Apparatus, a method and a computer program for video coding and decoding

A method comprising:

• receiving an image block unit of a frame, the image block unit comprising a plurality of samples in color channels comprising at least one chrominance channel and a luminance channel;
• reconstructing samples of said luminance channel of the image block unit;
• determining a reference area for predicting target samples of at least one color channel of the image block unit, wherein said reference area comprises one or more reference samples in a neighboring block in one or more of following:
• a current color channel or frame, in the neighboring of a co-located block in a reference color channel or frame;
• or the co-located block in the reference color channel or frame;
• determining weights for predicting said target samples based on a ratio between a normalized luminance histogram in said reference area and a normalized luminance histogram co-locating said target samples;
• determining filter coefficients of a filter for said predicting based on the weights, the one or more reference samples and a shape of the filter;
• and
• predicting samples of the at least one color channel of the image block unit based on the samples of said luminance channel and the filter coefficients.

A computer program product comprising a non-transitory computer readable storage medium having program code portions stored thereon, the program code portions configured, upon execution, to:

• receiving an image block unit of a frame, the image block unit comprising a plurality of samples in color channels comprising at least one chrominance channel and a luminance channel;
• reconstruct samples of said luminance channel of the image block unit;
• determine a reference area for predicting target samples of at least one color channel of the image block unit, wherein said reference area comprises one or more reference samples in a neighboring block in one or more of following:
• a current color channel or frame, in the neighboring of a co-located block in a reference color channel or frame;
• or the co-located block in the reference color channel or frame;
• determining weights for predicting said target samples based on a ratio between a normalized luminance histogram in said reference area and a normalized luminance histogram co-locating said target samples;
• determine filter coefficients of a filter for said predicting based on the weights, the one or more reference samples and a shape of the filter;
• and
• predict samples of the at least one color channel of the image block unit based on the samples of said luminance channel and the filter coefficients.