| 摘要 |
PROBLEM TO BE SOLVED: To detect deterioration in a wide received light quantity caused by the belt-like dirt, etc., on a shading correction roller, which is difficult conventionally. SOLUTION: One main scanning line is divided into plural blocks, the average of each is calculated, the respective averages are compared, a discrimination flag corresponding to the difference is generated and based on the number and the generating order of each discrimination flag, the presence/absence of the belt-like dirt at the shading correction roller is detected.
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