[AstroPy] normalizing pictures from camera at various settings

Evert Rol evert.rol at gmail.com
Wed Dec 9 03:00:16 EST 2015

  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.


> 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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