I have a high-res scanned image that I want to edit and then reprint. The scans have a certain level of noise that I'd like to mimic in my edits so that the editing is not obvious. I'm using GIMP.
As an example, I'd like to paint over the white and yellow component on the left with a blue that matches the color and noise of the blue on the right:
Ideally I could do this with some kind of painting or brush tool (i.e. click and drag) so that these kinds of changes, of which I have to make many, could be done quickly. However, I couldn't find a setting or dynamic for the pencil or paintbrush or airbrush that reproduced this noise.
Another strategy I've tried is to apply a sample average blue uniformly within a selection of the part I want to paint over, and then try to apply the noise as a second step. And possibly mend the boundaries afterward as well. This is as close as I've gotten with an RGB noise followed by a gaussian blur (edited selection is on left side):
This strategy is less appealing since I have to work with selections and two filters rather than a more flexible, quicker brush-style approach. Is there a way I can use a brush approach for this? Or another, better way than what I'm doing here?