3 ms·
If the sensor is stable over the period when the frames are shot, why would subtracting the mean of the black frames from the mean of the exposures be worse tha
by username789 10y ago
If the sensor is stable over the period when the frames are shot, why would subtracting the mean of the black frames from the mean of the exposures be worse than subtracting individual black frames from individual exposures? Aside from rounding errors and possible overflows the two procedures should be equivalent:
(e1 + e2 + ... en) / n - (b1 + b2 + ... bn) / n = (e1 - b1 + e2 - b2 + ... en - bn) / n
- gjm11 10y agoThe suggestion isn't about what order you do the arithmetic in, but about what order you do the captures in. ++++---- versus +-+-+-+-. The former has the disadvantage that if something that affects the images (temperature, say) is varying gradually, or changes abruptly at a particular point, it's easier for it to have substantially different effects on the light and the dark frames. It's possible that something like Thue-Morse (+--+-++--++-+--+ etc.; one way to define this is to look at the parity of the number of 1-bits in the binary representation of the frame number) might be better than alternating. If whatever disturbances you might worry about are smooth in the right sort of way, it gives you more exact cancellation than alternating.