| 摘要 |
PURPOSE:To compensate the reduction of the level of a picture signal which is caused by the deterioration of the illumination light volume of a reading light source, by reading a standard white surface simultaneously with an image surface with a reading element and setting the level at a constant value for the area corresponding to the white surface. CONSTITUTION:A light source 2 irradiates an original, and a reading element 1 gives the photoelectric conversion to the reflected light of an original irradiated by the light source 2. A standard white surface 3 is set on the scanning surface of the original. A digital control type variable attenuator 7 attenuates the output picture signal of the element 1. An extracting means extracts the reading picture signal of the surface 3 out of the output picture signal of the attenuator 7. A comparator 11 compares the output signal of the above-mentioned extracting means with a prescribed reference level signal. a counter 16 controls the degree of attenuation of the attenuator 7 based on the result of comparison of the comparator 11. Then the level is kept constant for the part corresponding to the surface 3 among the output signals of the attenuator 7. |
