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PixInsight => General => Topic started by: barque on 2018 March 02 13:06:52

Title: Processing Question: Where did the color go?
Post by: barque on 2018 March 02 13:06:52
I'm trying to up my processing game and learn more about PixInsight. Using some sample data posted by Jerry Lodriguss (http://www.astropix.com/html/i_astrop/practice_files.html (http://www.astropix.com/html/i_astrop/practice_files.html)), I used the batch preprocessing script to calibrate, align, and stack the data. After applying DBE, SCNR, and a screen stretch, the image is full of detail but the color is completely washed out. Some of the color comes back if I stretch the red channel or increase the saturation, but I am missing something in how to process.

By comparison, processing a single light frame via Adobe Camera Raw with a stretch in Photoshop shows that there's lots of color in the raw data. Can somebody please point me in the right direction to recover the color in PixInsight? Thanks!!

Rob
Title: Re: Processing Question: Where did the color go?
Post by: pfile on 2018 March 02 13:29:00
having to boost the saturation is totally normal... ACR is doing that for you behind the scenes.

rob
Title: Re: Processing Question: Where did the color go?
Post by: sharkmelley on 2018 March 02 14:37:06
Quote from: barque
I'm trying to up my processing game and learn more about PixInsight. Using some sample data posted by Jerry Lodriguss (http://www.astropix.com/html/i_astrop/practice_files.html (http://www.astropix.com/html/i_astrop/practice_files.html)), I used the batch preprocessing script to calibrate, align, and stack the data. After applying DBE, SCNR, and a screen stretch, the image is full of detail but the color is completely washed out. Some of the color comes back if I stretch the red channel or increase the saturation, but I am missing something in how to process.

By comparison, processing a single light frame via Adobe Camera Raw with a stretch in Photoshop shows that there's lots of color in the raw data. Can somebody please point me in the right direction to recover the color in PixInsight? Thanks!!

Rob

The stretching that ACR performs will maintain colour although the stretch in Photoshop that you subsequently perform will lose some of that saturation.  Generally speaking all stretching operations will lose saturation, including the screen stretch.  It's why I wrote the ArcsinhStretch module: https://pixinsight.com/doc/tools/ArcsinhStretch/ArcsinhStretch.html

It has been purposely designed to prevent the loss of saturation during the stretch.

Mark

Title: Re: Processing Question: Where did the color go?
Post by: ChoJin on 2018 March 02 15:55:04
arcsinh is indeed great for color preservation, but unfortunately like maskedstretch you lose contrast compared to a HT stretch
Title: Re: Processing Question: Where did the color go?
Post by: barque on 2018 March 03 16:58:29
Thanks all. Haven't completely figured out how to get all the color back (as I see in the ACR version) but I'll keep working on it!
Title: Re: Processing Question: Where did the color go?
Post by: dpaul on 2018 March 03 17:40:16
Hi Cho,

How about doing partially with Arcsinh and Histogram Transformation Stretch to get color and contrast?

Thanks

David
Title: Re: Processing Question: Where did the color go?
Post by: RickS on 2018 March 03 21:38:26
You can also boost saturation easily with a clipped lum mask and CurvesTransformation.
Title: Re: Processing Question: Where did the color go?
Post by: dpaul on 2018 March 04 01:39:37
thanks again Rick

David
Title: Re: Processing Question: Where did the color go?
Post by: ChoJin on 2018 March 04 06:07:28
@dpaul I'm currently experimenting with combining the arcsinh and HT stretches with a (star)mask and some pixel math magics (ideas taken from https://pixinsight.com/tutorials/NGC7023-HDR/index.html , the "High-Contrast, Small-Scale Structures" part). It seems to work great to get my star's shapes and colours back. They don't look like flat discs anymore.

I've also seen in another topic someone doing RGB stretch with arcsinh and L stretch with HT and LRGB combination to combine them. I haven't tried that yet.
Title: Re: Processing Question: Where did the color go?
Post by: dpaul on 2018 March 04 16:03:30
Thanks Cho

David