A
astropixel
Guest
I have taken a completely different approach to this DSLR image business. Re-reading Craig Stark's paper, I conclude that the modification of DSLR RAW data in-camera warrants a different method of calibration.
Based on nothing more than a hunch - very unscientific - I ran a few preprocessing exercises using different combinations of frames for calibration. The method that produced scaling factors near 1.0, with consistent noise estimates across all channels and weights near 1, was considered valid. Presuming that these results are desirable.
Except for the use of Multiplicative and Equalize Flux for flat frame integration, all other frames were integrated with the same parameters as the light frames. Flats were calibrated with a bias frame, but the dark was not. Light frames were batch processed with a master dark (no bias subtraction) and master flat only.
Frame set, as follows; -5C ISO800, 66 bias, 12 dark, 18 flats and 18 lights
Master frame Mean - bias 255, dark 255, flat with bias subtraction 800 (1056 without bias subtraction)
Scaling factors 1.0, Noise estimates ~7, Weights ~0.99 - 0.98.
These are the most consistent results to date. Certainly cold finger, accurate, regulated cooling has an influence on the residual dark current value. It's not high and personally, I think the bias is better left in the dark in this case - for best results.
Superbias may however, produce different results.
EDIT: http://pixinsight.com/forum/index.php?topic=7079.msg47768#msg47768
Based on nothing more than a hunch - very unscientific - I ran a few preprocessing exercises using different combinations of frames for calibration. The method that produced scaling factors near 1.0, with consistent noise estimates across all channels and weights near 1, was considered valid. Presuming that these results are desirable.
Except for the use of Multiplicative and Equalize Flux for flat frame integration, all other frames were integrated with the same parameters as the light frames. Flats were calibrated with a bias frame, but the dark was not. Light frames were batch processed with a master dark (no bias subtraction) and master flat only.
Frame set, as follows; -5C ISO800, 66 bias, 12 dark, 18 flats and 18 lights
Master frame Mean - bias 255, dark 255, flat with bias subtraction 800 (1056 without bias subtraction)
Scaling factors 1.0, Noise estimates ~7, Weights ~0.99 - 0.98.
These are the most consistent results to date. Certainly cold finger, accurate, regulated cooling has an influence on the residual dark current value. It's not high and personally, I think the bias is better left in the dark in this case - for best results.
Superbias may however, produce different results.
EDIT: http://pixinsight.com/forum/index.php?topic=7079.msg47768#msg47768