Old 27-05-2013, 07:09 PM
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whzzz28 (Nathan)
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Join Date: Dec 2011
Location: Brisbane
Posts: 341
Color correction

I have been going over my previously processed data and seeing if i can improved what i have.
What i have noticed is that most of my images lack color depth and during processing it is easy to destroy the image by trying to bring out the color - especially anything in the blue wavelengths.

Recently i took two nights worth of data on M83 with my VC200L, with high hopes that half of my troubles may be my old ED80 having color correction issues, but as i am having similar results with this data i realize that it is 100% my processing.

I normally use PI's ColorCalibration tool. I have used this with linear and non-linear data to different affect on different data. Generally i use it on linear data and use a screen stretch to check it.
I also recently have started playing around with ColorSaturation and Saturation (in curves) and shifting hues. I realize i am over-saturating my images to try and bring out color, which is destroying the data (and some stars), which leads me to believe my issue is color calibration.

Regardless of what PI tutorials or processing steps i read i am unable to, as i believe, get the best out of my data.
It always seems to be the blue data that is lacking.

So now i am throwing up a hand looking for any tips or hints.
I have included two processing attempts i have tried that got some success, however i am concerned that my galaxy arms look more aqua than blue (can be removed by doing an SCNR, 100% green removal). Also note the lack of star color on blue stars.
In preparation of blown out stars i took 3x 60s shots as well - but apparently that was too much, those stars are blown out as well

Finally if anyone wants to try out the data, i have uploaded the LRGB files for people to play with. There is a slight flat problem as well that i am unsure on (the ADU of the flats was as i normally have them, not sure why my flats were so bad, i even took another set the next night with higher ADU's and got the same results...)

Any comments are welcome. Or if you have processing steps you use, or a tutorial that you have followed, those would be helpful as well.
Considering a hefty gear upgrade, but unless i get my processing down it won't be worth it.

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Old 27-05-2013, 07:37 PM
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RickS (Rick)
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Join Date: Apr 2010
Location: Brisbane
Posts: 10,584

I haven't found a method that works 100% of the time but eXcalibrator often gets me a reasonable result: http://bf-astro.com/excalibrator/excalibrator.htm. The latest version is much easier to use too.

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