| 摘要 |
PROBLEM TO BE SOLVED: To provide an image reading circuit for eliminating background density variations and variations in background density for each original when an ADF continuously reads originals. SOLUTION: The image reading circuit includes: a carrying means for ADF originals to read the originals while moving the originals; a peak detection circuit for tracking a peak value of an image signal by repeating storage and discharge of the peak value, the image signal resulting from a CCD 1 comprising a plurality of elements arranged at a prescribed position in the main scanning direction and reading a reflected light from the original side; and a circuit for determining a lower limit for the density of originals to eliminate a background, and the image reading circuit eliminates the background of a read image on the basis of an upper limit voltage of an A/D converter 3 determined from the peak value detected by the peak detection circuit, varies the lower limit of the background elimination density at any time at the same time when a lamp luminous quantity is attenuated to eliminate the background of the read image when the ADF continuously reads originals. COPYRIGHT: (C)2005,JPO&NCIPI
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