| 摘要 |
PURPOSE:To improve the resolving power of the device by effectively utilizing the resolving power of an A/D converter 7. CONSTITUTION:An exposing lamp 2 is moved along an original 1 and the light rays reflected from the plural measurement points of the original 1 are received by a sensor 4 and are photoelectrically converted. The signals thereof are supplied through to an I/V conversion circuit 21, a low-pass filter circuit 22 and a gain selection circuit 5 to a toe cutting circuit 23. Only the signals of the range necessary for deciding the density of the original 1, for example, the signals corresponding to a reflection density OD=0.0 to 0.3 range are extracted. Such a gain as to meet the input level width of the A/D converter 7 when the signals of this range are amplified is selected in the gain selection circuit 5. While the signals corresponding to the reflection density OD=0.0 to infinity are heretofore processed in the A/D converter 7, the signals of the narrow range up to OD=0.0 to 0.3 are processed by the A/D converter 7 in this embodiment and, therefore, the resolving power of the device is improved by using the A/D converter 7 having the same resolving power as the resolving power of the conventional converters. |
