Improved SAP based on adaptive directional prediction for HEVC lossless intra prediction

On lossless intra coding in HEVC with 3-tap filters

“…However, since the transform is skipped in lossless coding, a pixel-by-pixel spatial prediction approach can now be used instead of a block-based approach for more efficient prediction. Many lossless intra coding methods based on pixel-by-pixel prediction approach appeared in the literature [8,9,10,11]. One such method applied in HEVC is provided in [8] and is called Sample-based Angular Prediction (SAP).…”

“…A more recent pixel-by-pixel prediction approach is given in [11], and is called adaptive directional SAP (AD-SAP). This method is similar to the SAP method discussed above, in the sense that the same prediction equations are used in a pixel-bypixel manner.…”

“…In the first group of approaches, first the block-based intra prediction is performed and then the prediction error block is further processed with a second pixel-by-pixel prediction step [3,4,5,6,7]. In the second group of approaches, the block-based prediction approach is replaced directly with a pixel-by-pixel prediction approach [8,9,10,11]. These approaches are discussed in more detail in the next section.…”

Lossless intra coding in HEVC with adaptive 3-tap filters

“…Figure 1 is an example of the projection of a pixel in SAP and HEVC. Similar algorithm to SAP is adaptive directional SAP (AD-SAP) [9]. In this approach the prediction is similar SAP [8] but encoder may change the direction of the prediction if it can remove the spatial redundancy more efficient than the ordinary SAP.…”

“…In the first set [3], [4], [5], [6], [7], the residual block is post processed such that its energy is lowered. In the second set of approaches [8], [9], [10], [11], [12], the prediction is obtained by using pixel-by-pixel spatial prediction instead of block-based prediction. The details of the spatial prediction methods based on pixel-by-pixel predictions will be discussed in the following section.…”