Lossless/Lossy Compression of Bi-level Images

We present a general and robust method for lossless/lossy coding of bi-level images. The compression and decompression method is analoguous to JBIG, the current international standard for bi-level image compression, andis based on arithmetic coding and a template to determine the coding state. Loss is introduced in a preprocess on the encoding side by flipping pixels in a controlled manner.

The method is primarily aimed at halftoned images as a supplement to the specialized soft pattern matching techniques which work better for text. The new algorithm also works well on documents of mixed contents e.g. halftoning and text without any segmentation of the image. The decoding is analoguous to the decoder of JBIG which means that software implementations easily have a through-put of 1 Mpixels per second.In general, the flipping method can target the lossy image for a given not-too-large distortion ornot-too-low rate.

The current flipping algorithm is intended for relatively fast encoding and moderate latency.By this method, many halftones can be compressed at perceptually lossless quality at a rate whichis half of what can be achieved with (lossless) JBIG.The (de)coding method is proposed as part of JBIG-2, an emerging international standard for lossless/lossy compression of bi-level images.