This invention relates to an image reading apparatus for photographing a document such as a book which is placed face up, and especially to an art for reading out an image of the document with accuracy.
Conventionally, as to the image reading apparatus for the document placed face up, there has been provided an apparatus which detects an image including both of a finger pressing the document and the finger shadow (the image of this kind is hereinafter referred to as finger area) out of an image which is read out by an image reading sensor based on a brightness difference between a brightness of a document ground and a brightness of a finger area, and erases the finger area from the read-out image (e.g., refer to U.S. Pat. No. 5,377,019). On the other hand, there has also been provided an apparatus which detects marginal spaces in right and left edges of the document (blank area other than the area having letters and photographs, or other than the finger area), and erases an image outside the marginal spaces from a read-out image, thereby erases the image of the finger area which is normally positioned outside the marginal spaces (e.g., refer to U.S. Pat. No. 5,677,776)
However, in the above-mentioned conventional image reading apparatus, there has been a problem that a letter image lying into a finger shadow of the finger area is erroneously erased in the image erasure operation for the finger area since such a letter image cannot be distinguished and isolated from the finger area.