JPS57119565A - Picture-signal correction system - Google Patents

Abstract

PURPOSE:To use a low-speed A/D converter by reading a reference surface several times by an image sensor, by finding corrected values of some bits by performing A/D conversion every time the reference surface is read, and by finding corrected values of all bits finally. CONSTITUTION:Before picture information is read, a white reference surface is read by an image sensor and a digital signal (e) obtained by processing the obtained analog signal by A/D conversion 8 through a sample holding circuit 7 is used to address an ROM9, thereby writing a corrected value from the ROM9 in an RAM10. When the quantity of light from a light source becomes constant during the repetition of said operation, the level of the signal (e) becomes constant and once a light-quantity detecting circuit 12 detects that, an N-time read control circuit 15 supplies a frequency-division clock P to each circuit. The output of the circuit 7 is processed by A/D conversion 8 at a low frequency 1/N to store corrected values of respective bits in the RAM10, so that corrected values of all bits are stored finally. Then when an actual original is read, a subtracter 11 subtracts the corrected value of a corresponding bit from the RAM10 from the output of the circuit 7, thus correcting variance in ref- erence level.