| 摘要 |
PURPOSE:To read a document image as the one with high quality, and high resolution, by providing a band-pass filter in which a frequency smaller than a Nyquist frequency corresponding to the sampling interval of the document image as a center frequency, and correcting an image read by a line sensor. CONSTITUTION:The band-pass filter having a characteristic shown in figure A, and the peak of a gain at 3/8 of the frequency a little smaller than the Nyquist frequency (fn), for example, a sampling frequency, and with high sensitiveity for a high frequency component, is used as an MTF(modulation transfer function) correcting filter. As a result, the enhancement of the signal component of the Nyquist frequency for whose reliability is lowered by the reduction of the MTF, can be prevented. Simultaneously, the periodical fluctuation of a level caused by the use of amplifiers 22a and 22b separately for even-th and odd-th scans in a main scanning direction, can be eliminated. Also, since the signal component in the neighborhood of the frequency component of the peak of the gain is enhanced, the blur of the image can be corrected.
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