[AstroPy] normalizing pictures from camera at various settings

Eyal Saiet ejsaiet at alaska.edu
Wed Dec 9 03:28:48 EST 2015

Excellent, with some image processing, I can get average DN values of
several stars excluding the rest of the night sky in the image.
Thanks Evert!
On Tue, Dec 8, 2015 at 11:00 PM, Evert Rol <evert.rol at gmail.com> wrote:

>   Hi Eyal,
> > Hello colleagues,
> > I did not get any replies to my question. One idea that stroke me was to
> assume the brightens of stars is constant and use its DN value to normalize
> my images? I need to dig more into this, but thought maybe someone would
> have feedback?
> Yes, that would be the most sensible thing to do.
> The sky background is not that constant that you can histogram it and
> compare between observations: moon and other background light can influence
> it. The stars should remain relatively constant.
> You want to perform seeing-matched aperture photometry for the best
> results (if that's manageable or relevant for your images), so that the
> fraction of light/counts for each star is the same between images.
> There is a chance you have some variable stars in your images; if you make
> sure you use enough stars, you can fairly easily filter out the variable
> stars and ignore those in your analysis.
>   Evert
> > Hello,
> > I am taking an image processing class. My class project involves working
> with given camera images of the night sky. Because the camera is set at at
> auto, I cannot compare intensity of two images(camera sensitivity varies
> due to changes in shutter speed, aperture, and ISO). Is there any algorithm
> you would recommend that can infer what the dark night sky should look like
> in the histogram, and use that information to adjust the histogram,
> therefore enabling me to compare  two image DN values, from different
> camera settings?
> >
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