You may have heard the term ‘stacking’ in relation to image editing before, perhaps most commonly in reference to astrophotography, where several long exposures are merged together to reduce noise and composite star trails for a more exciting result.

Affinity Photo for desktop tutorials Watch tutorial and quick tip videos for the fastest, smoothest and most precise creative software. Magnifying glass icon to highlight a search field. All Videos Basics Advanced Corrective & Retouching Creative Tools Filters & Adjustments. Blend images together and achieve powerful composite results easily with stacking. Affinity Photo for desktop tutorials Watch tutorial and quick tip videos for the fastest, smoothest and most precise creative software. Magnifying glass icon to highlight a search field. Increase the signal to noise ratio of your imagery by stacking a burst of images. Affinity Photo for desktop tutorials Watch tutorial and quick tip videos for the fastest, smoothest and most precise creative software. Magnifying glass icon to highlight a search field. Here we see how EASY it is to create a close up image with Focus Stacking in Affinity Photo. On the Layerspanel, click the Stack operator icon on the Live Stack Group. The default operator is Median as indicated by the icon. From the pop-up menu, select a stack operator suited to the type of photos you are stacking (see above). The icon will change depending on the operator selected.

There are many uses for stacking besides photographing the skies, so let’s jump in and demystify this term.

What does stacking do?

Stacking takes a series of images (sometimes aligned beforehand) and averages their contents, looking for changes between the images. How it performs the averaging is determined by a mathematical operator—most commonly, this would be Mean or Median (remember those from Maths at school!?).

That’s how it works technically—its practical use still remains as clear as mud, so let’s put stacking into practice:

Exposure Stacking Affinity Photo

Object removal

Sometimes when shooting a scene, there are people in your composition and there’s nothing you can do about it. You could come back another time, of course, but that may be impractical and the lighting may have changed. However, taking several shots of the same composition allows you to remove everything that changes between shots; in most cases, the people.

Stacking In Affinity Photo

This technique does rely on your obstructions moving between shots. If you have static subjects, like people sitting or loitering, they likely won’t move enough between each shot to remove them effectively. This method of stacking is best applied to busy scenes where there is a constant hustle and bustle of pedestrians and traffic.

Object removal stacking is a very similar principal to aligning your images and selectively masking areas to remove unwanted elements. Performing a Median operation on the images will achieve a similar result whilst cutting out the manual work involved.

Noise reduction

Digital sensor noise is sometimes unavoidable and mostly undesirable. Low light photography, unless shot with a tripod, requires high ISO values and large apertures to achieve suitable exposures, and that means noisier images.

Noise performance benefits as sensor technology improves over the years. Despite that, noise can prove tricky to remove. Noise removal algorithms do a very respectable job at cleaning it up, but there is still a loss of detail, noticeable in the ‘waxy’, smooth appearance of subjects that should have fine detail.

Sensor noise is random—it’s never the same in each frame. Instead of taking one shot, we can take a burst of shots and stack them. When we average those shots, we are identifying and averaging anything that changes from shot to shot, which includes the noise. By doing this, we are increasing the signal-to-noise ratio, and can therefore more accurately reconstruct fine detail in the image.

Exposure merging

Exposure merging is not HDR, nor is it a substitute. However, by stacking together different exposures of the same composition, averaging them can give the appearance of more dynamic range in the image. This provides a great starting point to do some further work on the image with more tonal range to play with.

Long exposure simulation

An unexpected but surprisingly effective use of stacking is to simulate long exposure photography. Producing good long exposure photography requires certain equipment; notably, a form of stabilisation (such as a tripod) and neutral density filters to reduce the amount of light entering the lens, thus allowing slower shutter speeds.

In the event of factors such as forgetting to bring these pieces of equipment, not being able to budget for them, or simply not wanting to carry them around, we can take several shots of our intended long exposure subject (typically water) and average between them. The effect, while not as striking, is not too dissimilar to that of a genuine long exposure.

Exposure blending

Maximum and Minimum operators average the greatest and smallest RGB values respectively, and they work best on images that either have a dark background and bright subject (Maximum), or a light background and dark subject (Minimum). In the above example, several shots of a bonfire shot against a dark background are averaged using the Maximum operator, which results in the brightest areas of each image being combined to produce a more powerful-looking image.

Stacking in Affinity Photo

Affinity Photo offers an intuitive stacking feature (via File>New Stack) that automatically aligns a series of images and creates a stacked group with them. Changing the stacking operator for different results is a simple case of changing the method from a dropdown on the Layers Panel.

We have a selection of video tutorials that cover stacking:

About calibration frames

Calibration frames help to clean up imagery, by identifying and removing noise from the light frames—the excess of it, at least—as well as dust spots, vignetting and other artefacts.

The use of calibration frames is optional but strongly recommended.

Noise is inherent in the shooting environment and is influenced by several factors, including: overall thermal conditions, which can vary over time; background electrical interference in the camera; and hot pixels in the camera sensor. For example, hot pixels could be misidentified as stars, affecting alignment during stacking.

Types of calibration frame

Affinity Photo can process four kinds of calibration frame, each of which identifies different noise.

• Dark frames—identify hot pixels and thermal noise, arising from long exposure times, to be cleaned from the light frames. Taken during the same session and at the same shutter speed as light frames but with the lens cap on.
• Bias frames—identify electrical read noise from the camera. Taken at the fastest shutter speed available with the lens cap on.
• Flat frames—identify artefacts such as dust specks and lens vignetting, ensuring evenly illuminated images. Captured during the same session as light frames.
• Dark flat frames—to pre-process the flat frames by cleaning noise from them, like dark frames do for light frames. Taken at the same shutter speed as the flat frames.

Bias

Flat

End result

In practice, multiple frames of each type are used to improve the SNR ratio and improve the end result.

File formats

Focus Stacking In Affinity Photo

Light frames and calibration frames should be RAW or FITS (Flexible Image Transport System) files from a DSLR or astronomy camera, respectively.

Focus Stacking Affinity Photo

They must be unprocessed for best results to avoid assumptions being made about white balance and tonality, which are approximated later in the compositing process.

Affinity Photo Astrophotography Tutorial

FITS (Flexible Image Transport System) is a file format commonly used in astrophotography that can contain extra metadata not found in RAW files. It is usually captured by CCD and CMOS astronomy cameras used with telescopes.