| 摘要 |
PROBLEM TO BE SOLVED: To eliminate a joint appearing in an image by positioning a mask on a photodetector system and making an opening in the mask thereby compen sating for a detected error. SOLUTION: A pair of photodetectors 120, 122 are arranged in the image plane at one end of an image plane 43 on the outside of the scanning range of an imaging system. The pair of photodetectors 120, 122 are offset to the inside of the image plane 43 and a mask 124 is provided with an appropriate recess 126 so that the image plane 43 will be flush with the mask face. The mask 124 is formed in an opaque supporting part 130 and a pair of triangular openings 128, 128' are made back to back while being spaced apart by a predetermined distance D corresponding to the width of a stick region 20. The mask 124 is positioned in the recess 126 and the triangular openings 128, 128' are laid directly on the photodetectors 120, 122, respectively, thus compensating for the ink scan error of an image beam.
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