Image reading apparatus and image reading method

摘要

An image reading apparatus capable of accurately detecting abnormal pixels caused by a contaminant such as dirt, stain, or flaw on a moving document reading glass being read. An image processing unit of the image reading apparatus performs a first abnormal pixel detection process to detect pixel signals representing abnormal pixels and output from image sensors for respective colors when a reading unit reads a guide plate in a main scanning direction in a state before an original passes through a moving document reading position, performs a second abnormal pixel detection process to detect pixel signals representing abnormal pixels and output from the image sensors when an original being conveyed is read by the reading unit in the main scanning direction, and detects a main scanning direction of abnormal pixels based on results of these detection processes.

主权项

1. An image reading apparatus comprising:
an original conveyance unit configured to convey an original so as to be introduced into between a moving document reading glass and a reference member and so as to pass through a moving document reading position, the moving document reading glass and the reference member being disposed to face each other at the moving document reading position; a reading unit configured to read the original in a main scanning direction through the moving document reading glass when the original passes through the moving document reading position; a first abnormal pixel detection unit configured to detect a pixel having abrightness value less than a first abnormal pixel detection threshold value among pixels located at a same main scanning direction position in a plurality of lines, the brightness value being obtained by said reading unit reading the reference member through the moving document reading glass in a state before the original passes through the moving document reading position, said first abnormal pixel detection unit being configured to detect, in a case where the number of detected pixels is equal to or greater than a first abnormal pixel determination threshold value, a main scanning direction position of the detected pixels as a first main scanning direction position; a second abnormal pixel detection unit configured to detect a pixel having a brightness value less than a second abnormal pixel detection threshold value, the second abnormal pixel detection threshold value being greater than the first abnormal pixel detection threshold value, among pixels located at a same main scanning direction position in a plurality of lines, the brightness value obtained by said reading unit reading a leading end portion of the original through the moving document reading glass in a state that the original is being conveyed, said second abnormal pixel detection unit being configured to detect, in a case where the number of detected pixels is equal to or greater than a second abnormal pixel determination threshold value, a main scanning direction position of the detected pixels as a second main scanning direction position; and a decision unit configured to decide the main scanning direction position detected both as the first main scanning direction position and as the second main scanning direction position, as an abnormal main scanning position.