An algorithm, which performs connected components detection in the course of decoding ITU-T (former CCITT) facsimile Group 3/4, i.e., MH/MR/MMR compressed images is presented. New definitions of mode color and a new transition element are introduced that allow MR/MMR codes to analyze and derive information about connection of black runs in two adjacent scan lines in the course of decoding. The experiments on the standard set of eight CCITT documents have shown that, on the average, the complexity of direct processing of MR/MMR codes is lower by a factor of 20 and 2.5 than that for raster images and MH codes processing respectively. Data structures for image vector description are discussed.

This paper presents a novel approach to document image compression that is efficient in both compression and processing flexibility. By proper exploitation of the structural characteristics of compressed data, one may obtain high performance for image operations with low complexity. Based on CCITT Group 4, an improved coding scheme (MG4), which exploits the 2-dimensional correlation between scan lines, is developed. Then such operations as skew detection, skew correction and connected component extraction are investigated and implemented. These operations are shown to run faster in the compressed domain than traditional methods.