Workflow options

The possible workflow scenarios are shown below. Processing with dark, bias and flat files falls into the optional category

The simplest option is to simply load a number of images and stack them all together. The more complex workflows include alignment and image processing.

If Manual Alignment irs required, the alignment points are selected in Pre-Processing, then are applied during Processing.

Auto-Alignment is good for small alignment shifts or fine tuning. If large shift are required, then Manual Alignnment should be done first, followed by Auto-Alignment.

The main "Processing" module includes the following

  • Dark Subtraction
  • Bias Subtraction
  • Flat Correction
  • Automatic Dispersion Reduction
  • Apply Manual Alignment Shits
  • Negative Image

Any of the processing options shown above can be selected. The minimum number of processes expected is one process and the maximum is all available options for processing. The options are not dependent on each other, but they will be performed in the order from top to bottom as shown on the Processing page. All of the selected processing options are done with-in one read/save cycle, to avoid image degradation that may occur if using multiple saving operations and a lossy image (JPEG) saving method is selected.

Two levels of available processing options are defined:

  • Level-1 excludes some extra options, which may not be required for some users (default).
  • Level-2 includes the Dark, Bias and Flat processing options. These are grouped as optional in the workflow chart below..

Starstack workflow

 

By default, the loading and processing options for dark, bias and flat files are not visible in the data loading and processing menus (default is Level-1 processing).

To allow these extra processing options (Level-2), go to the Preferences menu (Main Menu -> Edit - >Preferences) and set the processing level to Level-2.

 


Pre-processing

Pre-processing steps are steps that dont have any immediate effect on any images. The pre-processing steps either assist in determining processing parameters, or compute auxillary files such as dark, bias and flats for later application to the image files.

  • Dark/Bias/Flat stacks. Computes a mean stack of the checked files that are loaded as either dark, flat or bias
  • Flat modelling. Simulates a flat file based on a single parameter called “flat coefficient”. A larger value has a greater falloff towards the edge of the image. An image is required to be present in the image list before this option can be run, since information on the image size is needed and is got from any file in the flat list. 
  • ADR. This is an attempt to reduce the severity of atmospheric dispersion that occurs on images shot at lower altitude angles close to the horizon. It simply shifts the red pixels down by a certain pixel count, and shifts the blue pixels up. The photo angle relative to the horizon is required, and is the parameter called camera angle. Note that if doing eye-piece projection photography, an additional 180 degrees needs to be added (or subtracted).
  • Manual Alignment shifts. Allow to identify a single, or a pair of points on each image for later alignment.
    • Single point alignment means that the images will be aligned at the selected point by X and Y translations.
    • Two point alignment means that the images will be first aligned mid-way between the 2 selected points by X and Y translation, and then a “best fit” rotation is applied so the two selected points will overlay. If the points were not accurately picked, or the images suffer from lens distortions, then the final overlay may not be exact.

Manual alignment can be useful step to perform before later automatic alignment, if the input files are not very aligned to start with. (Poorly aligned files may fail automatic alignment, and will also take longer to process)

 


Stacking Dark, Bias and Flat files

Right clicking on the File Type for Dark Files, Bias Files and Flat file brings up a menu that also includes options for stacking these files. (Previously, these stacking options were in the pre-processing Menu)

Starstack

For regular Image Files, stacking is done within the Processing or Stacking page.