This i'm calling glare, it's just an additive solid colour being modulated by the magnitude of the gradient. I guess it's a sort of HDR bloom effect.
This is a fancy emboss using a phong shading model for lighting with a small ambient source. I'm using the opportunity to learn a bit about lighting models - the last time I did anything related to lighting was on an Amiga and that amounted to little more than a dot product of the normal for 'light sourced vectors'. I finally get to use my Foley & van Dam!
This is the same algorithm with different parameters - upped the ambient, reduced the diffuse and specular and with a slightly smaller gaussin filter. Gives more detail to the surface as well as showing the original image (which could also work in colour).
I'm using a differential of Gaussian to calculate the gradients in each direction. This is basically a tunable sobel filter.
From these gradients I just directly create a surface normal which feeds into the phong calculations.