| 摘要 |
PURPOSE:To binary-code surely picture information even if the density and reflection factor of external light and recording information are changed, by obtaining a threshold voltage signal from a minimum value and a peak value of a picture signal and a shading waveform signal. CONSTITUTION:The shading waveform signal is stored in advance in a shading waveform signal reproducing circuit 3 every start of reading of an original. A peak value VP and a minimum value VL are detected respectively at a peak value detecting circuit 1 and a minimum value detection circuit 2 from a picture signal VS corresponding to a line and held in sample-and-hold circuits 4, 5 until the picture signal corresponding to the next line is obtained. The shading waveform signal is read out from the circuit 3 in synchronizing with the picture signal corresponding to the next line and a waveform synthesis circuit 6 generates or controls a threshold voltage VTH based on the values VP and VL from the circuit 4, 5 and the shading waveform signal. Thus, the voltage VTH of the picture signal is compared at a comparison circuit 7 and binary-coded. |
