Simple Astro Processing Technique to Conquer Noise

Published: Jun 20, 2012
Last Updated: March 5, 2017

Is one of these your scenario?

  • It’s really dark. The ISO is bumped up, the noise is screaming at you, but you REALLY want the shot.
  • The Milky Way looks SO gorgeous, you want to take it home with you like a trophy, but when you shoot short enough exposures to prevent smears, mostly what you get is noise.
  • You are surprised that you can faintly make out the Milky Way. You know your buddies will be jealous if you can show them a photo of the Milky Way that you took from IN TOWN. They won’t believe you!
  • You have a great star trail, but your foreground is not lit. The photo would sing if you could tease out that foreground – minus the noise, of course.

In the Star Circle Academy’s “Astrophotography 101: Getting Started without Getting Soaked” webinar we cover all the theory and equipment you need to take gorgeous photos of deep sky objects (nebula, galaxies):

Colorful Neighbor

But absent the fancy equipment, all you need is a wee bit of Photoshop skill to get a pretty compelling image. Less than 10 miles away from Palo Alto, California, with over 8 million households in a 50 mile radius I got the image you see below. I understand why you might not believe me.  Is it the most compelling Milky Way you’ll ever see – definitely not.

Urban Milky Way [C_036919-23PSavg]

Here is the best I could do with a single image from the same location:

Milky Skyline [5_006550]

After much processing it’s still noisy (grainy) and contrast poor.

We covered the processing technique in our Night Photography 150: Photo Manipulation I Webinar – among many other topics. Below is a 7 minute video describing how to do that simple astro photography processing.

If you think a webinar on photo processing would be of interest, join our Interest List for this or other topics and you’ll be notified when we schedule the next webinar. You can influence the topics we choose to cover by making your comments here.

Simple Astro Photo Processing in Photoshop CS5 from Steven Christenson on Vimeo.

NOTE: If the above says password required, enter scanp150 In the video, you’ll also learn how to constrain the healing tool, use curves, layers, and the history tool to undo inadvertant changes.

ALSO NOTE: Advanced StackerPLUS has a built in averaging operation. You just feed it the images. It does NOT do auto alignment, however.

In our next installment, we will talk about how to get the Milky Way shots in the first place. Camera considerations, settings, tradeoffs.

By the way, this image consists of a single sky shot and a multi-processed foreground using the technique described above. Click the image for further details.

South Side Truckin' [C_009842]


We have another video tutorial that uses some similar processing techniques:

12 Minute Star Trail using Advanced Stacker PLUS version14D from Steven Christenson on Vimeo.

10 thoughts on “Simple Astro Processing Technique to Conquer Noise

  1. sathish

    Great tutorial.
    I never thought of auto-align images to align multiple exposures of Milky Way.
    I guess you learn something new everyday!

  2. Pingback: The Elusive Milky Way – Capture an Image | Star Circle Academy

  3. Juan

    I did once this kind of stacking in Deepskystacker. Did you ever try it? What’s your opinion of that software?

  4. Todd Walker


    Thanks for sharing the video above.. I have used this same PS stacking technique in the past on waterfall photography..not so much for noise-reduction reasons (because ISO 200 was used) but more to show that “silky” water look when I forgot my ND filter.

    You mentioned at end of the video on using a foreground in the Milky Way shot. In my experience the “Aligning” methods get real confused in doing so. I had tried to auto-align in PS as well as DeepSkyStacker but unless there are ONLY stars in the shot the software struggles (which is expected). Here’s where I’m at in deciding how to shoot a “static” star field with a foreground:

    1) Crank up the ISO and use a fast/wide lens (single shot)
    2) Attempt to align as best as the software can then “mask” in the separate foreground image, thus eliminating the “blurry” foreground.

    With method #1 I still find myself wondering if shooting a separate foreground shot as I need to “refocus” on the foreground and not the stars. If I don’t then the foreground could be blurry (knowing the lens Hyperfocal length would help perhaps…?). Is this rational thinking or even practical?

    With Method #2 again the masking can be a nightmare and the aligning is not the greatest with a foreground object. Maybe I just think too much…

    Anyhow, great stuff here Steve!

    1. Steven Christenson

      Autoalign doesn’t work with foreground elements and a rotating sky unless you remove the foreground.

      As for refocusing – that will make things much harder because changing focus usually makes small, but noticeable changes to the “zoom” or field of view. Unless your foreground is REALLY close and it’s important to get it in focus I find setting my camera at hyperfocal distance is just fine. In fact if I have to choose between an in-focus foreground and an in-focus sky, I’ll pick the foreground.

      Finally, Photoshop does know how to do focus stacking automatically – the problem is the exposures needed are so long that the sky moves and objects in the frame change.

      Combining a foreground and a background is not particularly difficult, in my opinion, if you’re careful to not allow anything to move:

      Cascade of Stars [C_049409+12]

      BUT here I’m using a SINGLE shot of the Milky Way from a high performing camera.


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