A system and method for classifying an image block of a printed image into
contone, halftone, or error diffusion classes, includes scanning the
printed image; selecting an n by n block of pixels from the scanned image
in a luminance channel; calculating an array of DCT coefficients of the
pixel block, wherein the calculated DCT coefficients are representative
of spatial frequency and spatial orientation of the pixel block;
comparing the array of DCT coefficients with an array of predetermined
values, wherein the array of predetermined values are indicative of
contone, halftone and error diffusion classes; and determining the image
classification of the pixel block based on the comparison of the DCT
coefficients with the array of predetermined values. If the image is
determined to be halftone, then the method further evaluates the DCT
coefficients to determine the frequency of the halftone screen.