I’m starting from a photograph of a relief, lit from above, something like https://en.wikipedia.org/wiki/File:UnfinishedStele-NefertitiPouringWineIntoAkhenatensCup.png
I want to extract the underlying image as if the relief had been printed onto paper. Whereas Emboss takes a kind of ‘differential’ of elevation, I want to ‘integrate’ it, so for example low values will be given to pixels above a shadow and below a light part of the image.
In GIMP, I’ve tried ‘Edge Detect’, but it’s adding more complexity, not simplifying. I don’t think a Convolution Matrix will help either, as I want to colour the whole elevated area, not just that near a shadow or highlight. I’m wondering if I need a GIMP Python script or any other software will help.
Sorry, this question may be more to do with image processing than graphic design, but it is to be used for a graphic. It may be possible to trace and recreate the image, but I wondered if it could be done in software.
In fact there are a range of tools for extracting and extrapolating “texture maps” for 3D modeling textures based in a single input photo, and they can create heightmaps, reliefmaps, base colour maps etc etc. I think this might get you the results you want.
I would first run a perspective correction, and then apply such a tool.
The one I use most (Allegorithmic’s B2M) isn’t freeware, but there are freeware tools out there, including Materialize, AwesomeBump, and NormalMap Online which are pretty decent equivalents, including, if my memory serves, somewhere there’s a GIMP plugin or two for this task type.
I’ve some results from doing a very rough and quick session of what I’d mentioned above as a proposed workflow – I spent about two minutes in Affinity Photo, first with the perspective correction and then with the clone brush and inpainting tools, then pushed the resulting image into Allegorithmic’s Bitmap to Material application, where I set no special parameters and output only a few of the available dozen or so output types; very little manual time in this session at all.
I don’t know if any of these images will answer your need individually, but I think perhaps by combining a couple, you will have almost exactly what you need (I’ll leave that call up to you) but I think the curvature map could be combined with the base colour and then use the height map as the main driver / mask and you’d be there.
Hope this helps some.
P.S. – I looked again, and in Affinity Designer I overlaid the base colour map and the height map (height map on top with multiply opacity mode) and was able to do a quick manual trace – it’s only rough, but just in case it helps…