Many images, including digital documents, are based on lines. If the lines of a digital document are extracted, the amount of space necessary to store the line information is much smaller than the space necessary to store the pixel information. Digital scans of physical documents, however, are usually less than perfect.
Noise is usually present, and gaps in the salient lines can appear.
Once the lines have been extracted, they may be approximated by Bezier curves or straight line segments and then stored in this compact form. In addition to the above compression research, we have compared existing technologies for the compression of bi-tonal and grayscale images. JBIG allows hierarchical encoding of bi-tonal images, and encodes the images in horizontal regions called stripes. By applying the JBIG algorithm to multiple bit planes of grayscale images, we will be able to preserve the grayscale information that is important for browsing some images. In order to allow random access to parts of the image interactively requested by the user, we encode the image with an explicit reset of the arithmetic encoder state probability status for contexts after each stripe, and we keep track of where the data for each stripe is found within the encoded data for the entire image.