| 摘要 |
PURPOSE:To avoid the omission of data at the CCD end part and to optionally control the contrast by discriminating the control bias values within a prescribed period at the start and the end of a single scan period of the CCD data from those control bias values in other periods. CONSTITUTION:The bias circuits 4(1) and 4(2) control the current values of transistors TRQ1 and Q2 and output the contrast control bias signals 4(1)a and 4(2)a. The base potential of the TRQ2 of the circuit 4(2) is kept at a fixed level and the signal 4(2)a is set at a fixed low level regardless of pictures. While the circuit 4(1) varies the resistance value of a variable resistance R2 in the resistance string of a resistance R1, a variable resistance R2 and a resistance R3 in accordance with the pictures and then controls the base potential of the TRQ1. Then the value of the R1 is increased more than the level of the signal 4(2)a even though the R2 is equal to zero. The signal 4(1)a is controlled so that an optimum contrast is secured for a binary signal.
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