Spec Maps For Rock Wall, tutorial included:

I've used spec maps before but I never really got very in-depth with them until today. The procedure I used is pretty standard in my eyes but I figured I would post how I got them to turn out the way they did. I like them, personally, the workflow went pretty easily for me. Took me about 20 minutes to turn out a good set.

First is a list of assets you need.
>Texture Map for your model
>Normal Map for your model
>Texture you want to use as a Specular Map

Note: In your model, a Lambert won't have the specular channel to place files into. Make sure you are using a blinn or phongE to use the specular channel.

First Step is to open Photoshop (whichever version you have, I personally still use CS3 because the controls are very familiar and it's very stable under large file sizes).

1) Open your normal map and your chosen specular texture. I started with my Specular Texture. This texture needed a bit more randomness to it so I duplicated it until it fit my image size and used the clone stamp tool to add the randomness I needed. I then desaturated this layer. Save as a new .png (or whichever extension you are using). Do not close the image just yet.

2) Next I brought up my Normal Map. First thing I did was to unlock the layer and add the Filter > Stylize > Find Edges. This brought out the edges based on color which matched each other according to depth from the Normals. Everything that didn't have an edge went to white. I desaturated this layer and then inverted which pops the edges out to white and everything else to black. I also went into the adjustments setting and tweaked it a bit until the edges were a little less solid. Being a rock surface I didn't want really hard edges to pop out, I wanted them a bit softer. Save as a new file and close, don't save over your original.

3) Bring your new desaturated normal map into your new desaturated Spec Texture image. I first toyed with setting the normal map to overlay but it blended in a bit too much. I chose to use the screen option and adjusted my levels to again make it a bit less solid. Optional: I still wasn't really happy with the brightness of some of the edges. I duplicated my screened normal map and set it to normal on TOP of my screen. This popped out the lines while giving softer light on the outer edges. Next, bring in your chosen texture for your model (whichever you use as a color diffuse), desature and then set it to overlay. I took mine to about 30'ish percent opacity. That finished my specular map.

Edit: In the end your layers should look like this from top to bottom:
>Overlay Texture Map
>Desaturated Normal Map
>Specular Texture Map

Again, layers may need tweaking to function in this order. They don't necessarily need to be in this order.

This gave my overall model a nice look. When the light hits the model it doesn't have a shine or an apparent dullness. Rather, areas that need to reflect a bit of light do and those that don't gave off less 'shine'.

All in all I'm happy with how my spec map came out. It will never be perfect as I'm still working on how to use spec maps properly. I'm also not trying to teach anyone but sharing how I got my spec map. I'm always open to suggestions and critiques on my work. Also, I'm currently messing with the reflection/refraction channels using my spec map and an inverted version of my spec map to bounce light and absorb light in tandem.