Stacking Night Landscapes With DSS

In this article I will present a simple way to use DeepSkyStacker, a free tool commonly used for astrophotography, to improve nightscapes.

Final Image Before and After Stacking

What to Improve

In night landscapes, if we want round stars, we must limit the exposure time to avoid trails. This means the shot will have some unavoidable level of noise. We can reduce the noise improving the signal to noise ratio using the technique known as Stacking. This is something done everyday in astrophotography and it can be used in exactly the same way to improve our landscapes.

The Theory Behind Stacking

The theory is very simple, in each shot noise makes the luminance value of each pixel fluctuate. If we take multiple shots and average the luminance value for each pixel across frames we can reduce noise. The more shots we take the more we can approach the real luminance value of a pixel.

Enter Deep Sky Stacker

Deep Sky Stacker is a free program that can align, calibrate and stack multiple shots as long as you have stars in them. DSS can do much more than what I present in this article, feel free to ask me if you need a hand diving into DSS features and different stacking methods.

And now it´s time to present the idea of this article

We are going to take the same shot ¨n¨times. In this example I took a photo of a rural road at night 10 times. Now we have to stack the shots and we have to stack them twice!

The reason is simple, the stars move due to the earth rotation but the ground features remain static, so if we align the stars the ground is blurred and if we align the ground the stars produce trails. So we´ll stack the shots twice.

DSS can work with RAW files but for landscapes I prefer to convert the RAW files to 16 bit Tiffs first. This allows me to set the WB, exposure compensation, saturation and contrast before stacking.

For The Stars

Load the Tiffs into DSS  (open picture files) and click ¨check all¨ to mark all the files. Then use ¨Stack Checked Pictures¨and click the ¨recommended settings¨ button to see what DSS recommends. Follow DSS wise advice and click the Ok button to stack.

The Sky, Before and After Stacking

DSS goes into deep trance and stacks all the frames de-rotating each one to make the stars fit. Once finished ignore what you see as the result, make sure the option ¨embed changes but don´t apply¨ is checked and save the file as a 16 bit Tiff. Name this ¨stacked_sky.tiff¨

For the Ground

To stack the ground we proceed in the same way but we need to stop DSS from aligning the stars. Click ¨Stack checked pictures¨, follow recommended settings. And then click ¨Stacking parameters¨and under the tab Alignment check ¨none¨. Then click OK and the frames will be stacked. Save the results as ¨stacked_ground.tiff¨

Ground before and after stacking

Blending Both Shots

We have now two shots, one with blurry ground and nice stars and one with nice ground and trailing stars. We just need to load both shots as layers in our favorite editor and use a layer mask to take  the sky from one stack and the ground from the other. If you are used to layers this is very simple. The result is a stacked shot where both the sky and the ground have a much better signal to noise ratio.

Final Remarks

This very simple tutorial presents an easy way to use DSS to stack night images, this can help reduce noise in an image not only improving the final result but also allowing a more aggressive processing of the image.  The less noise you have the more you can push the exposure and do other processing.

We used a single shot here but it’s very common to expose for the ground and the sky in different ways, even at different times, using different F number, ISO etc. Nothing changes, we still have two stacks and then we have to blend them together.

DSS is a powerful tool, it has many options and additional features that are used in astrophotography and we haven’t touched in this article.