Data compression for check processing machines
A technique of compressing image data derived from personal checks which possess several gray levels is described. Check images consist of both essential information such as printed and handwritten characters and nonessential background pattern or picture. Only the character plane is to be coded. Our proposed technique is divided into two phases: character plane extraction and character plane coding. In the first phase, a character plane which is composed of character pels on a uniform background is extracted from an original digital check image by using a combination of fundamental techniques of image segmentation. In the second phase, the extracted character plane is separated into a bit plane and a gray-level plane. The bit plane which preserves the position information of character pels on the character plane is conditional entropy coded. An adaptive two- or one-dimensional predictive coding scheme is applied to the gray-level plane which consists of only the character pels on the character plane. The check data are stored for further use as a combination of the codes derived from the bit plane encoder and the gray-level encoder in a check processing machine. A comparative study shows that the proposed coding scheme performs much better than conventional predictive coding schemes. For 8 gray-level image data, a compression factor of about 8:1 has been achieved.