JPS6419865A - Image reading device - Google Patents

Abstract

PURPOSE:To shorten a processing time by obtaining a correcting wave shape to be the reference of the shading correction for an original reading output, from an output wave shape to read the surface of a reading roller to carry an original and a reading wave shape of a reading starting edge. CONSTITUTION:The output ratio 1:r of a reference board 32 and a roller 39 of respective picture elements when the white reference board 32 and the reading roller 39 are read under the same condition is set in advance as a constant. A sensor unit 33 moves to a B position, and a sensor 34 reads the roller 39 before an original head edge achieves a writing position. When this wave shape is multiplied by the 1/r, that is coincident with a wave shape to read the reference board 32. The reading output wave shape of the roller 39 is stored as a shading wave shape and from a time point when the original head edge achieves the reading position, the image of the interval until a termination passes through the reading position is read. After the reading of one page is ended, the roller 39 is read while the next page achieves the reading position and the shading wave shape can be updated every page. Thus, the updated result can follow the elapsed change of the brightness of a light source 36.