Image rendering for digital fax

Conventional halftoning methods such as error diffusion and ordered dithering are poorly suited to the compression of halftone images using the baseline fax compression schemes CCITT G3 and G4. This paper proposes an efficient and flexible solution for binary representation of mixed content documents using CCITT G3/G4 compression. The solution includes two variations which we refer to as FastFax and ReadableFax. FastFax performs edge detection and text detection by applying locally adaptive binary thresholding and combines the two detection results together. The FastFax algorithm produces an accurate representation of binary mixed document content with high compressibility using CCITT G3/G4 compression. ReadableFax is based on FastFax and applies clustered dot screening to background and halftone regions to enhance graphic content. Both methods provide accurate representation of image content while allowing for substantial compressibility, and provides a tradeoff between representation quality and bitrate.