Image decoding apparatus and image coding apparatus that involves bi-prediction
A WP prediction and a GBI prediction are adaptively used in combination. A video decoding apparatus ( 31 ) includes: a weighted prediction unit ( 3094 ) configured to generate a prediction image by using at least one of a weight coefficient or an offset configured for a first unit region and a weight coefficient configured for a second unit region different from the first unit region, the weight coefficient and the offset each being applied to a pixel value included in one or a plurality of reference images.
1. An image decoding apparatus for performing image decoding processing with reference to a prediction image, the image decoding apparatus comprising:
a parameter decoding circuit configured to decode a reference picture indices refldxL0 and refldxL1 for each coding unit (CU) from coded data, and decode a plurality of weight information for each slice header from the coded data; and
a prediction image generation circuit configured to generate a bi-prediction image by using first weight coefficients of a first prediction or second weight coefficients of a second prediction,
wherein the prediction image generation circuit derives variables LumaWeightL0 and LumaWeightL1 based on the weight information, and derives the first weight coefficients of the first prediction equal to LumaWeightL0[refldxL0] and LumaWeightL1[refldxL1],
the prediction image generation circuit derives a Generalized bi-prediction index gbiIndex for each CU, derives a first one of the second weight coefficients of the second prediction equal to gbwTable[gbiIndex], and derives a second one of second weight coefficients based on the first one of the second weight coefficients, the gbiIndex indicates one of elements of the gbwTable, and the gbwTable is a table not decoded from the coded data,
in a case that the first prediction is on, the second prediction is on, and the Generalized bi-prediction index is equal to a predetermined value, the prediction image generation circuit generates the bi-prediction image by using the first weight coefficients of the first prediction, and
in a case that the first prediction is on, the second prediction is on, and the Generalized bi-prediction index is not equal to the predetermined value, the prediction image generation circuit generates the bi-prediction image by using the second weight coefficients of the second prediction.
2. The image decoding apparatus according to claim 1 , wherein the predetermined value is 0.
3. The image decoding apparatus according to claim 1 , wherein the elements of the table are {4,5,3,10,−2}.