It’s not infrequently that I stumble upon forum posts on hobbiest game dev sites where someone proclaims in response to a question, “no – you can’t make normal / bump maps from textures”. The logic being that there is absolutely nothing in a texture map that would in any way yield useful depth information. This is certainly true – and it would be also be true to say, “you can’t make really really good normal maps from just a diffuse texture”.
But you can make normal maps which serve a purpose – you’ve got a texture which had no bump map packaged with it, you’re not an artist, and anything half decent is better than nothing. It’s also staggeringly easy and requires no skill, yet I almost never see it mentioned on the internet in these discussions.
So I present to you, Photoshop’s “High-Pass” filter:
Take your texture, and do:
Filters -> Other -> High Pass
Play with the slider until you get something bump-mappy (usually quite low values), desaturate the image, done. You’re welcome 🙂