control subdivision using an image?

I’m very much a noob so please forgive me if this is a stupid question.

I’m want to apply a very high resolution displacement map to a UV Sphere. I could just subdivide to get the millions of faces needed but this seems a waste as I only need the extra faces in a relatively small proportion of the sphere. I could subdivide by hand, but I was wondering if there was a way to use an image to control the areas affected by a subdivision modifier? E.g. have white areas subdivide and leave black areas alone?

Thanks for any help!

Put a subsurf modifier first (above) and have it at a higher level (?3-5) and put a displace modifer after (below) in the stack. Use the image texture for the displace.

could have a look at EWOC tools is one in there called deathguppie that subD’s only selected areas
but you have to select them yourself

Thanks for your replies!

blenderallday : but won’t this subdivide the entire UVSphere, and not the areas I’m interested in? I may do it this way, although with all the extra faces rendering will take much longer

heddheld: thanks, I’ll take a look at the tool. I’ve done a few experiments with just manually selecting faces to subdivide and it works OK, although I will probably leave it until I’ve fixed all the other problems with the scene!

I see. Well since it’s just for mountains, and not something like text (which is obvious when it doesn’t have perfectly sharp edges), you probably don’t need much subdivision, I would think 3 or 4 would be plenty. You could also bake a normal map from a multires version on a low poly mountain sphere. I suppose it depends how tight a shot and how close to the mountains you get.

Sometime when I need fine detail, I delete all but the verts I need, sculpt at a level 5 or 6 on the small area, bake the normals, and stitch the map together in photoshop.

In your case you would delete all but the “american” verts. dupe it. subdivide it a bunch. Add a displace and apply it. Bake the normals. Use the map on the low poly version.

You could “paint” the extra detail in sculpt mode using Dynamic Topology. Wouldn’t be automatic, but you can just manually trace over your texture to keep the details mostly just where needed.