Author Topic: Purple and cyan Stars DSLR  (Read 951 times)

Offline frasax

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Purple and cyan Stars DSLR
« on: 2017 February 22 13:56:50 »
Hi,

i´ve processed my first image completely in PixInsight. Its a 2hours Image of the Milkyway with a Canon 6D and a 24mm Lens.
In the final image you can see that most of the bright stars are purple or do have purple centers, while dim stars have a cyan color cast (see attached crop).

Here is what i did:

BatchProcessing (against all recommendations) of Flats, Bias and Lights
Linear Fit to Green
Background Neutralization
ColorCalibration
SCNR remove green
Masked Strech

Do you have any ideas if i did something wrong here, or how i could avoid this.

CS Frank

Offline wimvb

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Re: Purple and cyan Stars DSLR
« Reply #1 on: 2017 February 26 09:20:53 »
Did you repair the star cores before MS? Have a look here.

http://pixinsight.com.ar/en/info/processing-examples/28/maskedstretch-stars-sores.html

Also, since MS doesn't stretch stars as much as nebulosity, you may have to apply a histogram stretch or curves stretch to enhance contrast and brighten the stars.
Wim

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Offline akulapanam

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Re: Purple and cyan Stars DSLR
« Reply #2 on: 2017 February 26 22:30:34 »
You can try repair hsv separation script but it also could be a result of being slightly out of focus (happened to me with osc and hyper star ever so often) or some chromatic abberation.

Offline EelkoGielis

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Re: Purple and cyan Stars DSLR
« Reply #3 on: 2018 January 13 13:33:02 »
Hi, it's been a while back, but I have the same issue with my Nikon D4s camera images from BPP.

This is all before any stretching.

Image data: 71 lights, 61 flats, master bias and dark, target M42, camera Nikon D4s, telescope Celestron 9.25" EdgeHD in prime focus.
Celestron 9,25" Edge HD, SkyWatcher NEQ6Pro, Lacerta MGEN on F500mm f90mm APO

Offline pfile

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Re: Purple and cyan Stars DSLR
« Reply #4 on: 2018 January 14 08:27:49 »
the stars are overexposed... as a consequence of how DSLR files are handled in PI you sometimes get a pink/red core instead of white when the core is overexposed.

i think you *might* be able to fix this by splitting the channels and then using Rescale on each channel and finally re-combining the channels. or perhaps Rescale works on RGB images, i am not sure.

alternately you could make some shorter exposures which dont blow out the stars and use HDRComposition to blend the data together.

rob