Image reader

Abstract

An image reader to detect a width size and a length size of a manuscript without moving an optical image read device. A front end detector inputs binary coded data of a shading line of a front end of the manuscript, counts a number of black pixels in a lengthways direction of the shading line, calculates a width size of the front end of the manuscript from a counted value, and outputs a front end detection signal for representing that the front end of the manuscript passes through an image read line. A rear end detector stores initial density information of a surface color of a white plate mounted over the optical image read device into an internal register, the initial density information being read in an initial operation, inputs the front end detection signal from the front end detector, starts a counting using an internal counter, continuously compares density information of the image of the manuscript, contained in a first gamma-corrected digital signal output from a gamma corrector in an image read operation, with the initial density information stored in the internal register every predetermined time, stops the counting when both pieces of the density information are coincident with each other, and calculates a length from the front end to the rear end of the manuscript from a counted value of the counter.