METHOD OF CLASSIFYING A CHROMA DOWNSAMPLING ERROR

There is provided an apparatus and a method of evaluating an effect of chroma downsampling in a compression process of an input image. According to examples of the presently disclosed subject matter the method can include: computing an error for a target chroma downsampling (“CDS”) block based on characteristics of DCT coefficients in the U and/or V planes of a respective CDS candidates group in the input image, and further based on a diversity of the DCT coefficients in the U and/or V planes of the respective CDS candidates group in the input image; and computing an estimated perceptual effect of CDS over the input image based on a plurality of target CDS blocks error values.