Low complexity transform coding using adaptive dct/dst for intra-prediction

An apparatus for decoding video, comprising:

• an inverse quantizer configured to map quantized transformed coefficient indices obtained from an incoming video bitstream to an M×N transformed coefficient matrix according to an intra-prediction mode of the incoming video bitstream;
• and
• an inverse transform unit configured to determine to apply a first one of discrete cosine transform (DCT) and discrete sine transform (DST) as an inverse vertical transform and a second one of DCT and DST as an inverse horizontal transform for the transformed coefficient matrix according to the intra-prediction mode, and perform an inverse transform comprising the inverse vertical transform and the inverse horizontal transform, using the first one of DCT and DST for the inverse vertical transform and the second one of DCT and DST for the inverse horizontal transform to calculate an approximation of an error prediction residual.

An apparatus for encoding video, comprising:

• a unified intra-prediction unit configured to perform intra-prediction on an input matrix of an M×N input image block (X) based on an intra-prediction mode to generate {tilde over (X)} and obtain an M×N intra-prediction residue matrix (E);
• and
• a transform unit configured to determine to apply a first one of discrete cosine transform (DCT) and discrete sine transform (DST) as a horizontal transform and a second one of DCT and DST as a vertical transform for E according to the intra-prediction mode, and perform a forward transform comprising the horizontal transform and the vertical transform, using the first one of DCT and DST as the horizontal transform and the second one of DCT and DST for the vertical transform to calculate a transformed coefficient matrix (E2).