantization parameter (QP). The proposed algorithm is evaluated on SCM-2.0 under all intra (AI) coding configurations. Experimental results show that the proposed algorithm reduces IBC BV search time by 29.23% on average while the average BD-rate loss is 0.41% under the HEVC SCC common test conditions (CTC).

Improved entropy coding for quantized transform coefficients in HEVC screen content coding

In the emerging high efficiency video coding (HEVC) standard, a Golomb-Rice code is adopted to binarize level information. The Golomb-Rice code is optimal for encoding symbols with the exponential probability distribution. In general, quantized transform coefficients of natural images show the exponential probability distribution. However, screen contents usually have a totally different probability distribution, and the Golomb-Rice code is not appropriate for screen content coding. In this paper, we focus on a new entropy coding scheme for screen content coding. In the proposed scheme, we clip inefficient high magnitude coefficient levels that do not fit the exponential probability distribution. Then, we apply a limited length Golomb-Rice code to binarize clipped levels. From experimental results, it is verified that the proposed method achieves on average 0.60 % BD-rate saving and up to 1.13 % BD-rate saving, compared to HEVC screen content coding. When the proposed method is combined with a well-known screen content coding technique, transform skipping, it shows up to 24.02 % BD-rate saving.