OSC Camera - How get colors closer to accurate?

Questions and answers about processing in StarTools and how to accomplish certain tasks.
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F-Astro
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Location: Northwest Arkansas, USA

OSC Camera - How get colors closer to accurate?

Post by F-Astro »

Hi,

I am using a ZWO ASI294MC Pro one shot color (OSC) camera. I am having trouble with some files getting an accurate color rendition using the Scientific Color Constancy option in the color module. I'm hopeful someone can educate me on the best workflow to use.

The images below show some quick and dirty processing of the Iris Nebula (NGC7023). Bin-->Autodev--> Wipe-->Crop-->Autodev-->Life (isolate) --> mask by hand about 25 star cores --> Color (scientific), then remove, invert mask. The other image is the color wavelength response curve of the 294 sensor.

My normal generic workflow would include contrast, sharpening and deconvolution, and possible HDR. Any guidance is appreciated.
Attachments
ASI294 Color Response
ASI294 Color Response
Screenshot 2020-09-11 110414.gif (59.81 KiB) Viewed 258 times
File after Wipe
File after Wipe
wiped1.jpg (404.61 KiB) Viewed 258 times
File in Color Module
File in Color Module
color1.jpg (201.63 KiB) Viewed 258 times
elpajare
Posts: 84
Joined: Tue Jun 12, 2018 6:13 pm

Re: OSC Camera - How get colors closer to accurate?

Post by elpajare »

It would be very useful to have an original file (a jpg is worth it for me) without treatment, to be able to compare different workflows.

I use this same chip ( IMX294 C uncooled) and Startoos gives me very high color fidelity, it all depends on how you use it.

I am interested in this topic ...
F-Astro
Posts: 12
Joined: Sun Aug 30, 2020 2:09 pm
Location: Northwest Arkansas, USA

Re: OSC Camera - How get colors closer to accurate?

Post by F-Astro »

OK, file was stacked with all recommended StarTools settings. Note that anybody who looks at this will need to crop out the strong blooming/lensing/?? effect at the top. I have no idea what is causing it, as CMOS sensors are not supposed to be susceptible to blooming and the 294 sensor is not known for any micro-lensing. I have a support request for ZWO in and have a post on Cloudy Nights hoping someone can tell me what it is. I have seen it on several of my images lately and it is near impossible to get around in post. Anyway, here is the link:

https://drive.google.com/file/d/1HQZTWO ... sp=sharing

Thanks for any and all help.

Fran
elpajare
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Re: OSC Camera - How get colors closer to accurate?

Post by elpajare »

My opinion is not that of a specialist, please take it with reservations.
Image has hideous rectangular vignetting. Stacking program problem?
It also has a very horrible gradient, I have also used Wipe at 90% !!
For the rest, the result is this that I put you. If it seems correct enough, I will tell you how I got here.
Attachments
Autosave001 ST2.jpg
Autosave001 ST2.jpg (406.22 KiB) Viewed 247 times
F-Astro
Posts: 12
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Location: Northwest Arkansas, USA

Re: OSC Camera - How get colors closer to accurate?

Post by F-Astro »

elpajare wrote: Fri Sep 11, 2020 10:07 pm My opinion is not that of a specialist, please take it with reservations.
Image has hideous rectangular vignetting. Stacking program problem?
It also has a very horrible gradient, I have also used Wipe at 90% !!
For the rest, the result is this that I put you. If it seems correct enough, I will tell you how I got here.
Thanks for taking a look. I’m afraid that I don’t know what rectangular vignetting is, if you could explain I would appreciate it. I’m new to long exposures Astro imaging, coming from an alt-az mount and EAA, so extensive post processing is new to me. I do understand signal processing, having worked with it in geophysical industry for many years, but Astro data has its own set of issues. Can you hazard a guess on why I am having gradient issues? I live/image in Bortle 4 skies, so wouldn’t expect light pollution issues.

I can get to a similar issue as you posted, but I need to basically disregard most of the scientific constancy and play with color bias sliders. I would be interested in your workflow.

Sorry for all the questions. Do appreciate you taking your time to respond.
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admin
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Re: OSC Camera - How get colors closer to accurate?

Post by admin »

Note that there may be some impossible-to-correct color skew if you did not use a UV/IR cut filter (see here on why).

@elpajare
Image has hideous rectangular vignetting. Stacking program problem?
DSS has a long standing issue where even if you use Interesection mode, it leaves border of exactly one pixel (if you zoom in, you will see these tiny stacking artifacts). As you know, any dark anomalies and stacking artifacts will make Wipe back off in their vicinity, as it regards them as "background" that must be preserved. Just crop the image a little and Wipe behave correctly.
Ivo Jager
StarTools creator and astronomy enthusiast
elpajare
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Joined: Tue Jun 12, 2018 6:13 pm

Re: OSC Camera - How get colors closer to accurate?

Post by elpajare »

My advice is of limited value because my experience is solely at EAA. What I can tell you is that if the gradient is produced by UV / IR rays ( Ivo said), I always use this filter for the IMX294C chip and it works quite well for me:

https://www.astroshop.es/filtros-l-rgb/ ... 5-/p,49261

Regarding the stacking, I use the original capture program of my camera and it does not give me any problem of strange artifacts. I do not know why you use other stacking programs those of AstroPhoto.

My workflow is very simple, the only important thing is to cut out the artifact areas and eliminate the gradient. If you do this your colors will be like the ones I got.

This is the Workflow:

Bin / Crop / Wipe (90% intensity) / Autodev (ROI) / Flux (Noise) / Color (Artistic + maxRGB adjust) / Track off> Denoise /

Each step has specific settings that may vary, so you better try.

If you have a problem in one of them I will try to help you

Good luck friend!
F-Astro
Posts: 12
Joined: Sun Aug 30, 2020 2:09 pm
Location: Northwest Arkansas, USA

Re: OSC Camera - How get colors closer to accurate?

Post by F-Astro »

admin wrote: Sat Sep 12, 2020 2:56 am Note that there may be some impossible-to-correct color skew if you did not use a UV/IR cut filter (see here on why).

@elpajare
Image has hideous rectangular vignetting. Stacking program problem?
DSS has a long standing issue where even if you use Interesection mode, it leaves border of exactly one pixel (if you zoom in, you will see these tiny stacking artifacts). As you know, any dark anomalies and stacking artifacts will make Wipe back off in their vicinity, as it regards them as "background" that must be preserved. Just crop the image a little and Wipe behave correctly.
Thank you Ivo. I do routinely crop several pixels around the border just to make sure, and I will invest in a IR/UV filter.
F-Astro
Posts: 12
Joined: Sun Aug 30, 2020 2:09 pm
Location: Northwest Arkansas, USA

Re: OSC Camera - How get colors closer to accurate?

Post by F-Astro »

elpajare wrote: Sat Sep 12, 2020 7:06 am My advice is of limited value because my experience is solely at EAA. What I can tell you is that if the gradient is produced by UV / IR rays ( Ivo said), I always use this filter for the IMX294C chip and it works quite well for me:

https://www.astroshop.es/filtros-l-rgb/ ... 5-/p,49261

Regarding the stacking, I use the original capture program of my camera and it does not give me any problem of strange artifacts. I do not know why you use other stacking programs those of AstroPhoto.

My workflow is very simple, the only important thing is to cut out the artifact areas and eliminate the gradient. If you do this your colors will be like the ones I got.

This is the Workflow:

Bin / Crop / Wipe (90% intensity) / Autodev (ROI) / Flux (Noise) / Color (Artistic + maxRGB adjust) / Track off> Denoise /

Each step has specific settings that may vary, so you better try.

If you have a problem in one of them I will try to help you

Good luck friend!
I use Deep Sky Stacker, which is dedicated astronomy stacking software.

I plan to look for any light leaks possibly causing problems and retaking calibration frames. I also will get a UV/IR filter. That is probably my main issue with the color module as I sometimes see a color cast when the scientific module computes the color spectrum.

Many thanks for taking your time to respond.

Fran
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