| 摘要 |
PURPOSE:To directly form an optical black and to set a correct and stable black reference level by providing a means for controlling the photoelectric transmissivity of a desired part on an image pickup surface. CONSTITUTION:In an ordinary reading operation, liquid crystal shutters OB1, OB2 are transparent by a switch 110. Initially, a start pulse phis1 is inputted to a horizontal blanking period and a horizontal shift register 106 sequentially outputs a scanning pulse phiH in a constant operating frequency fs. At the same time, clamp pulse phicp is inputted to a clamp circuit 109 and a reference level is set by the signal of the leading OB1. Thereby, a signal in which the black reference level is fixed is outputted for every horizontal line from the clamp circuit 109. Then, the shutter OB2 is shielded the light and an OB3 is transparent by the switch 110. A start pulse phis2 is applied to the register 106 and the scanning pulses are sequentially outputted at the frequency fs/2 by pulses phi1, phi2. The signal of the leading OB2 is read and the black reference level is set in the circuit 109 according to the pulse phicp.
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