Intarsia and segmentation are two very similar processes, but with one very important difference.  They are both usually cut from 1/2" to 3/4" solid wood.  They are then shaped by sanding or carving to get a 3D effect.  This 3D effect can be enhanced when the pieces are glued together by shimming some of the pieces.  The difference between the two methods comes in how the project is "colored".  In segmentation the individual pieces are cut from the same piece of wood and then painted or stained before the pieces are glued back together.  With intarsia each different color is cut from a different kind of wood.  Therefore, the cutting of an intarsia project needs to be much more precise than any other kind of scroll saw work, because a piece that was cut from walnut may have to match exactly with a piece that was cut from popular.