Patent Document ID: 5426512
Application ID: 08186366
Patent Status: 1

Claim One:
1. The method for transforming a block having an index k of pixels from an electronic image into a digital representation of said image comprising the steps of: (a) applying a Discrete Cosine Transform (DCT) to transform said block of pixels into digital signals represented by DCT transformation coefficients C.sub.ijk); (b) selecting a DCT mask (m.sub.ijk) for each block of pixels based on parameters comprising said DCT transformation coefficients C.sub.ijk and display and perceptual parameters; (c) selecting quantization matrix (g.sub.ij) comprising the steps of: (i) selecting an initial value of q.sub.ij having a DCT coefficient C.sub.ijk ; (ii) quantizing each DCT coefficient ci.sub.ijk in each block k to form quantized coefficient U.sub.ijk ; (iii) de-quantizing the quantized coefficients u.sub.ijk by multiplying them by q.sub.ij to form q.sub.ij u.sub.ijk ; (iV) subtracting the de-quantized coefficient q.sub.ij u.sub.ijk from c.sub.ijk to compute a quantization error e.sub.ijk ; (v) dividing e.sub.ijk by the DCT mask m.sub.ijk to obtain perceptual errors; (vi) pooling the perceptual errors of one frequency .sub.ij over all blocks k to obtain an entry in a perceptual error matrix p.sub.ij ; (vii) repeating steps i-vi for each frequency .sub.ij ; (viii) adjusting the values q.sub.ij up or down until each entry in the perceptual error matrix p.sub.ij is within a target range; and (ix) entropy coding said quantization matrix and the quantized DCT coefficients of said image.