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Astrophotography and Sketching >> DSLR & Digital Camera Astro Imaging & Processing

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akulapanam
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Reged: 08/27/12

Re: Achieving color in galaxy shots new [Re: Dave Venne]
      #5674846 - 02/11/13 09:40 PM

Those are looking better. I'm still not sure why DSS is suppressing the color so much compared with the imagesplus stack. I'm going to try and get a free trial and compare the results with 200+ frames.

No clue on the vertical banding I have never had that problem before.


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srosenfraz
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Reged: 03/06/11

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Re: Achieving color in galaxy shots new [Re: akulapanam]
      #5676845 - 02/13/13 12:01 AM

Quote:

Scott if you don't mind try this file out and see if you can do anything with it. It is looking a little better to me. I used imagemagick to get around the dss saving issue and I switched dss to standard mode from mosaic. The mode shouldn't make a difference but it might help.

http://sdrv.ms/154NAcz





Sorry, I didn't have a chance to look at this until tonight. This file was easier to work with in that the blue color was inherently there. I enhanced it via Lab Color and Selective color adjusments, but I didn't have to force blue into it by stretching the blue channel (like I had to do with the earlier version). Here's my quick and dirty on it:



I posted my .psd file if it'll help you (40 MB).


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akulapanam
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Reged: 08/27/12

Re: Achieving color in galaxy shots new [Re: srosenfraz]
      #5676910 - 02/13/13 01:03 AM

Thank! That really does look much better. The key seems to be using imagemagik to take the autosave and convert it, really "unbox it", to 16 bit. I just downloaded your psd file and I'm going to try and learn how to do your processing routine.

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srosenfraz
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Re: Achieving color in galaxy shots [Re: akulapanam]
      #5676978 - 02/13/13 02:53 AM

Quote:

Thank! That really does look much better. The key seems to be using imagemagik to take the autosave and convert it, really "unbox it", to 16 bit. I just downloaded your psd file and I'm going to try and learn how to do your processing routine.




Glad to hear you may have found a better way convert it. Let me know if you need any explanation on the .psd file. I left it all as separate layers to show all steps, but you could flatten the file after each step or a group of steps. Good luck with it!


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akulapanam
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Reged: 08/27/12

Re: Achieving color in galaxy shots new [Re: srosenfraz]
      #5684038 - 02/16/13 06:38 PM

I have been reviewing what you did. The only area I'm having a hard time understanding is how you did the lab color b channel increase.

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srosenfraz
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Re: Achieving color in galaxy shots new [Re: akulapanam]
      #5684285 - 02/16/13 09:29 PM

Quote:

I have been reviewing what you did. The only area I'm having a hard time understanding is how you did the lab color b channel increase.




Here's my process for doing that:

1) Duplicate the image (Image | Duplicate)

2) Flatten the image (if it isn't flat).

3) Convert to Lab Color (Image | Mode | Lab Color)

4) Click on the Channels tab and the click on the b channel so that it is highlighted in blue. Then, click on the eyeball next to "Lab" so that all channels have eyeballs (Lab, lightness, a, and b). This makes it so that you see all the channels (i.e., the image looks normal), but you're only working on the b channel.

5) Increase the contrast (Image | Adjustment | Contrast). This is one of the few times that you want to use Contrast instead of curves. You are not increasing the contrast of the image - you are increasing the contrast of the b channel. The b channel affects blue and yellow. So, increasing the contrast in the b channel increases the saturation of blue and yellow. Increase the contrast (saturation) until you're satisfied with the result. If needed, you can do a second or third pass of increasing contrast to bring out even more color.

6) You can do the same thing with the a channel (increase the contrast). This increases the saturation of the green and magenta. Most astronomical images will have very little green (the general exception being planetary nebulae), so the effect of increasing the contrast on the a channel is to saturate magenta. This can be useful for bringing out Ha regions in galaxies or emission nebulae.

7) Once you're satisfied with your adjustments, click on the "Lab" channel. This should highlight all 4 channels (Lab, lightness, a, and b).

8) Copy the image to the clipboard (Edit | Select All; Edit | Copy).

9) Click back on the original image and then click on the Layers tab. Edit | Paste your Lab color adjusted image as a layer on top of the stack.


That's the basics. A couple of things to keep in mind with this:

a) Lab Color is good for many images, but keep in mind that you can't increase blue without increasing yellow (and, similarly magenta and green). So, while you're increasing the contrast in the b or a channel, keep an eye on both colors you're saturating to make sure that one doesn't become overpowering (i.e., if increasing the b channel makes your image look to yellow, its time to not increase it so much).

b) Oftentimes, you'll want to use Lab color for PART of an image and not the entire image. Using masks can be very effective in bringing out the color in just the areas you need.

Hope this helps.


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Tonk
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Reged: 08/19/04

Loc: Leeds, UK, 54N
Re: Achieving color in galaxy shots new [Re: srosenfraz]
      #5684653 - 02/17/13 05:41 AM

Quote:

astronomical images will have very little green (the general exception being planetary nebulae)




You have totally forgotten about comets - can be the greenest of all astro objects!


On colour saturation in general. The alternative to doing L*A*B colour treatment is Photoshops Match Colour tool. It isn't immediately obvious how to do this given the tool is actually designed to balance colour in one image to match another, but if you set it so the two (source and target)images are the same image then the colour saturation controls work superbly and avoids increasing chromatic noise etc while giving excellent colour enhancement from the midtones towards the highlights (my two recent comet postings use this technique)

Another trick is to use a Hue/Saturation layer to selectively desaturate precise colour ranges after a general saturation step. I set it to remove greens and magentas in stars after using a "match colour" saturation - though if your initial colour balance after debayering is good this desat step rarely has to be done.


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srosenfraz
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Re: Achieving color in galaxy shots new [Re: Tonk]
      #5684990 - 02/17/13 11:17 AM

Quote:

Quote:

astronomical images will have very little green (the general exception being planetary nebulae)




You have totally forgotten about comets - can be the greenest of all astro objects!







Whoops - you're absolutely right. My apologies to you and all the comet photographers. Sorry to have been a DSO snob.

:-)


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Tonk
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Reged: 08/19/04

Loc: Leeds, UK, 54N
Re: Achieving color in galaxy shots new [Re: srosenfraz]
      #5685045 - 02/17/13 11:53 AM



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