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M101 (no color)

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#1 JosephATL

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Posted 13 April 2021 - 08:28 PM

So, I recently snagged myself a Celestron deluxe OAG and got it working after some spacing issues.

 

This is at the full 2,000mm focal length with 2x2 bin, and no crop.  I'm reasonalby happy with how sharp the image came out, but I can't seem to bring out the colors, no matter what I try doing in Gimp.  Any tips on how to bring out the color?

 

 

Celestron C8 Orange Tube

EQ6-R Pro

Celestron OAG w/ZWO 462 MC guidecam

QHY 268C; Gain 100; Offset 18

48 frames at 80s each (1hr 4m)

APT for image capture. DSS and GIMP for processing.

 

 

Attached Thumbnails

  • M101_MQ.jpg

Edited by JosephATL, 13 April 2021 - 08:28 PM.

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#2 Astrolamb

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Posted 13 April 2021 - 08:33 PM

If you share the tiff or fits file I would be happy to give it a go in GIMP.



#3 JosephATL

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Posted 13 April 2021 - 08:54 PM

It's here:

 

https://drive.google...SGB?usp=sharing

 

Have fun with this one.



#4 Benschop

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Posted 13 April 2021 - 09:41 PM

Some good data there. One recommendation - shoot flat frames. They are very easy to take, and will eliminate the bright center / dark edges/ corners.



#5 Astrolamb

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Posted 13 April 2021 - 10:36 PM

Was the stack you have in your dropbox edited in any way? 

Do you have DSS set for "RGB Background Channel Calibration" or "Per Channel Background Calibration"? 

Do you have the option for DSS to "Align Channels in final image" checked? 

Was this an autosave from DSS with the post stacking stretch embedded? 

 

The reason I ask is because I did not have to stretch it at all and not only that, the RGB channels were aligned perfectly already. The histogram also looked really odd upon opening it up, its far more jagged than I any stacked image I have seen. It looked like a histogram for a layer where I did a "despeckle".... 

 

So anyway, I could have definitely spent more time here trying to get better detail and keeping the stars in good shape but I tried to be somewhat quick about it. I won't lie though it was a bit of a weird one. 

I definitely could be wrong here but I really feel like it is overexposed, the stars had very little color at all and most of them seemed like they were blown out. Besides that it really is great detail on the galaxy itself, I only sharpened it a little for my own satisfaction. Other than that I worked on pulling that color out of the hidden depths of your stack. 

 

Here is what I was able to manage. There is definitely color there I can promise you that, and this was only edited with gimp.

 

M101 C8 STACKONLY


#6 JosephATL

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Posted 13 April 2021 - 11:52 PM

Thanks!

This was saved immediately after the stack. No stretching, nothing.

My best guess as to why I wasn't getting any color is that I used too much gain and the dynamic range dropped off. The idea about some wrong with the stack settings in DSS has me itching to try reprocessing the data.
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#7 Astrolamb

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Posted 14 April 2021 - 12:01 AM

I played a little more and really found the fastest way you can bring the color back out. 

After you subtract your background,

1 go into the "colors" drop down

2 go down to "components" and select "channel mixer" from components

3 bring up the "blue in the blue channel" to 2.0

4 bring the "red in the red channel" to about 1.4

5 bring the "green in the green channel" to about 1.3

6 press okay

7 go into the "colors" drop down and open "saturation"

8 move the saturation to about 3 or 4. 

 

Voila, you have color! 

You can change the values to taste, but that gives you an idea of what to play with to bring the color forward out of the channels. 

 

I will mention that you need to boost your blue first, then balance in the red to get about the right amount in there, then balance in your green to bring the stars back to a white color and the core of the galaxy to a golden color. There may not technically be any discernable green in galaxies but the green channel does a lot of work in giving the image depth in its details. 

If you boost saturation before you make alterations in the channel mixer you will have some odd results. Try to only boost the saturation after you have tweaked the channel mixer to your liking. If you didn't do enough green after you saturate, undo the saturation and channel mixer and add more green, then redo the saturation. 

 

One last note, you can  bring the colors forward a little more by going into the "colors" drop down and selecting "hue-chroma" and boosting the chroma level. A little goes a long way with the chroma and I suggest you do it on a masked layer to keep the background under control. 



#8 Astrolamb

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Posted 14 April 2021 - 12:14 AM

Thanks!

This was saved immediately after the stack. No stretching, nothing.

My best guess as to why I wasn't getting any color is that I used too much gain and the dynamic range dropped off. The idea about some wrong with the stack settings in DSS has me itching to try reprocessing the data.

 

I can't blame you there! I tend to go through mine far more than I should, but it only helps me learn more about post processing at the end of the day. 

Give my suggestion a try too before you reprocess the data, but I wouldn't be surprised if one of those settings in DSS threw off the colors. I really have a pretty strong feeling that it aligned the RGB channels after stacking and its possible that it also set to "RGB background channel calibration" instead of "per channel background calibration".  One last thing to check when you are going through it is the  "RAW/FITS DDP Settings..." the Brightness setting under color adjustment should be set to 1 when you are stacking. I do it for both the RAW and FITS settings just in case even though I am only using RAW files with DSS. While you are in there you might as well go through them all to make sure everything else is right. 

 

If your gonna go through it all you might as well check all the boxes on your way through! smash.gif




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