| 摘要 |
PURPOSE:To use a low-speed A/D conversion circuit, by making writing speed in storing data on shading distortion in a memory slower than memory reading speed. CONSTITUTION:Shading distorsion for determining a slice level, i.e, the reference voltae of a comparator 7 is read and stored in a memory 5. In this case, a circuit of low-speed system is used as an A/D conversion circuit 3, a sampling signal phis of 100KHz which is slower than a clock signal phic of 1MHz that drives an image sensor 1 is supplied from a timing generation circuit 4 to the circuit 3. The same place of an original is scanned repeatedly by a sensor 1 and the sampling position is shifted. By this way, the same data as in the case where scanning speed of the sensor 1 is A/D-converted at the same speed can be stored in the memory 5. |
