Hello!
Whenever I have been using triplanar mapped bump maps I have always felt that there is something off, so I wanted to do a proper test.
I have set up two test scenes with two spheres and two planes, one of the planes and one of the spheres are using UV mapping, and the others are using triplanar mapping.
I used a UV test grid map to make sure the scale of the mapping is the same, and a simple image of some noise as bump.
When comparing the results, you can clearly see a huge difference in the bump map result. The UV mapped objects look as expected, but the triplanar mapped ones look very odd, rough and lacking highlights.
At first, I couldn't figure out why, but then I tried applying a Color Correction Node to the triplanar mapped image. With a gamma value of around 3.1, suddenly the result is looking more like the reference UV mapped noise.
Is this a bug, or intended result? The albedo map does not seem to be affected, as it looks the same regardless of mapping type.
Attaching renders and a ZIP with the test scenes.