| 摘要 |
This invention is related to an image reading apparatus for use in a digital copy machine and a facsimile machine. The invention is made possible to obtain the simple flat average value of the white reference data used for a shading correction obtained with a photoelectric conversion elements arranged in a line by sensing the reflected light upon a white reference plate. The image reading apparatus comprises an n-bit memory for the white reference data and another n-bit memory for the black reference data and a reference data processing circuit for summing white reference data after 2m times of line readings on the white reference plate. The summation of the data is carried out with the use of an n+m bit memory region, consisting of an upper n bit section and a lower m bit section, that is made up with the n-bits of the n-bit memory of the white reference data and m-bits of the n-bit memory of the black reference data. Then after summation of 2m data is completed, the data stored in the upper n-bit region of the (n+m) bit memory region coincides with +E,fra 1/2+EE mx(summation of the 2m white reference data), that is in fact a simple average value of the summed up data.
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