UV island rotation also rotates normal maps?

I’ve got a normal map misbehaving, and it seems to be because I’ve got two different UV islands, each of which belongs to contiguous parts of the mesh, but which are rotated 90 degrees to each other. I’ve verified that if I make the rotation of the islands the same, I get the same normal map for both islands. (Note: one island is the front half of a cylinder, the other is the back half. I’ve divided them up this way so I can easily center decals when I’m texture painting).

Is it not safe to rotate islands like this? Most of the tutorials/books I’ve looked at show lots of rotations of islands.

(note: I tried to attach the blender file, but I got errors).

[edit: Marking this as “solved” since I cleared out all the normal maps in the project, deleted the nodes, and started from scratch. Everything seems fine now, but I don’t understand the problem.]

Its just way normals map work.
R- Up
G - Left
B- Intensivity
(i think so)

Try to place rotated UV in ntrotated place and look at preview.

Normal maps encode the x, y, and z coordinate differences between two surfaces as R, G, and B values. I’m not sure if that’s the actual order they correspond but that’s the idea anyway.

Are you saying that it should be fine to have the two islands with such dramatic color differences? That makes sense to me, but I’m getting bad results when rendering in cycles. There’s a seam and a sudden shift in light level where the two islands meet.

[edit: I turned the strength up to 10 to make the problem more obvious, but you can see it even with a strength of 1]

.blend file: http://www.pasteall.org/blend/30811


(I regenerated normal in internal cause you didnt pack it)

Huh. I “reset” some of the materials on the high & low poly meshes, rebaked the normals and it renders fine now. The normal map image hasn’t changed, but the render looks good. Don’t know exactly what I did to solve it, but I’m marking the topic as solved anyway.