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#1 rboone2020

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Posted 11 September 2013 - 09:36 AM

Folks,

My post may be similar to a recent one asking about M31, but I am seeking more general advice than is being addressed there. I am interested in what I may be missing in the process. I feel as if I am finally getting better at capturing light. My efforts may now need to shift to improving processing.

A few nights ago I imaged almost 3 hours of M31, with my new focal reducer giving me F6.3. I used an unmodded Canon T3i (600D). I was doing 10 minute subs (that's fun to say ... guide scopes are great!). I stacked the work in Deep Sky Stacker, and have experimented with its various color calibration. But in general, the red, green, and blue signatures seem highly correlated - everything is shades of grey.

Posted Image

Is the short answer "learn more about processing" (e.g., the extended demo posted on the other thread I have yet to watch), "capture more light", "use filters", or something else I haven't considered?

Thanks once again. Always appreciate the help.

Randy

#2 Madratter

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Posted 11 September 2013 - 10:53 AM

Color in in galaxies is very muted. It has to be brought out through processing. There are various ways of doing that and it depends heavily on the software you are using for your processing.

#3 rboone2020

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Posted 12 September 2013 - 08:59 PM

OK, thanks Madratter. I'll move forward then working with these images. I'll see if I can pull out more color.

#4 Ranger Tim

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Posted 12 September 2013 - 10:35 PM

Don't rely on DSS to do color balance for you. Other software does a much better job. Select "Use RGB background calibration" in the pop-up before the stacking takes place. Don't stretch the image too much and clip the ends of the histogram. If you need to balance the color open "levels" in a photoshop type tool and align the RGB histograms one at a time by moving the black point until they fall in line with each other.

Getting the most out of an unmodded DSLR is the same as a modded one. Here is a pic from early in my AP experience with an unmodded Nikon D50:

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#5 Ranger Tim

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Posted 12 September 2013 - 10:44 PM

The picture is nice but the star color is totally lost. Notice the rainbows in the star spikes? They should be much more prominent. I clipped the black point and blew out the stars in order to achieve a dark background with maximum stretch. I know better now. Hmmm, I need to go back to that stacked image and redo it!

Finally, don't expect deep color from an image that has been processed with an eye to revealing very faint details. Pulling DSO's out of the background often hurts the overall color and it is difficult to preserve it without increasing noise. Get yourself a dedicated astro post-processing program pronto. Lots of alliteration there!

#6 rboone2020

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Posted 13 September 2013 - 09:06 AM

Thanks for the info and demo, Tim. A nice image indeed.

An offhand question ... I've had a chance now to check out the extended demo that Shawnhar posted on another thread.
http://www.myastrono...31-Walkthrough/
And it is great stuff. I'm going to see what I can do with the images I have. They have severe stripping, but I'll ignore that for now and work on that another day; one step at a time. One part from the video isn't clear to me - I know the steps but would like an intuitive understanding.

In the step where he increases saturation, the author creates a "normal layer", a "soft blend" layer, and a "luminosity" layer. Only the blending modes on the layers are changed, no manipulation of the layers. The author then merges the three layers. Do folks have a feel for what is going on there? Why does that work?

Thanks,
Randy

#7 Stelios

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Posted 13 September 2013 - 05:19 PM

The star color may be lost, but from an artistic point of view, this is a symphony in navy blues. I love it.

#8 Ranger Tim

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Posted 15 September 2013 - 04:43 PM

One technique for saturating color without blowing out the highlights is to do an LAB color trick:

1) Flatten the file if it has layers. Of course, make a copy so you're not working on the original.

2) Convert to LAB color from RGB under the adjustments menu.

3) Choose the levels tool and click to work on "Channel A."

4) Enter a value such as 40 in the first box, then skip to the third box and enter the remainder to add up to 255 (in this case 215).

5) do the same for "Channel B."

Compare by clicking the review toggle. Add more color by closing Levels and opening it again, then repeating the operation. Choose the amount according to taste.

6) Convert back to RGB. This technique does not work on the luminance channel. Thanks to Anna Morris for this one!






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