| 摘要 |
PURPOSE:To read the density of an original regardless of the size of the original or the open/close of a pressure plate, by counting the changing points of variable density of the original and deciding the front or rear edge of the reading timing of the original density from the result of the above-mentioned count value. CONSTITUTION:An original is scanned and moved before an image of the original is formed, and the density of the original is detected by a photoamplifier 1. The output of detection is supplied to a positive peak holding circuit 5 and a negative peak holding circuit 8 via a logarithm amplifier 2 and a buffer 3. The outputs of the circuits 5 and 8 are inverted and added together to obtain the signal proportional to the mean value of the original density. The switches 4 and 7 are provided at the front stages of the peak holding circuits 5 and 8 respectively. While a part of the output of density detection undergoes the waveform shaping, and then the changing points of an original density pattern. Then a circuit 13 discriminates the starting time for reading the maximum and minimum densities of the original. Based on the output of this discrimination, the switches 4 and 7 are opened and closed to control the start of reading. |
