Deep Sky Stacker Settings for Astrophotography
Choosing the right Deep Sky Stacker settings can make a noticeable difference when processing your precious data. With so much time and effort going into your capturing sessions outside, the least you can do is give yourself the best results possible when stacking! I use Deep Sky Stacker to stack and register all of my astrophotography images. Download DeepSkyStacker for free.
I’ve been using DeepSkyStacker for a few years now, and I’ve stacked images created by both a DSLR and a CCD Camera. Whether you are stacking .RAW image files from a Canon camera, or .FIT files from an ASI071 CCD camera, the right settings can be the difference between a good image, and a great one.
Choosing the right settings for DeepSkyStacker
For me, I’ve had most of my success using trial and error. For example, I was able to produce an image with the correct color balance using a CCD camera with an RGGB Bayer pattern. I discovered this during my Markarian’s Chain imaging session, by using a specific color adjustment setting.
Here’s the good news, generally the default settings work best.
I have experimented with many different combinations of options for stacking DSLR raw files, and have found that most of the default settings work best. There are a few things to keep in mind, but I have introduced more problems to my images than enhancements by changing the settings.
Stacking images from multiple nights
I regularly capture images on the same deep-sky object over multiple nights to increase the signal-to-noise ratio. I shoot through heavy light pollution in my backyard, which means I need to capture up to 4x or more the amount of exposure time someone living under dark skies would. Jerry Lodriguss has explained the process of compensating for brighter skies with added exposure time on Sky and Telescope.
All of this exposure time is great, but how do you properly combine it all?
Below: The Rosette Nebula processed using Deep Sky Stacker and Adobe Photoshop
Deep Sky Stacker Settings
If you follow my astrophotography tutorials, you will have captured light frames, dark frames, flat frames and offset/bias frames during each of your imaging sessions. These support files will go a long way towards improving your final image. I recommend capturing new support files for each night, rather than using previously captured data.
Only stack your best images
Before opening the files in Deep Sky Stacker, I pre-qualify the images I want to stack. I use a RAW image preview application called Adobe Bridge to review and organize my images. Any photos with football-shaped stars from hiccups in autoguiding are tossed in the recycling bin. The same goes for frames with airplanes, satellites or passing clouds.
What about .FIT files created be a CCD camera? These files can be hard to preview, due to the fact that they need to be debayed first. For this file type, I inspect and remove poor quality frames within DeepSkyStacker itself. This method can be a bit tedious, but a necessary step to ensure your final image only includes the best data.
In the DeepSkyStacker 3.3.4 settings, you are able to choose “Select the best 80% pictures and stack them“. I am not totally sure what the scoring process is by DSS, and I wouldn’t rely on this system to separate my good image frames from the bad. I still pre-approve all sub frames by loading them in.
If you have a better way to preview .FIT files, or a reliable way for DeepSkyStacker to score the best images, please let me know on Facebook.
Organize your images into 4 folders. Lights, Darks, Flats and Offset/Bias.
In the Main Group:
Open Picture Files
Select all of your light frames from your first night of imaging. Since you have already reviewed and approved all of the images in this folder, this is simply a matter of selecting every RAW file in your light frame folder.
Select the dark frames you captured from the same imaging session. The images need to be the same exposure length, ISO and temperature as your light frames. These can be easily captured with the lens cap on your camera. I recommend using a minimum of 15 dark files or more.
Here’s an example of the Andromeda Galaxy, stacked using only Dark frames. This image would have been much easier to process had I taken the time to collect flat and bias frames.
Flats require a little more effort than dark frames but can be collected in a very short amount of time. Stretch a white t-shirt over the objective of your telescope, and smooth out all of the folds. Shine an evenly lit bright light at the telescope objective, and capture a number of shots with your DSLR set to AV mode. 15 flat files can make a significant improvement to your final image.
Offset/bias files are quick and simple to capture. Just take 15 exposures with the lens cap on your DLSR. These exposures need to be the fastest possible shutter speed using the same ISO as your light frames. (On the Canon 450D, that’s a 1/4000 second exposure)
Use the tabs for stacking images from multiple nights
Once you’ve got your picture files (lights) and all of your support files loaded into the main group, it’s time to load up your files from night 2. Click on the small Group 1 tab at the bottom left of the screen, and repeat the process for opening files from imaging night 2.
Remember, you can stack different variations of exposures together in Deep Sky Stacker. This means a range of ISO sensitivity and exposure length.
Some imaging sessions may include all 3 supports files to compliment the light frames, some may not. This is fine. After all of the image files have been loaded into their respective categories, it is time to register and stack the frames into a single file. Finally, make sure to click “‘check all“, to make sure that all of the frames you have loaded are selected.
Before we click Register and Stack images, let’s take a look at the current default settings.
Accessing the Register and Stacking settings is accessible by clicking “Settings…” under the options tab.
The default Deep Sky Stacker settings for registering is set to a 10% star detection threshold. In my experience, the default value of 10% has worked very well for stacking images captured using my 12MP Canon 450D. If you decrease the star detection threshold, deep sky stacker will detect fainter stars. The number of stars in a given light frame is displayed in the lower half of the screen. With a light frame selected, look for the #Stars category.
The following checkboxes should be checked before moving hitting “OK”, and letting deep sky stacker begin its process.
- Register already registered pictures
- Automatic detection of hot pixels
- Stack after registering
The Deep Sky Stacker website states that the automatic detection of hot pixels only works if using Super-pixel, Bayer Drizzle, bilinear and AHD interpolation modes. However, I leave this box checked regardless and hot-pixels and stacking errors have never been an issue.
Unless you are experiencing errors in the stacking process, leave all of the values in the stacking parameter dialogue box unchanged. Yes, this sounds like a conveniently simple option, but default values are usually set for a reason! If you want, go ahead and click on the different modes in the “Result” tab. Deep sky stacker will show you a preview of the final composure created using Mosiac and Intersection modes.
I prefer to use Adobe Photoshop for the final framing and cropping of the image.
As for the stacking parameters of the light and dark frames, Kappa-Sigma clipping and Median work well in the Light, Dark, Flat and Bias/Offset categories. I do not use any additional features such as the detection and cleaning of hot pixels in the Cosmetic tab.
One setting I do change, however, is the output location folder of the Autosave.tif file. I prefer that these images populate in a specific folder of my choice rather than mixed in with a folder of light frames.
Depending on the quality of and amount of light frames available, I usually select the best 80-90% of pictures and stack them.
Ready to Stack?
You’ve got all of your lights, darks, flats and offset/bias frames loaded. The default settings are currently selected, and the ever-comforting green bar is displayed (confirming your use of all support files) But wait, if only there was a way to confirm all of the files are as they should be.
The Stacking Steps Window
Before you run DSS, be sure to check and see if there are any warnings in the dialogue window. In the case above, there was a single Flat frame with a miss-matched ISO speed. These warnings are useful for catching little mistakes in your file organization that can potentially make a big impact on your image.
At this point, you can remove or add any frames based on the information Deep sky stacker has provided.
If all looks well, and there are no more warning messages in the Stacking Steps window, you can proceed to run Deep Sky Stacker. I enjoy the information preview about the estimated total exposure time.
Processing the final image created by Deep Sky Stacker
In the video tutorial below, I walk through some of the basic settings used in Deep Sky Stacker. I then bring the image into Adobe Photoshop for further image processing.
When Deep Sky Stacker has completed its process of registering and stacking all of the image frames together, a preview of the constructed Autosave.tif file is displayed onscreen. Based on the design of this software, you would think that the next logical step would be to make adjustments in the RGB/K Levels, Luminance, and Saturation area.
If you plan on processing your image in Adobe Photoshop, I recommend leaving these settings as they are.
Balancing levels, curve adjustments, and boosting saturation are all staples of an Astrophotography processing workflow in Adobe Photoshop. Photoshop offers many more options and a higher level of control than Deep Sky Stacker for such edits.
What about the Recommended Settings option?
Deep Sky Stacker has a “Recommended Settings” option that offers suggestions based on the image files submitted. Some of the recommendations include changing the stacking mode used such as “Use Median Combination Method”.
I have tested both the recommended settings and the default settings and found the default to produce better results.
If you are determined to see the subtle differences in the final stacked image, you can go through the entire process using the default Deep Sky Stacker settings vs. the recommended settings. I found that the recommended settings had varying results, with fuzzier more washed-out stars than the original stack. I prefer to try both stacking methods and compare the results on a per-image basis. You may find that the stacking modes suggested by DSS improve your image.
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