Patent ID: 6295140
Filing Date: 2001-09-25
Classification: H04N

Abstract:
A document reading apparatus comprising:a white platen roller positioned at an image reading portion and used to provide white reference data used for shading correction for the document reading apparatus;an image sensor positioned in the image reading area and used to selectively read the white platen roller, and to output signal characteristic data after reading the white platen roller; anda controller configured to control the reading of the white platen roller so that the image sensor reads the white platen roller a predetermined number of times, and to control movement of the white platen roller such that a motor used to move the white platen roller is de-energized when the image sensor reads the white platen roller;wherein the controller receives the output signal characteristic data and compares the read output signal characteristic data to pre-existing signal characteristic data to determine if an abnormality exists in the read output signal characteristic data, such that when an abnormality is determined for read output signal characteristic data, the read output signal characteristic data is not used as white reference data; and such that when no abnormality is determined for read output signal characteristic data, the controller stores in memory the output signal characteristic data as white reference data.