I am trying to create a bumpmap of a spiky texture. I want low, pointy spikes that gradually slope up from the surface, similar to thorns. I have tried every kind of radial gradient to achieve this effect, but none of the bumpmaps I have created look right. I tried procedurals, but that didn't work either. Any ideas? Anyone?

try anything grows.. that will make something aong those lines

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Hexagon, Carrara, Sculptris, and recently Sketchup. 

If you want to create a bumpmap this will give you the "gradient" but I don't know how well it will "bump" (I assume you know C fairly well and PhotoShop.) 1. Create a model of your thorn. I used the spline modeler and oriented it spike up in the assembly room. 2. Insert an isometric camera and using the directors camera place it above the thorn. Switch to iso camera and using the zoom in the properties tray size the thorn in the frame. 3. Do a render in the render room selecting Photoshop format output (.psd) and check "distance" in the G-Buffers. 4. Save and then open the render in photoshop. The height map of the thorn will be in the 4th channel of the render. You will be able to copy it and make your bump map from there. If you have Anything grooves you can recreate the thorn but I don't know why you would want to. :-) The image gives a rough idea of what's going on.

wow that sounds easy too :)

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Hexagon, Carrara, Sculptris, and recently Sketchup. 

Did you try the Spike modifier?

Thanks everyone for the suggestions. I tried the Spike modifier and it wasn't really what I was looking for. I don't have Anything Grows, so I will try the Photoshop suggestion. I am trying to model a kiwano (horned melon). This is a fruit with a spiky outer rind. Should look cool if I can get the spikes right.

I think smoothing extruded polygons would work well.

www.youtube.com/user/ShawnDriscollCG

You might consider modelling the spikes. Bump maps are useful but they are never a substitute for actual geometry. With a bump the edges of your melo will remain smooth. Modelling needn't be difficult. In this example I used a fairly high resolution vertex sphere and pulled out the spikes using the magnet tool set to a small radius (0.5). I then used the cellular bump to create the texture of the skin.

Looks like a horned melon to me! Nice work!

Question for Sailor Ed... I modelled a spike shape and rendered it as a Photoshop file. Where are the "G-buffers" that I have to check "distance" in?

They are in the render room properties panel under the "Options" tab. They're down at the bottom, you might have to scroll.

Another option is to model a spike, remove all lights, set an isometric camera pointing directly down at it, set an elevation shader in the glow channel or use a gradient shader in the glow channel. The elevation shader requires more work to do the job, but if tweaked correctly it's a better choice. Another easy choice is to use the color gradient shader, as you can set the control points...

Very good! I can see how that would give you better control over the final result.