How to perturbate surface normal from height map

Question

I'm working on a bumpmapping implementation in my own 3D tracer. And to be really short - I want this result:

I've been reading pages and pages about bumpmapping, heightmaps, normal maps, ... and I think I understand most of the subject, the difference between all above etc etc. (I got perlin-bumpmapping to work - result ) The only thing I don't get is how to actually perturbate the surface normal from an object given a texture image. Most papers and pages are more than slightly vague on that subject.

First I figured you'd just add an image-texture to your object, for a given pixel you'd calculate the rgb color from the texture and then calculated a lightness factor from the rgb value (something like a grayscale value,...) and perturbated the normal with it before adding light effects. - I want(ed) to calculate the normal on the fly.

Question: if the above is even possible: how to perturbate the normal given the lightness-factor? And if I'm wrong here, any tips/links that could help me work my way up to given result would be greatly appreciated.

Question 2: If the above is not possible with any given rgb image, could anyone explain how to perturbate an image given a heightmap? like the first image on wikipedia Thanks a lot.

P.S: I'm doing/have to do the implementation in Java.

Answer 1

This is a tutorial in Cg ( a shader language) for bump mapping by nVidia . I've used this idea a few times. When bump mapping, the normals are NOT perturbed. They are sampled from the normal map you supply. The trick is in how to apply the sampled normal with the object space light and half angle vector, when doing lighting calculations. I believe the tutorial explains this in some detail.

In a height map you actually have the distance of the object from the camera/light saved in a texture and you use it for calculating occlusion etc in addition to perturbing normals. This GPU Gems chapter explains how to combine a height map with a normal map, getting both the surface details AND things like ambient occlusion in the same go.