Apparatus, a method and a computer program for video coding and decoding

Abstract

There is disclosed a method comprising obtaining a block of transform coefficients; searching a position of a last non-zero coefficient in a scan order in the block; selecting a secondary transform mode based on the position and encoding first syntax elements indicative of the selected secondary transform mode. A primary transform mode is selected based on the secondary transform mode. Second syntax elements indicative of the selected primary transform mode and third syntax elements defining the transform coefficients within the block are encoded. There is also disclosed a method comprising receiving encoded information related to a block of transform coefficients; decoding an indication of a position of a last non-zero coefficient in a scan order in the block and using the position to determine if an indication of a secondary transform mode is present in the bit stream. If so, first syntax elements indicative of the secondary transform mode are decoded and used to determine if an indication of a primary transform mode is present in the bit stream. If so, second syntax elements indicative of the primary transform mode are decoded. The transform coefficients are decoded and the determined transform modes are applied to select transforms and the transforms, if any, are applied to the transform coefficients.