Definitions and workflow
Astrophotography is the process of capturing images of celestial objects. It involves several steps, including preprocessing and processing, which are distinct but related.
Preprocessing is the initial step of working with raw astrophotographic data. It involves preparing these data for further processing. This step typically involves dark current subtraction, flat field correction, and correction of other basic problems such as removing hot and cold pixels.
Processing refers to the post-processing of the preprocessed data, generally after stacking. This is where the astrophotographer applies various techniques to enhance the final image and bring out details and features. These may include sharpening (deconvolution), color calibration, noise reduction, and stretching the image to increase the visibility of faint details.
In short, preprocessing sets the stage for processing by ensuring that the data is in an appropriate form and cleaned of unwanted signal, while processing is about bringing out the best in the signal to create the final image. Both steps are important in the astrophotography process, and the quality of the result depends on the skills and techniques applied at both stages.
In Siril, the main preprocessing is done following the order of the tabs in the right pane and requires the use of master files. This is a process that can be automated quite easily and the scripts provided in Siril perform this task. The image processing is processed via the dedicated menu Image Processing. This process is more difficult to automate because it is specific to each image and consists of an iterative work.