Image decoding device and image decoding method

Abstract

The present invention avoids waste caused by performing both a Secondary Transform and an Adaptive Multiple Core Transform. Provided is a device including: a core transform unit (1521) that can perform an Adaptive Multiple Core Transform on a Coding Tree Unit; and a Secondary Transform unit (1522) that can perform, before the Adaptive Multiple Core Transform, a Secondary Transform on at least any one of sub-blocks included in the Coding Tree Unit. The device omits any of the Adaptive Multiple Core Transform and the Secondary Transform in accordance with at least any of a flag associated with the Adaptive Multiple Core Transform and a flag associated with the Secondary Transform, or in accordance with a size of the Coding Tree Unit.

1 . An image decoding device configured to decode a picture by using a coding unit into which the picture is split, the device comprising:
 a first decoding circuit configured to decode a secondary index, wherein the secondary index equal to 0 specifies that a secondary transform is not used;   a second decoding circuit configured to decode a first index;   a first transform circuit configured to apply the secondary transform based on the secondary index; and   a second transform circuit configured to apply a core transform based on the first index,   wherein the first decoding circuit decodes the secondary index based on a coding mode being an intra prediction mode and a number of non-zero coefficients,   the second decoding circuit derives the first index equal to 0 based on the secondary index not equal to 0,   the first transform circuit
 rearranges a two-dimensional transform coefficient, corresponding to a transform unit included in the coding unit, in a one-dimensional array, 
 derives a transform matrix based on the secondary index, and 
 applies the secondary transform by using the transform matrix and the one-dimensional array. 
   
     
     
         2 . An image decoding method for decoding a picture by using a coding unit into which the picture is split, the method comprising:
 decoding a secondary index based on a coding mode being an intra prediction mode and a number of non-zero coefficients, wherein the secondary index equal to 0 specifies that a secondary transform is not used;   decoding a first index;   deriving a transform matrix based on the secondary index;   rearranging a two-dimensional transform coefficient, corresponding to a transform unit included in the coding unit, in a one-dimensional array;   applying the secondary transform by using the transform matrix and the one-dimensional array;   applying a core transform based on the first index, wherein the first index is derived equal to 0 based on the secondary index not equal to 0.