I have taken photos at different exposures from different places of the Orion constellation. I wish to find the effect of skyglow on the limiting magnitude of stars in the Orion constellation. How can I estimate the limiting value of any star from its RGB pixel value in the photograph?
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$\begingroup$ What image analysis software are you using? There are quick easy tricks if you're using something like DS9 (it's free), but it could be MUCH more difficult using something like ... MSpaint. $\endgroup$– LaserYetiJan 18, 2017 at 6:09
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$\begingroup$ The files that I am working with are in NEF format. DS9 doesn't seem to support NEF, or even JPG, for that matter. $\endgroup$– Shashank AcharyaJan 18, 2017 at 7:16
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$\begingroup$ Try converting to something DS9 can use. Astronomers tend to use FITS file format and I'm sure you can find some free software to do this. NEF and JPG are not good choices for image analysis. $\endgroup$– zephyrJan 18, 2017 at 13:49
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$\begingroup$ Seems I answered this very question a day or two ago, but I can't remember in which SE site :-( $\endgroup$– Carl WitthoftJan 18, 2017 at 14:21
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$\begingroup$ With DS9, you can open any GIF, JPEG, TIFF, PNG, PPM, using the "File" - "Open Other" - "Open Photo". Granted, on my windows machine this crashes DS9 every time, with anything other than a FITS file, but it works like a charm on my Linux machine. Not too sure about NEF files though. I just broke my wife's nikon, otherwise I'd check it out. Either way, I'd suggest converting the files, or finding another analysis tool. Sorry. $\endgroup$– LaserYetiJan 19, 2017 at 5:51
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