Image decoding apparatus and image coding apparatus for scaling transform coefficient

An image encoding apparatus for scaling a transform coefficient for a luminance component, the image encoding apparatus comprising:

• a scaling list encoder configured to encode a flag specifying whether a scaling matrix is applied in a case that a non-separable transform is applied;
• scaling circuitry configured to scale the transform coefficient by using a scaling list which is set to a predetermined value or set to the scaling matrix;
• and
• a transform unit (TU) encoder configured to encode a non-separable transform index specifying whether non-separable transform is used, wherein
• the scaling circuitry is further configured to set a value of a non-separable transform variable equal to one in a case that a value of the non-separable transform index is not equal to zero;
• and
• the scaling circuitry is further configured to set the predetermined value to the scaling list in a case that a value of the flag is equal to one and the value of the non-separable transform variable is equal to one.

An image decoding method for scaling a transform coefficient for a luminance component, the image decoding method comprising:

• decoding a flag specifying whether a scaling matrix is applied in a case that a non-separable transform is applied;
• scaling the transform coefficient by using a scaling list which is set to a predetermined value or set to the scaling matrix;
• and
• decoding a non-separable transform index specifying whether the non-separable transform is used, wherein
• a value of a non-separable transform variable is set equal to one in a case that a value of the non-separable transform index is not equal to zero;
• and
• the predetermined value is set to the scaling list in a case that a value of the flag is equal to one and the value of the non-separable transform variable is equal to one.