I have been using the excellent Noise reduction filter by Iain Fergusson (2019) through the GIMP/GMIC-Qt Plug-in. See image. I would like to fully understand the functionalities of the various controls provided. (For example-what is an internal guide?) For this I am studying the following resources -
Are there any other resources that I could use ? Any tutorials?
It would be better if you gave us an example and told us how you are struggling with understanding the filter. The more specific your questions are, the easier it would be to assist you.
The filter uses a second image as a guide to help denoising. This image can be provided externally as two input images(layers) or can be created internally from a single input image.
Typically some processing is done on the guide image that helps the denoising of the main image. EG if you apply a curve to the guide, then you can control the strength of the denoising in different tonal areas.