METHOD OF DISCRIMINATING DIFFERENT KINDS OF IMAGE AREAS, INVOLVING TWO-DIMENSIONAL ORTHOGONAL TRANSFORMS

摘要

An image area discriminating method surely distinguishes a character image area and a halftone image area printed on a single document in response to image data outputted by an image reader. An image of interest is divided into NxN blocks and subjected to two-dimensional orthogonal transform block by block to produce an NxN coefficient pattern. The blocks each is compared with coefficient patterns prepared beforehand and matching the characteristics of character images to see if the block lies in a character image area or in a halftone image area. The NxN coefficients may be replaced with NxN vectors. Then, a necessary number of vectors are selected out of the NxN vectors to generate a upsilon -dimensional coefficient vector, and it is compared with vecotrs prepared beforehand for character identification and matching the characteristics of character images.