Abstract
In hybrid block-based video coding, transform plays an important role in energy compaction. Transform coding converts residual data in the spatial domain into frequency domain data, thereby concentrating energy in a lower frequency band. In VVC (versatile video coding), the primary transform is performed using DCT-II (discrete cosine transform type 2), DST-VII (discrete sine transform type 7), and DCT-VIII (discrete cosine transform type 8). Considering that DCT-II, DST-VII, and DCT-VIII are all linear transforms, inverse transform is proposed to reduce the number of computations by using the linearity of transform. When the proposed inverse transform using linearity is applied to the VVC encoder and decoder, run-time savings can be achieved without decreasing the coding performance relative to the VVC decoder. It is shown that, under VVC common-test conditions (CTC), average decoding time savings values of 4% and 10% are achieved for all intra (AI) and random access (RA) configurations, respectively.
Highlights
IntroductionTransform coding is an important part of video coding, and it has been successfully adopted in most video coding standards, including Moving Picture Experts Group (MPEG)-4 AVC (advanced video coding)/H.264 [1,2], HEVC (high efficiency video coding)/H.265 [3,4], and VVC/H.266 [5,6]
Transform coding is an important part of video coding, and it has been successfully adopted in most video coding standards, including Moving Picture Experts Group (MPEG)-4 AVC/H.264 [1,2], HEVC/H.265 [3,4], and VVC/H.266 [5,6]
In hybrid block-based video coding, a transform is applied to the residual signal obtained after intra/inter-prediction, and the residual signals in the spatial domain are converted into the frequency domain
Summary
Transform coding is an important part of video coding, and it has been successfully adopted in most video coding standards, including MPEG-4 AVC (advanced video coding)/H.264 [1,2], HEVC (high efficiency video coding)/H.265 [3,4], and VVC/H.266 [5,6]. It is well known that the Karhunen–Loève transform (KLT) [7] is the optimal transform in terms of data decorrelation and compaction. Because of the diverse characteristics of images and videos, DCT-II is not always an optimal transform in terms of energy compaction and decorrelation. To solve this problem, alternative transform schemes such as DCT-II/DSTVIII for video coding [9] and enhanced multiple transform (EMT) [10] have been proposed. HEVC specified the core transform based on DCT-II for the 4 × 4, 8 × 8, 16 × 16, and 32 × 32 predicted residual blocks and an alternate transform based on DST-VII for the 4 × 4 intra-predicted residual block [12]
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