From BlenderWiki
Mesh smoothing
As seen in the previous sections, polygons (i.e. meshes) are central to Blender. Most objects are represented by polygons and truly curved objects are often approximated by polygon meshes. When rendering images, you may notice that these polygons appear as a series of small, flat faces. See (Simple un-smoothed test object).
Sometimes this is a desirable effect (like with cut gemstones), but usually we want our objects to look nice and smooth. This section shows you how to visually smooth an object, and how to apply the Auto Smooth filter to quickly and easily combine smooth and faceted polygons in the same object.
The last section shortly talk about the possibilities to smooth a mesh’s geometry, not only its appearance.
Smoothing the entire mesh
The easiest way is to set an entire object as smooth or faceted by selecting a mesh object, in Object mode, switching to the Editing context (F9), and clicking the Set Smooth button in the Link and Materials panel shown in (Link and Materials panel).
The button does not stay pressed, it forces the assignment of the “smoothing” attribute to each face in the mesh, also when you add or delete geometry.
Now, rendering the image with F12 should produce the image shown in (Completely smoothed).
Notice that the outline of the object is still strongly faceted. Activating the smoothing features doesn’t actually modify the object’s geometry, it just changes the way the shading is calculated across the surfaces, giving the illusion of a smooth surface. Click the Set Solid button in the same panel to revert the shading back to that shown in (Simple un-smoothed test object) above.
Manually smoothing parts of a mesh
Alternatively, you can choose which faces to smooth by entering Edit mode for the object with ⇆ Tab, then selecting the faces and clicking the Set Smooth button (Object in Edit mode with some faces selected). The selected faces are outlined in yellow.
When the mesh is in Edit mode, only the selected faces will receive the “smoothing” attribute. You can set solid faces (removing the “smoothing” attribute) in the same way by selecting faces and clicking the Set Solid button.
Auto Smooth
It can be difficult to create certain combinations of smooth and solid faces using the above techniques alone. Though there are workarounds (such as splitting off sets of faces by selecting them and pressing Y), there is an easier way to combine smooth and solid faces, by using Auto Smooth.
Press the Auto Smooth button in the Mesh panel of the Editing context, see (Auto Smooth button group in the Editing context, Buttons window), to indicate which faces should be smoothed on the basis of the angle between faces. Angles on the model that are smaller than the angle specified in the Degr NumButton will be smoothed during rendering. Higher values will produce smoother faces, while the lowest setting will look identical to a mesh that has been set completely solid.
Note that a mesh, or any faces that have been set as Solid, will not change their shading when Auto Smooth is activated: this allows you extra control over which faces will be smoothed and which ones won’t by overriding the decisions made by the Auto Smooth algorithm.
Look at (Same test object with Auto Smooth enabled): only faces that have been set as smooth have been affected by the Auto Smooth feature.
Smoothing the mesh geometry
The above techniques do not alter the mesh itself, only the way it is displayed and rendered. Instead of just making the mesh look like a smooth surface, you can also physically smooth the geometry of the mesh with these tools:
You can apply one of the following in Edit mode:
Alternatively, you can smooth the mesh non-destructively with one of the following modifiers:
- Smooth – Works like the Smooth tool in Edit mode. It can be applied to specific parts of the mesh using vertex groups.
- Subdivision Surface – Catmull-Clark subdivision produces smooth results. Sharp edges can be defined with subdivision creases or by setting the Sharp flag of certain edges and adding an EdgeSplit modifier (set to From Marked As Sharp) before the Subsurf modifier.
- EdgeSplit – This modifier can also be used alone, having then a bit the same effects as the Auto Smooth tool. But it still modifies the mesh geometry, as it duplicates all edges marked as Sharp and/or “really” sharp (i.e. between two faces highly angled).
