After the camera lens is photosensitive, the optical signal is sent to the sensor. The conversion of the optical signal from the sensor to the electrical signal is usually caused by thermal noise. Obtain the current value of the raw image from the lens completely blocked as the clamp value.
The removal of Hot noise is the average thermal noise value (current value) introduced when the total pixel value is subtracted from the total black ).
Thermal Noise = pixels values-average (optical black)
Figure: Optical black clamp
After the optical black clamp is performed on the image, some details of the image will be lost, and the image color will be affected. Generally, after the camera ISP completes debugging, it is necessary to reduce the black clamp to enhance the image details, so that more useful information is available in the image.
References:
[1] Bo-ching Huang, chiou-shann fuh, "image pipeline algorithms for standard mobile imaging ure sensors" Department of Computer Science and Information Engineering,
National Taiwan University 2005.