When you’re UV unwrapping in Blender, it can sometimes happen that a texture doesn’t show the way you had intended it to. Instead it may appear rotated or mirrored (flipped).
Take the above example of a simple frame with a picture in the middle. When I originally added the texture file after unwrapping, the crab was displayed upside down, like so:
What had happened? The UV map looked OK, did I make a mistake? Did Blender make a mistake? Nah, neither was true. I used the Pack Islands feature though, and in that case Blender may rotate islands randomly to maximise the space of the UV Map. Blender only did what I asked him to do.
Fixing rotated textures
It’s very easy to fix rotations: select the faces in question (either in the 3D view or the UV view), then hover somewhere inside the UV view and use the standard rotation command: R X 180 (followed by return). This will rotate the selected faces by 180 degrees, turning them upside down.
Fixing mirrored textures
Blender may also flip or mirror textures when packing islands, in which case my picture could appear like this:
We can fit this phenomenon with the scaling command: S X -1 (followed by return). This will scale our selected faces along the X axis and inverse-stretch them, thereby flipping the image.
Notice that the UV map as such does not change visually, nor should it: we want our texture to remain in the same place. Also, when issuing those commands, make sure you position your mouse inside the UV view, NOT the 3D view – otherwise you’ll change the actual geometry instead of the UV coordinates.
When UV islands are packed too tightly together, there’s little to no room between them. That’s great because it makes use of every available pixel on the UV Map, however when it comes to texturing in Photoshop, selecting separate islands is very difficult.
Blender has a nice feature that lets us add a margin in between UV islands. It’s a little tricky to find. Here’s where to start looking for that menu.
Unwrap your object. Use the UV Editing layout for this, or have a 3D View and a UV Editor showing side by side. Select all islands in the UV window, then hit CTRL + P to pack those islands. The menu is also available from the menu: UVs – Pack Islands.
By default the margin between islands is very small. To change it, bring up the Tools Palette in the 3D View by pressing T. It’s the pane that comes up on the left hand side of the window. At the very bottom of it you’ll see the Pack Islands window, and a margin property you can set. Try 0.02 for a slightly larger margin (I believe the default is 0.001).
If you don’t see this window, watch out for a little plus icon at the bottom of the Tools Palette – it maybe collapsed (it does that sometimes).
Unwrapping UVs is tough – no matter in which application (apart from ZBrush perhaps, where everything else is really difficult). Here’s how to get started with UV Unwrapping in Blender.
Load an object and make sure you’re in Edit Mode. This is only allowed with a single object selected. Disable any subsurface or smoothing that’s applied on the object so that we have less vertices to work with.
Next switch to the UV Editing workspace (UV View on the left, 3D view on the right). It looks something like this:
On the right hand side, make sure the Shading/UV tab is showing – it contains some vital tools for this endeavour. Choose edge selection and start marking seams for your unwrap. It’s easy to ALT-RIGHT-CLICK to select edge loops, or use the Select Menu for more funky options. Continue reading Getting started with UV-Unwrapping in Blender→