Prediction image generation apparatus, video decoding apparatus, video coding apparatus, and prediction image generation method

A video decoding apparatus for decoding encoded data, the video decoding apparatus comprising:

• a CCLM prediction parameter derivation circuitry that derives (i) a first Cross-Component Linear Model (CCLM) prediction parameter and (ii) a second Cross-Component Linear Model (CCLM) prediction parameter;
• and
• a CCLM prediction filter circuitry that derives the prediction image by using (i) the first CCLM prediction parameter, (ii) the second CCLM prediction parameter, and (iii) a first shift value,
• wherein
• the first CCLM prediction parameter is derived by using (i) a first variable, (ii) a second shift value, and (iii) a right shift operation, wherein the first variable is a sum of a second variable and a value of a rounding parameter, wherein the second variable is a product of (a) a chroma difference value between a first chrominance sample value and a second chrominance sample value and (b) a value in a reference table defined by using an index,
• the index is derived based on (i) a luma difference value between a first luminance sample value and a second luminance sample value and (ii) a third shift value, wherein the third shift value is derived by using a logarithmic value based on the luma difference value,
• the second shift value is derived by adding one to a logarithmic value of an absolute value based on the chroma difference value, and
• the first shift value is derived by using the third shift value minus the second shift value.

A video encoding apparatus for encoding a video image, the video encoding apparatus comprising:

• a CCLM prediction parameter derivation circuitry that derives (i) a first Cross-Component Linear Model (CCLM) prediction parameter and (ii) a second Cross-Component Linear Model (CCLM) prediction parameter;
• and
• a CCLM prediction filter circuitry that derives the prediction image by using (i) the first CCLM prediction parameter, (ii) the second CCLM prediction parameter, and (iii) a first shift value,
• wherein
• the first CCLM prediction parameter is derived by using (i) a first variable, (ii) a second shift value, and (iii) a right shift operation, wherein the first variable is a sum of a second variable and a value of a rounding parameter, wherein the second variable is a product of (a) a chroma difference value between a first chrominance sample value and a second chrominance sample value and (b) a value in a reference table defined by using an index,
• the index is derived based on (i) a luma difference value between a first luminance sample value and a second luminance sample value and (ii) a third shift value, wherein the third shift value is derived by using a logarithmic value based on the luma difference value,
• the second shift value is derived by adding one to a logarithmic value of an absolute value based on the chroma difference value, and
• the first shift value is derived by using the third shift value minus the second shift value.