Image reading apparatus and binary conversion process therefor.

摘要

An image reading apparatus comprises a white plate (1a) for obtaining a reference signal, a line image sensor (5) for scanning an original, a central processing unit (11) for evaluating the proportion of the density of an original for every cell of an image sensor based on the reference voltage signal from the white plate (1a) and the output signal obtained from the original (1), and for evaluating a threshold value for binary converting the image of the original based on the distribution of the density proportion, whereby the image portion of the original is extracted based on the threshold value.