After Preprocessing, How to Use Trichromy?

Image processing, astrometry, photometry, etc.
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dredger
Posts: 8
Joined: 31 Jan 2019, 01:47

After Preprocessing, How to Use Trichromy?

Post by dredger » 09 May 2021, 18:21

I've been using a monochrome with filters and have a set of RLGB images that have been through the preprocessing, 20m total exposure and darks and flats included for each filter.

Not sure what to do from here. Am I supposed to use trichromy with RGB, and then combine that with L? Am I supposed to combine all four resultant images again in preprocessing, subtracting darks again? Is there a work flow chart or something for Astroart7?

Anyway if there was a good link or reference regarding processing work. All I could find are videos 7-8 years old.

fabdev
Posts: 282
Joined: 03 Dec 2018, 21:43

Re: After Preprocessing, How to Use Trichromy?

Post by fabdev » 11 May 2021, 23:29

Hi, I suggest to start with L: do Preprocessing, (maybe save the settings if you want to repeat it later) then obtain the combined L image.
This will show you which level of S/N you can expect in your final LRGB image.
On the master L image, apply the filters you need (e.g. DDP, histogram stretch, noise reduction, sharpness etc). Again, this will be a preview of the result that can be obtained at the end.
Save the L image and close it.

Now for each R,G,B series, start a Preprocessing to obtain the master R,G,B images. Use Trichromy to create the RGB image, don't care for the color correction during this phase.
On the RGB image, you can now apply filters and color correction, don't look for sharpness here, and don't be worried too much about noise.

Reopen the L image, Align the RGB to the L (menu "Image/Align", if they have different size you may use Coregister), then launch LRGB combine. If you feel that the RGB added some color noise to the final image, delete the result, apply a low-pass filter to the RGB and repeat. Blurring in the RGB will not affect the sharpness of the LRGB result.

dredger
Posts: 8
Joined: 31 Jan 2019, 01:47

Re: After Preprocessing, How to Use Trichromy?

Post by dredger » 12 May 2021, 13:56

Thank you for this response. I followed this procedure and it improved my image (M51) considerably.

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