The image data files are not actually loaded into memory when a File->Load task is performed. Only the file header and EXIF data (if applicable) is read and the file information is stored in memory and displayed in the file list on the left side. When a later pre-processing or processing step is done, the image file is read from disk into memory, the processing performed, then the results is written back to disk. The information for the new file(s) created are updated to the list.

As an example such as Dark Stacking, only one file at a time is read from the disk and added to the stack, then discarded, before reading the next file and adding to the stack. There will be some tasks such as median stacking which require all files to be in memory before processing can start, but where applicable, files are only resident in memory when needed.  The reasoning behind this, is that the software is less likely to have memory overload problems if a very large number of files were being simultaneously processed.

The saved file output format can be selected under Edit->Parameters menu. Currently, PNG format is shown as the default Save format, which maybe not what you want.

  • Saving as TIF files are supported, but it is uncertain if OpenCV is using full 16 bit option for TIF files.
  • For JPG format, 100 is optimal quality and maximum file size. It will still be slightly lossy, but will be as good as can get with JPG.
  • PNG format is reported to be lossless and the parameter is the amount of computation effort that is applied to compress the file. 9 is maximum effort for a smaller file size. 3 is apparent a good compromise. 0 is no compression and quickest.

If you use PNG with quality = 9, the file save process may be quite long at the completion of each processing step. The quality of the image wont be any different from other quality options, but it will have a smaller file size. A value of 3 seems a good compromise.


Loading Dark, Bias and Flat files

By default, the loading and processing options for dark, bias and flat files are not visible.  To allow these options, go to the Preferences menu (Main Menu -> Edit - >Preferences) and set the processing level to Level-2.


Viewing images

There are two ways to view an image.

  • The first way is to single-click on a file name when the “Preview and Exif” tab is at the front
  • The second way is to right-click on a file-name and a separate ImageViewer will pop up.

There is a third type of image window that may automatically come up at times for some processing options, and this is from OpenCV. This window is controlled by the processing.