Image coding apparatus and image decoding apparatus

Abstract

In a case that luminance information is used for a chrominance prediction in a separate coding tree structure, there is a problem that chrominance blocks cannot be decoded before all luminance blocks constituting a tree are decoded. An image decoding apparatus that splits an image into coding tree units (CTUs) that are rectangular for processing includes a CT information decoding unit configured to split a CTU of the CTUs into coding trees CTs and to process one or more color components as a single coding tree using one coding tree CT of the coding trees CTs or process two or more color components as a separate coding tree using two or more coding trees CTs of the coding trees CTs depending on a tree mode, a CU decoding unit configured to decode a split flag indicating whether to further split a CT of the CTs and to recursively perform block splitting, and an intra predictor configured to use a decoded image of one color component to generate a prediction image of another color component. The CU decoding unit does not decode the split flag from coded data but configures 1 in the split flag in a case of an intra slice, the separate coding tree, and a target CT size being larger than a prescribed maximum intra size.

1 - 15 . (canceled) 
     
     
         16 . An image decoding apparatus that splits an image into coding tree units (CTUs) that are rectangular for processing, the image decoding apparatus comprising:
 decoding a parameter indicating whether to use a single coding tree using one coding tree or a separate coding tree using two or more coding trees in the CTU;   in a case that separate coding tree is used in the CTU,
 reducing a target size and recursively performing block splitting by using the separate coding tree if a slice type is an intra slice, a value of the parameter indicates to use the separate coding tree, and the target size is greater than a prescribed maximum size; 
 decoding a split flag, from a coding data, indicating whether or not to further split a coding unit (CU) having the target size if the target size is less than or equal to the prescribed maximum size, and greater than a prescribed minimum size; and 
 splitting the CU by using the separate coding tree if a value of the split flag indicates to further split the CU. 
   
     
     
         17 . The image decoding apparatus according to  claim 16 , wherein
 the parameter is decoded when the image has two or more color components.