| 摘要 |
PURPOSE:To extract surely black information from picture information by applying tracking control to a white level signal depending on a stored white level signal and an input signal. CONSTITUTION:Pattern information on a medium is formed into a signal L to be measured via a photoelectric converting element 1 and a sample holding circuit 3, inputted to a comparator 4, the signal L and a white level signal L' are compared at each bit, and when L>L', the white level set in a counter 5 is updated and the value of a white level register 11 is updated by this update value. When L<L', a binary-coding threshold value of a set circuit 7 and the signal L are compared 8 and the output is stored in a register 9. Further, bit information before one scanning is outputted from the register 9 and a signal without black information is outputted from the comparator 8, and contents of the counter 5 are updated by the output of an AND circuit 10. |
