uring the operating, or integration, mode, visible photons generate electrons in the pixel cell of a CMOS image sensor. The pixel collects the electrons and then translates the accumulated charge to voltage signals that serve as an output. Expressing this process quantitatively, pixel responsivity is the relation between the electrical signal and its exposure to light (V/luxXsec). "Full-well capacity" is the number of electrons that the pixel can collect. Dynamic range is roughly the number of resolvable gray levels, which you calculate by dividing the maximum signal by the minimum detectable signal and usually report in decibels. Thermally generated electrons are obviously enemies of image sensors, because the pixel collects them along with optically generated electrons; they steal well capacity and add noise. Thus, the rate of the electrons' thermal generation within the pixel, or "dark current," is a major performance measurement that you generally report in electrons per second. Pixel development requires simultaneous optimization of all of the above parameters, along with a few additional ones-a major challenge within the world of pixel design.
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