Tag Archives: noise reduction

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.

Stacker’s Checklist

Created November 2, 2010
Last Updated April 19, 2019

Note: Items in RED are suggestions that apply in particular to star trail captures and may be changed based on circumstances at the scene and goals.

Site Selection

  • Sunrise, Sunset, Moonrise, Moonset and moon phase all known.
  • Safe area, travel paths known


  • Camera, tripod, release plate, camera batteries, memory card, lens, intervalometer + batteries, lens hood, rain protection, headlamp, flashlight/torch, and items for light painting.

On Site

  • Tripod set up – no leaning (center column should be vertical) – leg locks tightened.
  • Camera aimed, leveled.
  • Camera locked onto tripod. Head tightened.
  • Tripod weighted/secure and everything is wobble free. Keep the tripod low and out of the wind for best stability. Do not extend the center column.
  • Neck strap removed or secured to prevent wind throw. Intervalometer and any other cord, or wiring also secure. Velcro on the intervalometer and the tripod leg is a handy trick.
  • Save GPS coordinates and/or mark site with glow stick / other?

Camera Settings

  • Manual Mode, Bulb exposure
  • ISO 200  (varies but from 100 to 800, and up to 6400 if capturing meteors or the Milky Way)
  • Single Exposure
  • LCD brightness down
  • Image review time off
  • Record in RAW
  • White Balance = daylight (Auto not recommended)
  • Aperture f/4 (f/1.4 to f/7.1)
  • Auto focus OFF
  • Image stabilizer (vibration reduction) OFF
  • Long Exposure Noise Reduction OFF
  • Mirror Lockup OFF
  • Auto Exposure Bracketing OFF
  • Focus Assist OFF (this often fires an infra-red beam/red beam and will annoy other photographers). On many cameras this feature is on the flash unit/speedlite. On Nikons, this resource may help.

Timer Setup & Test

  • No delay, length of exposure = 1:59 minutes (adjust based on conditions. A 2 minute total interval is a good starting point), interval = 1 second, Num exposures >= 120
  • Timer cabled to camera
  • Test sequence (lens cap on) – Verify that second shot starts before canceling.

Focus & Final Framing

  • Check image composition, field of view.
  • Set camera to Aperture priority mode (not needed if it is already dark)
  • Take several bracketed shots in daylight or twilight: if it is already dark take a high ISO “range finding” shot. E.g. 2000 ISO for 30 seconds.
  • Pixel peep and adjust focus until sharp.

Battery and Card Shuffle

  • Remove memory card and insert second card. Format new card in camera.
  • Take second set of bracketed shots.
  • Return camera to Manual/Bulb mode.
  • Turn off camera and remove battery.
  • Reinsert battery (or insert fresh battery).
  • Verify that all settings are correct (See Camera Settings, above)

Final Steps

  • Check for wobble. Start by lightly jostling the camera, tripod, center column and even walking around in the area to make sure no movement occurs.
  • Set DELAY on interval timer appropriately (at least 5 seconds).  Goal is to start and/or end in twilight.
  • Secure cables for timer, external batteries (and neck strap). Do not block battery or memory card access.
  • Switch to aperture priority mode (so that your manual settings do not change), take a single image and re-verify focus. If already dark, take a high-ISO range finding shot for this task.
  • Switch back to Manual/Bulb.
  • Verify all camera settings as described in Camera Settings
  • Start Timer and verify that the timer is running.
  • If practical wait for first two shots to complete.
  • NOTE: You can leave the lens cap on for the first few exposure to collect DARK frames.

My thanks to Mike W. for comments and improvements to this checklist.

Additional References

(Mostly) Free Tools for Star Trails and Star Circles

Planning Tools


  • There are lots of resources for weather, but I prefer ones that predict a few days in advance and provide an hour-by-hour forecast. In that category, I find Wunderground.com to be the best for multi-day forecasts. Wunderground’s forecasts include the temperature, wind speed and direction, percentage of cloud cover, probability of precipitation and the dew point throughout the day. And the “wundermap” of IR and visible radar is a great help, too – it even includes nearby weather stations, and webcams where available.
  • It is hard to beat ClearSkyChart – if there is a nearby astronomy observing area, that is – for predictions for the next 36 hours.  It is a little “busy” to see a Clear Sky chart, but once it is understood it is a great tool. Hint: Darker everything is good.

Location & Celestial Alignments

There are many online communities for finding and discussing photo locations.  I explain one method I use for finding photogenic locations in the video below.

  • The Photographer’s Ephemeris – free (and priceless!). Knowing the moon phase as well as the rise and set times of the sun, and moon is very helpful. I use a variety of tools for this, but TPE is the most useful by far- and there is an iPhone version as well (which is more difficult to use than the desktop version,  unfortunately). Below is a video demonstrating how I use TPE.
  • Sun and Moon Data (Monthly Calendar) – free (web resource). Knowing when the brightest lights in the sky will rise and set, and when twilight occurs is very important. Even better still, is this resource for printing out the vital data for an entire month.

Image Tools

Photo Management

  • Picasa3

It is hard to beat Picasa3 for a quality tool that works on Windows and Mac. The tool includes keyword searches, galleries, organization in albums and/or by folders and much more. Picasa3 is JPEG centric but it does recognize almost all formats – including RAW, and keeps the original files so that destructive edits are not so destructive.  I use it mostly for displaying and selecting photos, exporting them and uploading them to Flickr with the Flickr upload plugin. To use the Flickr Uploader plugin, the Flickr Uploadr tool is needed.  Other features of Picasa3 that I find very useful are the “CD Burn”, the Movie Creator, and the Text tool.  The image straightener tool is the simplest, cleanest method for fixing tilted horizons. I also use the export feature to add my copyright onto downsized images for export to Flickr or other sites.  Picasa3 does SO much more as well. And it is free! Free, I tell ‘ya!

  • Lightroom

I have no experience with Lightroom. I can’t bring myself to pay $200 for something Picasa3 already does very well and for free – and especially after shelling out mucho dinero for Photoshop.

Stacking (Combining) Images

For Windows based machines:

  • Image Stacker by Tawbaware – at $17 this is easily my favorite because of its versatility and speed. It is also well supported by Max Lyons. I highly recommend it.  Look below for a tutorial.
  • Startrails.exe – free. English and German versions. No updates in many years and it has a few “issues”. Hard to beat the price, though! It does handle dark frames better than Image Stacker. The tutorial below also shows startrails.exe.

For multiple computer types – including PC and Macintosh

  • DeepSkyStacker – free. Hard core tool for astrophotography and not particularly useful for star trails.
  • PixInsight – 171 euros. No experience. Looks daunting and again, geared toward astrophotography rather than star trails.
  • Adobe Photoshop – ($varies). The Extended version Statistic script is handy for stacking. Otherwise it is a tedious and slow tool (IMHO) for stacking.
  • GIMP – free. An open, free alternative to Photoshop. Trying to assemble all of the plugins and prerequisites to get the tool to do stacking is not worth the effort. GIMP under the covers is also an 8-bit per color editor so loses some fidelity. On the other hand, I find GIMP much, much easier to use for typical masking and combining of images.
  • Picasa3 – free. Yes, even Picasa3 can stack images using a “collage” in “Multi-exposure” mode. But the results are not all that spectacular. A plugin for Picasa3 could make nearly all the other tools unnecessary.

For a tutorial on using Image Stacker and/or StarTrails.exe please see here:




I can usually load Picasa3 make my simple adjustment and save the file before Photoshop has finished loading itself and an image.

  • Picasa3 – free. Very easy and fast to do simple spot touch ups, color balance, horizon corrections and tonal adjustments.
  • Photoshop – ($varies). More complicated adjustments like removing aircraft trails, combining images (hand HDR) are better left to Photoshop.

Image Manipulation

  • Photoshop – ($varies). The swiss army knife, atomic weapon, and grapefruit spoon of photo manipulation.
  • GIMP – free. In many ways easier to use then PS.
  • FSResizer – resize, frame, add copyright information.  A specialty tool, but a quick and handy one.