Middlebury

Blender uv mapping

UV Mapping is the process by which the animator applies textures to an object. In order to create a texture the 3D object must be made into a 2D image. At that point the animator can paint onto the 2D representation of the surface of the 3D model. U and V are the axis of the 2D representation. In order to create a UV map the animator can use an algorithmic or manual approach. Often the manual approach is extremely time consuming. In the case of more complex objects it is often preferable to mix algorithmic and manual approaches. By default textures are attached in strips around the outside of a 3D model. Unless the texture is a plane with dimensions proportional to the texture this will result in warping. The goal of the UV mapping is to minimize this warping by telling the object how to take the texture. Hence both the algorithmic and the manual approach will attempt to cut the object in a way which will leave minimal overlaps and warps. For example a correctly UV mapped article of clothing would look similar to the sewing pattern for that article.

  • Algorithmic methods use the angles of the object along the world axis to cut the objects faces and lay them out on a 3D surface. In Blender you can specify the minimum possible angle. Then the algorithm will go through and create a seam along any edge that is larger than that angle. Usually this will be something under 45 degrees. The UV map then will be split up into groups of faces.
  • The manual method creates groups of faces by turning edges into seams. These seams are then the lines that the computer will cut along. The modeler goes selects edges classifies them as seams and then tells the computer to cut along the seam. Generally the more seams the less distortion. But as with many 3D procedures it is a balancing act. The user decide if their particular application of UV mapping can suffer from a little distortion or if perfection is required.
  • A Combined Method takes the best of both methods. First the user can manually define regions of vertices by creating seams. On a pillar the animator might define the base the top and the main cylinder as distinct regions by cutting a seam around the edges that divide them. Then the user would use the algorithm to determine appropriate cuts along circumference of the tubes. This would mean that the pillar would be broken into pieces that would be easy to model but that those pieces would be optimized to prevent distortion.

A Video Tutorial

The Digital Media Tutors have now uploaded a video tutorial for the process of skinning as described below.

An Example

  1. Open Blender delete the default cube and add a cylinder.
  2. Scale the cylinder on the z axis until it is about four times as tall as it is wide.
  3. Now in edit mode switch to edge selection. The ege selector is in the bottom header panel
  4. Now select one edge on the front of the cylinder the ring of edges around the top and bottom and one edge opposite the first edge on the back. The cylinder should look like the below image.
    how to select seams

  5. Now Press control+e for the edge specials menu. Choose mark seam. The edges will now be highlighted orange.
  6. Split the 3D view and change the right window to the UV/Image editor through the Current widow type menu. Change the mode of the object from edit mode to the UV face select mode through the mode menu.
  7. Now press a to select all of the faces on the cylinder. Then press U to unwrap. You should see two circles and two rhombuses in the right window.
  8. You want to clearly separate the UV coordinates of each face. You can do this using the same controls as in the 3D view. Hence select one of the vertices of a UV coordinate and press l to select all linked. Now scale it down. Do the same for the other four parts.
  9. Now navigate to the UVs menu in the UV/Image editor window. Go to the scripts menu at the top and select save UV face layout. Save it to the desktop keeping the defaults. (Note the size by default is 512 it is best to have smaller textures about 128 or 256 for video games and possibly larger for static models 512 is about right for animation. Texture size is a large factor for the processing requirements of 3D applications.)
  10. Open up the UV texture in an image editor like gimp or photoshop. Paint on the faces. Add or preserve a black line on the edge of each piece this acts like airbrushing. It gives the model a look of having strong geometry. Give each piece a different color so that you can see how UV editing works.
    a sample texture
  11. Save the texture that you make in the image editing program as a .jpg file in a directory that you can remember. Go to the UV/Image editor menu and select image=>open then choose your texture. Now you will see that the texture is applied to the UV coordinates specified.
  12. This is the basic procedure for a manual UV mapping. At the step where you pressed U and that unwrapped the coordinates there where other choices for unwrapping procedures.

Other Types of Unwrapping

  • unwrap- is the manual type
  • cube projection- automatically creates a cube UV
  • cylinder projection from view- automatically creates a cylinder UV based on the current perspective
  • sphere projection from view- automatically creates a sphere based on the current perspective
  • projection from view- automatically creates a UV projection from the current perspective.
    • current view- means that the front view should be less warped then the other parts of the UV.
  • All of the others besides the last are different ways of choosing a perspective to base UV mapping on.
  • Unwrap(smart projections)- is the algorithmic means described above. You can use this with seams to achieve a highly quick and satisfying result. Nothing will ever be as clean as manual but sometimes speed trumps perfection.
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