Cross-component linear model prediction image generation apparatus, video decoding apparatus, video coding apparatus, and prediction image generation method
The amount of memory required for CCLM prediction is reduced. The CCLM prediction parameter derivation unit ( 310442 ) derives a scale shift value corresponding to a luma difference value, and derives a CCLM prediction parameter, by shifting, by using the scale shift value, a value obtained by multiplying a value of a table referred to with a value obtained by performing right shift of the luma difference value by the scale shift value as an index and a chroma difference value. In addition, in a case of deriving a prediction image, a bit width is reduced by adaptively deriving a shift amount of a linear prediction parameter from the chroma difference value.
1. A prediction image generation apparatus for generating a prediction image by using an intra prediction parameter including a Cross-Component Linear Model (CCLM) prediction mode, the prediction image generation apparatus comprising:
CCLM prediction parameter circuitry that derives:
(i) a first difference value, which is a difference between chrominance values,
(ii) a first variable by using (a) a second difference value, which is a difference between luminance values, (b) a first logarithmic value derived by using the second difference value, and (c) a right shift operation,
(iii) a shift value by using a second logarithmic value derived by using an absolute value of the first difference value, and
(iv) a CCLM prediction parameter by using (a) the first variable, (b) the first difference value, and (c) the shift value; and
a CCLM prediction filter that derives the prediction image by using the CCLM prediction parameter,
wherein
the CCLM prediction parameter is derived by right shifting a second variable by the shift value, wherein the second variable is a sum of a third variable and a value of a rounding parameter, wherein the third variable is a product of (i) the first difference value and (ii) a value, in a reference table, defined by using the first variable.
2. The prediction image generation apparatus of claim 1 , wherein a first value and a last value in the reference table is equal to 0.
3. A video decoding apparatus configured to decode an image by adding a prediction image generated from the CCLM prediction filter according to claim 1 and a residual.
4. A video coding apparatus configured to code a residual from a difference between a prediction image derived from the CCLM prediction filter according to claim 1 and an input image.
5. A prediction image generation method for generating a prediction image by using an intra prediction parameter including a Cross-Component Linear Model (CCLM) prediction mode, the prediction image generation method including:
deriving a first difference value, which is a difference between chrominance values,
deriving a first variable by using (i) a second difference value, which is a difference between luminance values, (ii) a first logarithmic value derived by using the second difference value, and (iii) a right shift operation,
deriving a shift value by using a second logarithmic value derived by using an absolute value of the first difference value, and
deriving a CCLM prediction parameter by right shifting a second variable by the shift value, wherein the second variable is a sum of a third variable and a value of a rounding parameter, wherein the third variable is a product of (i) the first difference value and (ii) a value, in a reference table, defined by using the first variable; and
deriving the prediction image by using the CCLM prediction parameter.