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I'm currently modeling my game character in Blender (see below picture).

What is the difference between a subdivision surface modifier and a multiresolution modifier? I know they smooth the surface but are there specific characteristics to using each and what are those?

low poly character model

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When using the sculpt tool, you will sometimes want to add more detail than your mesh has vertices to support. You could add vertices by subdividing the mesh, but subdividing the mesh will increase the complexity of the model, slowing blender down, making the model larger, making the mesh less usable for certain applications (like games).

Sub surface allows you to increase the vertices as a modify, but isn't affected by sculpting. It's purpose is to add geometry to the whole mesh and make a lower poly figure a higher quality without increasing the complexity of the mesh. You cannot move, alter or sculpt the new vertices without applying the subsurface. It wasn't designed for it.

Multi resolution modifier was added to allow you to add geometry for the purposes of adding detail to a sculpt. Vertices in a multi res modifier are affected by a sculpt even when not applied. This allows you to sculpt with more verts than the base mesh has. This is useful because you sculpt at a higher resolution, bake out the sculpt as a map, and apply it to the mesh as a normal map, without increasing the actual number of vertices the mesh has.

So, if you're not sculpting, sub surface and multi resolution are logically equivalent, and the preference is for sub surface (less data in memory, easier interface). If you are sculpting, and want to keep the mesh low poly, but need more detail in the sculpt, use multi resolution and then bake out the normal map (which can then be applied to the surface of the object as a texture in the cycles node editor).

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  • $\begingroup$ I appreciate the clarity in your response. Very easy to follow, thank you. $\endgroup$ – John H Apr 26 '14 at 1:29
  • $\begingroup$ This was a really helpful solution for me! It should be accepted as a solution. $\endgroup$ – babaliaris Jun 11 at 23:59
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From the wiki:

Another way to subdivide is with the MultiResolution Modifier. This differs from Subsurf in that MultiRes allows you to edit the mesh at several subdivision levels without losing information at the other levels. It is slightly more complicated to use, but more powerful.

In other words:
Changes made to the mesh (via sculpting) will be applied to lower and higher subdivision levels as well as the current level. To apply changes to the base mesh you must press Apply Base on the modifier.

This is different from the subserf modifier, where the subdivided mesh cannot be edited unless the modifier is applied.

Baking:

Another advantage of the multires modifier (in certain cases, of course) is the normal map baking workflow:

  1. Model low poly mesh (in this case a cube) and UV unwrap (you can UV unwrap later too)

    enter image description here

  2. Add multires and subdivide

    enter image description here

  3. Sculpt high res details

    enter image description here

  4. Bake normals from multires (bakes the normals from the highest subdivision level to the current preview subdivision level mesh:

    enter image description here

    Note that you can also bake normals to the base mesh if the preview level is 0.

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  • $\begingroup$ This is a great step-by-step. Thank you! I am following along and I got this message after I applied seams and unwrapped !Error. I need to read up on how to unwrap and apply a texture, then bake. $\endgroup$ – John H Apr 26 '14 at 1:30
  • $\begingroup$ @JohnH You must have an image open in the UV image editor when unwrapping (you can select/create the image before or after unwrapping, but it won't be "applied" unless it's displayed under the UV layout while in edit mode). To create and "apply" a new image to an existing UV map, click New in the header of the image editor while in edit mode (with the unwrapped object selected, of course). $\endgroup$ – gandalf3 Apr 26 '14 at 6:08
  • $\begingroup$ Thank you for clarifying the steps. Okay, I've baked the normals from the multires. Now I have to read up on how to apply that normal map to the texture and back to the low-poly model. It's fun learning how all this comes together! $\endgroup$ – John H Apr 27 '14 at 8:17

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