Patent ID: 8223228

Claim:
An image signal processing apparatus for applying processing to image signals from a solid state image sensor having a plurality of effective pixels and a plurality of light shielded pixels configured to output an optical black outputs, comprising: an optical black level determining portion configured to compare the optical black outputs from the light shielded pixels with a predetermined clamp level and outputting as difference outputs a difference between the optical black outputs and the predetermined clamp level; a holding portion configured to hold the difference outputs; an adding and subtracting circuit configured to clamp the image signals in accordance with the difference outputs; a control unit configured to selectively transmit the difference outputs to the holding portion, wherein the control unit includes a comparator configured to compare the difference outputs of the light shielded pixels with a predetermined comparison level, and a counter portion configured to count the number of times that the difference outputs are larger than the predetermined comparison level, wherein when the number of times that the difference outputs are larger than the predetermined comparison level exceeds a predetermined number of comparison times, the control unit blocks further transmission of a difference output to the holding portion, and wherein an already-held difference output is output from the holding portion to the adding and subtracting circuit.