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

Posted by karenacollins on Jan 07, 2022; 10:45am
URL: http://astroimagej.170.s1.nabble.com/Negative-values-on-the-histogram-what-do-they-mean-tp1713p1737.html

Hi Magnus,

If deBias was enabled when producing the dark, it should be checked when using the dark at a later time too. If deBias was on when you produced the master dark, but you turned deBias off when using the dark, then you should see an average difference in your calibrated images of 370 (i.e. the mean value of your Bias file). As long as you have deBias on or off when you create and use the master dark, then you should get the same result, although if your dark exposure time is different than your science exposure time, you should use the deBias option.

AIJ normalizes the flat to have a mean value of 1.0, so the range 0.851 to 1.4992 sounds reasonable. According to your information below, it seems that PixInsight is not normalizing the flat, which would explain the difference.

I'm not clear what you mean by "I get -7.739 for some images right now". Is that the lowest pixel value in the image? If so, that's not surprising, and I'm not sure there is a problem with your calibration process.

Karen