Optimal intra prediction in block-based video coding to calculate minimal activity direction based on texture gradient distribution
View Patent ↗Simplified selection of optimal intra prediction in block-based video coding based on texture gradient distribution and minimal activity direction. The minimal activity direction is defined by a vector (α(B, W), β(B, W)) indicating minimal variation of a discrete function P(x, y) inside a spatial aria of block B with weights W.
1. A video codec comprising a control circuit configured and arranged to calculate minimal activity direction based on texture gradient distribution, the minimal activity direction being defined by a vector (α(B, W), β(B, W)) indicating minimal variation of a discrete function P(x, y) inside a spatial area of block B with weights W; the vector (α(B, W), β(B, W)) being a solution of a minimization problem:
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wherein
α 2 +β 2 =1;
P(x, y) is a discrete function defined at a rectangular set of integer pairs:
R= {0,N−1} × {0,M−1} in N×M frame;
S is a set of integer coordinate pairs (x, y), where S ⊂ R;
W(x, y) is a set of non-negative weight coefficients defined at a point (x, y)εS;
D x (x, y) and D y (x, y) are measures of function P(x, y) variations in the neighborhood of the (x, y) point:
D X ( x,y )=( P ( x+ 1, y )− P ( x− 1, y ))/2; and
D Y ( x,y )=( P ( x,y+ 1)− P ( x,y− 1))/2;
wherein
Σ W ( x,y )· D X 2 ( x,y )+Σ W ( x,y )· D Y 2 ( x,y )≠0.
2. A video codec of claim 1 , wherein the control circuit further configured and arranged to provide simplified selection of an optimal intra prediction by:
choosing a texture block B of size L×L starting with coordinates (x, y);
choosing a spatial area S including the texture block B;
choosing a weight matrix for S, wherein in a simplest case all weights w(j, k)=1;
calculating the minimal activity direction (α, β) and a corresponding angular intra prediction mode;
defining a set Q of intra predictions for selecting an optimal intra prediction mode P k , the set Q including at least a plurality of angular intra predictions for angles γ 0 , γ 1 . . . γ T−1 , and a plurality of non-angular intra predictions;
calculating minimal activity direction strengths for the block B with weights W;
constructing a reduced set of intra predictions Q 1 by excluding from the set Q at least one plurality of intra predictions; and
selecting the optimal intra prediction P k from the reduced set Q 1 of intra predictions.
3. The video codec of claim 2 , wherein the control circuit further configured and arranged to calculate the minimal activity direction strengths for block B with weights W:
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4. The video codec of claim 3 , wherein the control circuit is further configured and arranged to construct the reduced set of intra predictions Q 1 by excluding at least one plurality of intra predictions from the set Q based on the following:
if C 1 ({tilde over (B)},W)<X 1 , excluding the plurality of angular intra predictions for the angles γ 0 , γ 1 . . . γ T−1 ;
if C 1 ({tilde over (B)},W)>X 2 and C 2 ({tilde over (B)},W)<X 3 excluding the plurality of non-angular predictions;
wherein X 1 , X 2 , X 3 are constants for parameters defined by desired speed and quality of encoding.