Adaptively subsampled image coding with warped polynomials
This paper presents an adaptive image coding method which uses an image dependent orthogonal transform. The method is a generalization of a one-dimensional coding scheme which represents signals as linear combinations of signal-dependent time-warped (TW) orthogonal polynomials. This paper briefly summarizes the theory of time-warped signal coding; next, it describes the new image compression method. Basically, this method transforms all of the image rows and columns with different, but not completely independent bases. By adapting the bases to the image, high quality coding is achieved even when retaining only a small number of transform coefficients. Also, the overhead involved in coding the bases is very small. This paper shows that at net bit rates of about 0.3 bpp, images compressed by the new method are sharper and less distorted by ringing effects than those produced by JPEG or the full-image DCT. Block distortion, which is an important problem in JPEG at 0.3 bpp cannot occur in the new method, since it transforms the full image instead of blocks.<<ETX>>