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.