Separable subsampling of digital image data with general periodic symmetry

A method of subsampling a digital color image to decompose said image data into general periodic spatial frequency regions comprising the steps of:

• converting the input color image data into a chosen color space using a color transformation;
• unsampling said image by inserting pixel values of zero in the transformed data obtained in the previous step to modify the rectangular symmetry of the input color image data into a preferred symmetry;
• processing the upsampled image data using one-dimensional low-pass and high-pass filters and subsampling all of the color image data including the inserted pixel values at a first angle so as to be aligned with the periodicity of the upsampled image;
• and
• processing the resultant subsampled image data using one-dimensional low-pass and high-pass filters and subsampling all of the data remaining after the previous step at a second angle orthogonal to said first angle.