PURPOSE: To read an optical character recognition device when multistage gray scale information is printed on a document which is not white and a document having a background with noises by using a specific video image processor.

CONSTITUTION: A video image processor 10 generates the histogram of the gray scale pixel value of image data for each type of a document by a histogram generating circuit 12, and detects the peak of black and the reference of white by a black peak and white reference detecting circuit 16. A background percentage level can be exactly prevented from being too dark by measuring a print contrast rate by a print contrast rate measuring and normalized coefficient circuit 20. Next, a picture element which is brighter than the background level is turned white, and the black picture element is turned supreme black by using a normalized coefficient by an image normalizing circuit 22, and a single pixel spot or the like is removed through an image correlator 24 by an image filter 26.