Image coding apparatus and image decoding apparatus

An image coding apparatus for coding an input image, the image coding apparatus comprising a loop filter circuitry configured to:

• generate a luminance image by a process of scaling a luminance pixel value by using a histogram of decoded luminance, a process of a low-pass filter to a boundary of prediction unit or a transform unit so as to smooth pixels around the boundary and a process of categorizing pixels for the luminance image and a process of adding an offset according to a categorization;
• apply an adaptive loop filter to the luminance image and a chrominance image, and output a filtered luminance image and a filtered chrominance image;
• derive an added value by using an equation (sum+64)>>7, wherein the sum is product sum of the luminance image and a cross component filter coefficient;
• derive a clipped value by clipping the added value within a range based on a bit depth;
• and
• derive a modified filtered chrominance image by adding the clipped value to the filtered chrominance image.

An image decoding method for decoding an input image, generating a decoded image and filtering the decoded image, the image decoding method comprising

• generating a luminance image by a process of scaling a luminance pixel value by using a histogram of decoded luminance, a process of a low-pass filter to a boundary of prediction unit or a transform unit so as to smooth pixels around the boundary and a process of categorizing pixels for the luminance image and a process of adding an offset according to a categorization;
• applying an adaptive loop filter to the luminance image and a chrominance image, and output a filtered luminance image and a filtered chrominance image;
• deriving an added value by using an equation (sum+64)>>7, wherein the sum is product sum of the luminance image and a cross component filter coefficient;
• deriving a clipped value by clipping the added value within a range based on a bit depth;
• and
• deriving a modified filtered chrominance image by adding the clipped value to the filtered chrominance image.