Re: Negative values on the histogram - what do they mean?

Posted by karenacollins on Jan 08, 2022; 6:51am
URL: http://astroimagej.170.s1.nabble.com/Negative-values-on-the-histogram-what-do-they-mean-tp1713p1739.html

It is possible that after bias and dark subtraction, bad/dark pixels can go negative, and in the case of low sky background, random bias or other variations can cause small negative values. In general, the mean of your calibrated science image should be close to the mean of your raw science image minus the mean of your master bias minus the average value of your master dark. If your camera software adds a pedestal value, you'd need to subtract that amount too. If you find this to be the case, then I think your calibration is probably okay.

Karen