New answers tagged webcam
When using CCD and CMOS sensors, the distribution of the DC component of the sensor noise rarely changes with time (unless you plan on using your camera in extreme temperatures). This allows for effective factory measurement and calibration which allows them to measure and remove the dark frame automatically. So I don't think there is much use in trying to ...
What is probably going on has little to do with the camera sensor, per se. When the signal from the sensor is processed there is noise reduction applied. It seems that in the case of your webcam, the processor recognizes a "noise only" black frame and goes ahead and eliminates all of the signal to get rid of the noise.
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