Starguide - A Practical Guide to Astro-Photography

When the whole image cannot be used to sample the background, a usual way to restrict sampling to background pixels is defining a preview and selecting it as the background reference image. In these cases a much better solution is using a region of interest (ROI). In ColorCalibration, the background reference ROI defines a rectangular area of the background reference image that will be sampled to compute mean background values. The ROI is specified by four values expressed in pixels: the coordinates of its top left corner and its width and height. Instead of entering these values directly you can acquire them from an existing preview by clicking the From Preview button.

To enable the background reference ROI section, you have to check the corresponding Region of Interest group title checkbox. ColorCalibration also provides a white reference ROI to define its white reference, and the BackgroundNeutralization tool also has a similar ROI functionality. When using ROIs, you usually will leave the white reference and background reference images with their default blank values (indicated as <target image> on the ColorCalibration interface). This has the advantage that the process instance so defined is reusable: it can be applied to any image without requiring existence of specific previews. This is especially important to integrate ColorCalibration instances with ProcessContainer.

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