Mixed content image compression by gradient field integration

Sketch based image coding decomposes an input image into a piece-wise smooth approximation image and a residual image. Image compression by gradient field integration follows this model, but differs by generating the approximation image from gradient data along edge contours and regularly sampled low resolution image data. This allows direct and efficient calculation of an approximation image which is smooth between edges. In this paper, we describe the image compression by gradient field integration approach, together with a low complexity implementation intended for near visually lossless compression of mixed content images. The implementation uses gradient field integration by scanline convolution, simple edge data extraction, DCT residual image coding and is block-based; it is suited to compression of images containing sharp edges occurring along pixel borders. Compression results are provided indicating potential gains from this method.