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Thread: Step-by-step processing example (NGC 891)

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    Default Step-by-step processing example (NGC 891)



    Thought I'd list out my step-by-step processing workflow. Maybe some people can learn something, and some people can teach me something at the same time.

    I shot 4.5 hours of NGC 891. Calibrated and stacked with darks, flats, and offsets in DSS. Saved as 16-bit TIFF with "Embed adjustments" setting.

    This is what it looked like upon opening in Photoshop:


    First step was to select four points using the color picker tool.
    Point
    1. 1 was what I expected/wanted to be completely white.
    2. Point 2 was what I expected/wanted to be completely black.
    3. Point 3 was one spot I wanted to keep my eye on - the dust lane in the center.
    4. Point 4 was one spot I wanted to keep my eye on - the glow from the galaxy's disk.


    Looking at point 1 (supposed to be white), I noticed that the color values were not at 255, 255, 255. So using a Levels adjustment layer, I moved the white point for each of the R, G, B channels to get point 1 to 255, 255, 255.


    Next, I needed to adjust the mid-tones. So I added a Curves adjustment layer, where I pulled the curves a little left of the midpoint up (input 80, output 255). I chose these values by two criteria: (1) what looked good (in terms of lightening the image to see more detail, but (2) still kept all points (except for point 1) at less than 255, 255, 255. If any of points 2, 3, or 4 hit 255, 255, 255, then that would mean that I'd moved the curve too much and would need to back down.


    Depending on how much the Curves adjustment worked, I will often do another Levels adjustment and move only the gray point to lighten the mid-tones further. But in this case, the Curves adjustment did enough, so I didn't do any more Levels for the mid-tones.

    Now the image shows a lot of the faint detail, but everything is light and little contrast. So I added another Levels adjustment layer. My goal was to darken the background to add contrast. So I picked the black point eye-dropper in the Levels dialog box (in lower right) and clicked on a part of the image that I wanted to represent the black point (dark area in lower right in this case). This automatically adjusts the black points in the RGB channels to set that point to 0,0,0.


    This darkened the background, but the galaxy details are still very dim. So using the same Levels dialog box, this time I picked the white point eye-dropper and clicked on a point in the image that I wanted to be white. I picked a point right on the edge of the bright star just on the edge of the galaxy's disk (left of center). Clicking in the middle of the star would not have made any difference, since that point is already fully white. This step takes some trial and error to get the right look. Again, I kept one eye on the color values of the three points (2, 3, 4) to make sure they didn't turn to all white (255, 255, 255).


    At this point, the image is looking pretty close to a final version. However, there is still a lot of noise. My next step is to do some noise reduction. Instead of reducing the noise of the final image with all the above adjustments, I want to make the NR adjustment at the most basic level, i.e. the raw image before any adjustments. Since I've made all the above adjustments using adjustment layers, I still have the original raw image. So I select that background layer and apply Noise Ninja (using auto-profile settings). This smooths out the image a lot.


    Last step is to apply the Local Contrast Enhancement adjustment from Carboni's Astronomy Actions. This adds a bit more contrast (darkens the dust lane).


    That was it. In this case, I didn't need to do any selective adjustments or layer masks, but it would be pretty easy to do since adjustment layers automatically allow the application of masks.

    Here's a comparison of the image from when I opened it to when I finished it:


    And this is the final image:


    Any comments, critiques, questions welcome.
    Visual: Celestron NexStar 8SE
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    Great step-by-step manual, very thoughtful workflow. Photoshop is a great instrument for photography, astrophotography included. Very similar workflow would be with GIMP - with some extra steps and workarounds maybe. And all the process would look much shorter in Lightroom with it's dedicated photography interface. For someone who would like to try it : digital photography techniques | Adobe Photoshop Lightroom 3
    Still, great manual. I've got it printed and put together with my other photo manuals.
    Thanks!
    Last edited by mplanet62; 09-17-2010 at 11:12 PM.

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    Simply amazing!

    I didn't understand all of it, but I've got a place to start. I'm going to see if I can do that with some of my wide view shots.
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    fuzz: great stuff as usual. Image is outstanding and the explanation is something we can all use to help us bring out the details. Thanks for this.
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    Quote Originally Posted by mplanet62 View Post
    And all the process would look much shorter in Lightroom with it's dedicated photography interface. For someone who would like to try it : digital photography techniques | Adobe Photoshop Lightroom 3
    I love Lightroom and use it for 90% of my regular/non-astro image processing. But for the fine-tuned processing required for astrophotography, I'm not sure how well it would work.

    The weaknesses I see with Lightroom for AP processing:
    • No way to track color values for specific points throughout processing.
    • All changes are cumulative. In PS, with adjustment layers, I can easily turn certain adjustments on and off and change them as needed, no matter what order I applied them in.
    • No layer masks. In PS, I can create multiple masks, save them, and use them as many times as needed.


    There may be workarounds in LR for the above issues, but I haven't found them -- but would love to know them if anyone has. Also, for simpler images (like this one) which don't require fine-tuned processing, LR will probably work. mplanet62, have you used LR for astro processing? How do you like it for that specifically?

    I did try LR on some astro-images, but found that for the most part, I was making adjustments on a trial-and-error basis. With PS, I can use the color values for the four points I set to know exactly what I need to do and have an idea of what will happen with each adjustment. For me at least, PS takes a lot of the guesswork out.
    Visual: Celestron NexStar 8SE
    Imaging: Astro-Tech AT6RC, Sirius EQ-G mount, Orion autoguider, Canon 40D
    Location: Colorado Rockies

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    I want to put a "thanks" on Fuzz's post but the Thanks button is offscreen !!

    Anyway, that is very informative. I notice you have some plugins for astronomical image processing...would you mind describing them and what they do?


    (Is that a new supernova in there, near the core, right on the centerline of the dust lane?...wouldn't that be exciting? Several supernovae have been detected in this galaxy already...)

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    Quote Originally Posted by alsetalokin View Post
    I want to put a "thanks" on Fuzz's post but the Thanks button is offscreen !!
    Yeah, sorry, I didn't have time to create smaller versions of the images to put in the post with links to the larger versions.

    I notice you have some plugins for astronomical image processing...would you mind describing them and what they do?
    It is actually one set of plugins, Carboni's Astronomy Actions. It's $22, and has about 30 astro-specific actions. More details here: Astronomy Tools Action Set by ProDigital Software. I use the Local Contrast Enhancement on almost all astro-images -- helps create more contrast in nebulae and galaxies. Some of the other ones I use with problematic images, where nothing I do seems to get it right.

    (Is that a new supernova in there, near the core, right on the centerline of the dust lane?...wouldn't that be exciting? Several supernovae have been detected in this galaxy already...)
    It is very prominent, isn't it? I'm guessing it is a Milky Way star in the foreground. Because you're right, the only way a star from that galaxy would be visible is if it were a supernova, but in that case, we'd probably have heard of it.
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    Thanks for this Fuzz I will try to process my M31 again using your method, and possibly using flats as well at ISO 100
    cheers!
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    Quote Originally Posted by Fuzz View Post
    I love Lightroom and use it for 90% of my regular/non-astro image processing. But for the fine-tuned processing required for astrophotography, I'm not sure how well it would work.

    The weaknesses I see with Lightroom for AP processing:
    • No way to track color values for specific points throughout processing.
    • All changes are cumulative. In PS, with adjustment layers, I can easily turn certain adjustments on and off and change them as needed, no matter what order I applied them in.
    • No layer masks. In PS, I can create multiple masks, save them, and use them as many times as needed.


    There may be workarounds in LR for the above issues, but I haven't found them -- but would love to know them if anyone has. Also, for simpler images (like this one) which don't require fine-tuned processing, LR will probably work. mplanet62, have you used LR for astro processing? How do you like it for that specifically?

    I did try LR on some astro-images, but found that for the most part, I was making adjustments on a trial-and-error basis. With PS, I can use the color values for the four points I set to know exactly what I need to do and have an idea of what will happen with each adjustment. For me at least, PS takes a lot of the guesswork out.
    Yep, the Lightroom does not have the full grunt of PS. Specifically, its inability to work with layers makes it more editor than creative instrument. However, it may be very useful for doing some simpler work - just as you said. And it's much quicker to do this sort of job in LR - just by pulling or squeesing the histogram for example.The workflow you have described needs some serious skill to follow. LR limits the capabilities, but makes it simpler and more "visual" at a lower level of astro photography expertise - which I honestly do belong to. Also, it's simpler to see the frame's development potential before proceeding to PS - which can be started from Lightroom - must be quite useful for DSLR phography. I see what you say about cumulativity of Lightroom processing - it's possible to cancel some change, but reapplying it in different sequence gives you different effect. True.
    As for my experience with Lightroom - I found it quite useful processing night sky photos taken from a tripod or piggyback. Also, Moon shots. At the moment I'm trying to drift away from LR - I've found that it was not giving the best result with my camera's RAW. I shoot RAW these days - I'm sure you know the trouble. At the moment GIMP is my editor of choice - it's free and works with both Windows and Ubuntu on my double-system comp.
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    Last edited by mplanet62; 09-18-2010 at 09:52 AM.

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    Thank you Fuzz.
    Can someone please translate this excellent step-by-step tutorial to Gimp (all steps please)?
    Thank you.

 

 
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