Optimizing the UV Layout¶
When you have unwrapped, possibly using seams, your UV layout may be quite disorganized and chaotic. You may need to proceed with the following tasks: Orientation of the UV mapping, arranging the UV maps, stitching several maps together.
The next step is to work with the UV layouts that you have created through the unwrap process. If you do add faces or subdivide existing faces when a model is already unwrapped, Blender will add those new faces for you. In this fashion, you can use the UV texture image to guide additional geometry changes.
When arranging, keep in mind that the entire view is your workspace, but only the UV coordinates within the grid are mapped to the image. So, you can put pieces off to the side while you arrange them. Also, each UV unwrap is its own linked set of coordinates.
You can lay them on top of one another, and they will onion skin (the bottom one will show through the top one). To move only one though, RMB select one of the UV coordinates, and use, Ctrl-L to select connected UVs, not box select because UVs from both will be selected.
Combining UV Maps¶
Very often you will unwrap an object, such as the face example we have been using, and get it “mostly right” but with parts of the mesh that did not unwrap properly, or are horribly confusing. The picture to the right shows an initial unwrap of the face using the Unwrap from sphere option. The issues are with the ear; it is just a mush of UVs, and the neck, it is stretched and folded under. Too much work to clean up.
We can tell that the ear would unwrap nicely with just a straightforward projection from the side view, and the neck with a tubular unwrap. So, our general approach will be to unwrap different parts of the object (face, ears, and so on) using different unwrap calculations, selecting each calculation according to whatever works best for that piece. So let us begin: We select only the “face” faces, unwrap them using the Sphere calculation, and scale and rotate them somewhat to fit logically within the image area of the UV Editor.
Once we are satisfied with the face, it is time to turn our attention to the ear. First, unselect the faces you were working with. Their UVs will disappear from the UV Editor, but they are still there, just not shown. (To verify this, you can select a few faces in 3D View and it will show up in the UV Editor.)
To work on the ear, in the 3D View, we now select only the “ear” faces. You can use Vertex Groups to select the ear faces. Selecting sub-meshes is easy too, since they are not connected to the rest of the mesh. Simply selecting Linked vertices will select that entire submesh. Basically, since you are in Edit Mode, all of the selecting/deselecting features are available to you.
Now re-unwrap the ear using the Project calculation from side view, and scale and rotate them somewhat (discussed in the next section), and place them off to the side. You can do this repetitively, using different UV calculations; each re-calculation just puts those UVs for the selected faces somewhere else. Choose the calculation for each piece that gives you the best fit and most logical layout for subsequent painting of that piece.
When all of the pieces of the mesh have been unwrapped using the various calculations, you should end up with something that looks like to the Example to the right. All of the sections of the mesh have been mapped, and all those maps are laid out in the same UV texture map. Congratulations! From here, it is a simple matter of “stitching” (discussed in the next section) to construct the entire UV map as a single map.
When you have completed arranging and stitching, you will end up with a consolidated UV map, like that shown to the right, arranged such that a single image will cover, or paint, all of the mesh that needs detailed painting. All of the detailed instructions on how to do this are contained in the next section. The point of this paragraph is to show you the ultimate goal. Note that the mesh shown is Mirrored along the Z axis, so the right side of the face is virtual; it is an exact copy of the right, so only one set of UVs actually exist. (If more realism is desired, the Mirror Modifier would be applied, resulting in a physical mirror and a complete head. You could then make both side physically different by editing one side and not the other. Unwrapping would produce a full set of UVs (for each side) and painting could thus be different for each side of the face, which is more realistic).
Iteration and Refinement¶
At least for common people, we just do not “get it right the first time.” It takes building on an idea and iterating our creative process until we reach that magical milestone called “Done.” In software development, this is called the Spiral Methodology.
Applied to Computer Graphics, we cycle between modeling, texturing, animating, and then back to making some modifications to mesh, re-UV mapping, tweaking the animation, adding a bone or two, finding out we need a few more faces, so back to modeling, etc. We continue going round and round like this until we either run out of time, money, or patience, or, in some rare cases, are actually happy with our results.
Refining the Layout¶
Refinement comes into play when we finally look at our character, and realize that we need more detail in a particular spot. For example, areas around the eyes might need crow’s feet, or we need to add a logo to the vest. As you start to edit the image, you realize that there just are not enough pixels available to paint the detail that you want.
Your only choice is to expand the size (scale out) that UV face. Using the Minimize stretch or Scale tools, you expand the UV faces around the eyes or chest, allocating more pixels to those areas, but at the same time taking away pixels (detail) from something else, like the back of the head. After refining the UV map, you then edit the image so that it looks right and contains the details you want.
Another consideration is the need to conserve resources. Each image file is loaded in memory. If you can reuse the same image on different meshes, it saves memory. So, for example, you might want to have a generic face painting, and use that on different characters, but alter the UV map and shape and props (sunglasses) to differentiate.
You might want to have a “faded blue jeans” texture, and unwrap just the legs of characters to use that image. It would be good to have a generic skin image, and use that for character’s hands, feet, arms, legs, and neck. When modeling a fantasy sword, a small image for a piece of the sword blade would suffice, and you would Reset Unwrap the sword faces to reuse that image down the length of the blade.