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Astrophotography Stacking & Image Retouching Is Now Available In Affinity Photo

The inexpensive Affinity Photo photo editing software now has an Astrophotography stacking workspace which can be used to create breathtaking images of the night's sky. To learn more about this awesome new tool, take a look at this quick guide on stacking and editing astrophotography images in Affinity Photo.

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Rosette Nebula SHO |

Version 1.9 of Affinity Photo launched earlier this year in February and introduced an array of useful and powerful improvements, from linked layer functionality to better organisation for LUTs, OpenCL hardware acceleration for Windows and long-awaited saveable workspaces.


Introducing Astrophotography Stacking In Affinity

Flame And Horsehead Nebula HaRGB |
Flame And Horsehead Nebula HaRGB


One of the more esoteric additions was the introduction of a new ‘Persona' (or workspace) for astrophotography stacking. This functionality is not commonly found in image editors -  instead, it has always been the domain of dedicated astrophotography software, which can vary in price from free to several hundred dollars.

In this regard, Affinity Photo is relatively unique: it can perform the entire postproduction workflow required for professional-level astrophotography, all in 32-bit linear precision. The workflow is not complex either - if anything, the straightforward nature of the entire process may seem contradictory to expectations at first!


Astrophotography Stacking In An Inexpensive Photo Editor

Vela Supernova Remnant HaOIIIRGB |
Vela Supernova Remnant HaOIIIRGB


To understand the significance of having this functionality in a low-cost image editing application, we should consider the complexity of the stacking workflow and its requirements. We stack multiple exposures of the same subject to increase SNR (signal to noise ratio) - essentially, to reject noise and other artefacts from the final exposure, which allows you to pull through more meaningful detail of the actual night sky objects.

Depending on the subject and its brightness, long exposures - sometimes in excess of five or even ten minutes - are usually required to reveal enough detail, and with longer exposures comes increased noise levels and greater risk of visual artefacts like star trailing, light pollution and light trails from aircraft flying overhead. These all produce challenges during both the stacking and editing process that the software must be able to tackle.

There’s also the requirement of being able to calibrate the image frames before they are stacked together. This is achieved using a variety of calibration frames, which are often shot during the imaging session, although with temperature-controlled sensors and mounted telescope systems this is not always necessary.


The Stacking Process In Affinity Explained

Stack Persona (alpha) |
Stack Persona (alpha)


The stacking process is easy in Affinity Photo: the light (image) frames and calibration frames are loaded into separate file lists within the Astrophotography Stack Persona, and you can configure various stacking options such as the clipping threshold, which is useful for rejecting aircraft light trails and other inconsistent pixel information. You then click the Stack button, and once the images have stacked you will see the final tone-stretched result. If you need to modify any settings, you can do so and click the Stack button again (with significantly reduced processing time) - each time you do this, a new layer will be placed into the Stacked Images panel at the bottom right.

Once you are happy with the result, you can click Apply and each stacked image is brought through as a layer into your main document’s layer stack. Levels and Curves adjustment layers are also provided by default which perform the initial tone stretching - you can tweak this further if required.

Stack Persona (white Fill) |
Stack Persona (White Fill)


For monochrome imaging, where narrowband or broadband filters are used to capture different wavelengths of light, you would typically stack each data set separately, then copy the final pixel layers into one document and blend them together. Layers may need to be aligned, which can be achieved by selecting them all and using Arrange>Align Layers by Stars.

From this point, it’s a fascinating editing process whose complexity can vary depending on the requirements of the subject. Light pollution can be tackled with the dedicated Remove Background filter, found in the Filters>Astrophotography menu. You can single-click to set sample points within the image and easily remove gradients from the background sky detail.


Remove Background |
Remove Background

The software also has a comprehensive set of masking and selection options too, so you can easily make selections of star detail or background detail, then apply adjustments and live non-destructive filters. For example, you can use a Minimum Blur live filter to reduce the intensity of stars in the image or use an HSL adjustment to reduce background luminosity whilst boosting deep-sky object detail.

Since Affinity Photo also supports macros (recordable operations that can be played back instantly), you can speed up any techniques you find yourself using frequently, such as creating luminosity masks, applying your own tone stretching or even setting up blending of the initial monochrome data layers to produce the full-colour composition.

Another technical advantage to highlight is the ability to complete the entire workflow in 32-bit precision. With the exception of Median Blur (and therefore also Dust & Scratches), all adjustments, tools and filters are available for you to use in 32-bit. This cuts out the requirement of merging or flattening then converting to 16-bit in order to continue editing, and allows you to take advantage of processing entirely in a linear colour space from start to finish, as well as making use of the extra precision.


Orion Nebula HaOIII |
Orion Nebula HaOIII


Astrophotography, much like regular photography, can quickly become an expensive hobby or profession. Therefore, in some ways, you may argue that an extra few hundred dollars spent on dedicated astrophotography software is hardly worth quibbling over rather than investing a smaller amount into a more general image editing application. However, even if budget is not a concern, Affinity Photo offers a streamlined and straightforward workflow, especially if you are used to other layer-based image editing software. It’s ideal for newcomers to the genre, but also offers several notable advantages to seasoned astrophotographers as well, particularly for non-destructive workflows.


Even More Affinity Photo Astrophotography Tutorials

For anyone interested in exploring Affinity Photo’s astrophotography capabilities, we have a plethora of tutorial videos covering the subject available both on our website and YouTube.

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