Region of Interest Processing

Siril offers Region of Interest (ROI) processing for some functions. ROI processing serves two purposes:

  • For image operations that are slow to compute, such as deconvolution, it allows processing only a small portion of the image while experimenting to find the ideal parameters. This means the operation completes much quicker on the small ROI and allows the desired parameters to be chosen much more quickly.

  • For image operations that affect the look of the image such as stretches, saturation tools etc., it can be convenient to use ROI processing to compare side-by-side an unprocessed and a processed area.

ROI processing is not universal to all image operations in Siril. In fact, there are a great many where it wouldn't make sense, for example geometry operations where the contents of the ROI would be mapped to a different part of the image. ROI processing is not supported for image operations that take multiple input images, i.e. Star Recomposition, RGB Composition or Pixel Math.

Operations supporting ROI Processing

The following image operations support ROI processing:

  • Deconvolution Deconvolution can be very slow, so ROI processing allows for quicker trialling of options on a small part of the image in order to find the best settings for your image.

  • Noise Reduction Noise reduction can also be slow to process, so ROI processing allows for quicker trialling of options.

  • Asinh Stretch A user may wish to examine the effect of asinh stretch, or any of the following image operations, side by side with an unprocessed area. ROI processing allows this.

  • Generalized Hyperbolic Stretch

  • Histogram Stretch

  • Color Saturation

  • Median Filter

  • Remove Green Noise (SCNR)

No other image operations support ROI processing.

Note

ROI processing is not generally intended as a means of processing only part of an image.

In image operations with an automatically updating preview, the preview will appply to the ROI but when Apply is clicked, the entire image will be updated.

In image operations that do not have an automatically updating preview, when a ROI is set a Preview in ROI button will become available. This serves as a manual preview button, so you can preview a range of settings in the ROI until you are happy. Once the settings are as desired, clicking Apply will apply the operation to the whole image.

Setting the ROI

There are two options for setting the ROI:

  • Manual This option requires the ROI to be set and cleared manually using the right mouse button menu, in the ROI ‣ Set ROI to selection sub-menu.

  • Automatic from selection This option automatically synchronizes the ROI with the current selection, and automatically clears it when the selection is cleared.

These options are mutually exclusive and the preferred option can be configured in the User Interface tab of the Preferences dialog.

Clearing the ROI

In manual ROI setting mode, the option to clear the ROI is located in the right mouse button menu, in the ROI ‣ Clear ROI sub-menu.

In automatic ROI setting mode, simply clear the current selection and the ROI will clear.

The ROI will also automatically clear on the following occasions:

  • When the current image is closed,

  • When a new image is opened,

  • When a sequence is open and the visible frame is changed.

Visualisation

When a ROI is set, it is shown in the image window as a red dashed box in the same style as the selection box. However, when an image operation dialog is opened and the image operation supports ROI processing (or if a ROI is set when such a dialog is already open), the ROI outline will change color to green, indicating that ROI processing is enabled for the current operation.

Siril Commands

Siril commands ignore the ROI, even if run in GUI mode from the command line, and even if the same image operation does support ROI processing when called from the GUI. The ROI is intended as a quick preview, whereas commands are intended to operate on the whole image. If a ROI is in place when a command runs it will be ignored, but not cleared, so it will still be available for subsequent operations that do support ROI processing.

Color Space Transforms

Any operation to remove, assign or convert the image's ICC profile will clear the ROI, if one is set.