Fast and memory efficient JBIG2 encoder

We propose a fast and memory efficient encoding strategy for text image compression with the JBIG2 standard. The encoder splits up the input image into horizontal stripes and encodes one stripe at a time. Construction of the current dictionary is based on updating dictionaries from previous stripes. We describe separate updating processes for the singleton exclusion dictionary and for the modified-class dictionary. Experiments show that, for both dictionaries, splitting the page into two stripes can save 30% of encoding time and 40% of physical memory with a small loss of about 1.5% in compression. Further gains can be obtained by using more stripes but with diminishing returns. The same updating processes are also applied to compressing multi-page document images and shown to improve compression by 8-10% over coding a multi-page document as a collection of single-page documents.