Abstract: An enhancement to the standard JPEG image data compression technique includes a step of recording the length of each string of bits corresponding to each block of pixels in the original image at the time of compression. The list of lengths of each string of bits in the compressed image data is retained as an "encoding cost map" or ECM. The ECM, which is considerably smaller than the compressed image data, can be transmitted or retained in memory separate from the compressed image data along with some other accompanying information and is used as a "key" for editing or segmentation of the compressed image data.

Abstract: A universal halftone image unscreening method includes: 1) decomposing the halftone image into a plurality of subband image levels, where each subband image level includes a plurality of subband images; 2) selectively filtering the plurality of subband images of each subband image level; and 3) recomposing the plurality of filtered subband images into a continuous tone image. The continuous tone image can then be further filtered to enhance its appearance. The subband images are preferably formed using the discrete wavelet transform, but can be formed using any known transform. The subband images are selectively filtered using a non-edge areas noise attenuating filter and a plurality of oriented filters. The halftone image is preferably decomposed using an N-stage halftone image decomposer, wherein each of the N decomposer stages comprises a set of low-pass and high-pass filters.

Abstract: A method of fast decompressing a document image compressed using transform coding for scaling and previewing purposes. A fast algorithm is derived by utilizing a fraction of all available transform coefficients representing the image. The method is particularly efficient using the discrete cosine transform which is used in the JPEG ADCT algorithm. In JPEG ADCT, a very fast and efficient implementation is derived for a resolution reduction factor of 16 to 1 (4 to 1 in each direction) without needing any floating point arithmetic operations.