About astrophotography stacking

Affinity Photo's Astrophotography Stack Persona is used to create high-quality celestial images.

It requires light frames, which are long exposures of the night sky, and several kinds of calibration frame. Stacking of the light frames increases the SNR (signal-to-noise ratio).

The stacking process is performed to 32-bit linear unbounded floating point precision throughout, which maximizes your options for tone-stretching and other post-processing you might perform.

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 flat

End result

An example end result from the Astrophotography Stack Persona with additional post-processing applied

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

File formats

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

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.