Image decoding apparatus and image coding apparatus

An image decoding apparatus for dividing a picture into multiple coding tree unit (CTU) rows and decoding each of the multiple CTU rows sequentially from top based on Wavefront Parallel Processing (WPP), the image decoding apparatus comprising:

• a prediction parameter decoding circuit configured to determine whether or not neighboring blocks are available for a target block included in a target CTU and, in a case that the neighboring blocks are available, derive a prediction parameter of the target block by referring the neighboring blocks;
• a prediction image generation circuit configured to generate a prediction image of the target block;
• and
• an entropy decoding circuit configured to initialize a context-adaptive binary arithmetic coding (CABAC) state at a start of a first CTU row including the target CTU and decode the target CTU, wherein
• the prediction parameter decoding circuit, in a case that the prediction parameter decoding circuit refers the neighboring blocks included in a second CTU row immediately above the first CTU row, derives the prediction parameter of the target block by using neighboring blocks included in a CTU up to a position being, in the second CTU row, located at a same position of the target CTU, and
• the entropy decoding circuit, in a case that the target CTU is located at a beginning position in the first CTU row, initializes the CABAC state of the target CTU by using a CABAC state of the CTU located at the same position of the target CTU in the second CTU row.