Bump Maps - Additional Information
The Auto Bump Map option on the Material Wizard creates a bump map (automatically) from the SketchUp image on a material.
Auto Bump Map Sample
Here is an
example of a wall with SketchUp's stone material, and two spot light shining on the the material:
(Bump maps have their best effect when there is lighting at an angle to the material, because the bump map 3D effect is more pronounced when there is light shining on the material.)
Bump map guidelines
A bump map uses the intensity of the raster image to determine a height offset from the base face on which the bump map is placed. (Black is the lowest elevation and white is the highest.) The bump map is used to alter the effects of lighting on the surface, which gives it an enhanced 3D effect, without having to model the geometry in 3d.
Basic bump map
This is a simple bump map, with a flat area in white, and a hole in black. There are several gray transition lines between the white and black areas.
See: No transitions for an example with no transition lines.
This is a bump map used for a brick effect. (The color will be added when the texture is created in SketchUp.)
(Note: This image, which was downloaded from the internet does not have any transition gray. It jumps from light to dark. The Renderer will add some transition if not is provided in the raster image.)
This is the "flat" rendering in IRender.
(No bump effect)
This rendering is made with the same SketchUp material, and the bump effect enabled ("_bump" added to the material name.)
This gives more of a 3D effect. (The light and dark shades at the edges of the bricks are determined by the angle to the sun in the actual model.)
No gray transitions
This is the same image with the gray transition lines removed. The only colors are black an white.
The IRender engine adds some transition, but does not do it as smoothly as when transition lines are included in the raster image. But notice, there is some distortion on the corners.
Reversed bump map with no transition lines. The black area in the image appears to extrude out from the surface.
Shaded bump maps
Bump maps should not contain shading from the light. (For instance, a photo of a stone wall will have dark areas because of lighting, rather than because of the depth of the surface.
This rendering on the right is a "flat" rendering of a SketchUp stone material.
However, because images such as this stone image tend to be darker between the rocks, they do make good, (even if not technically correct) bump maps.
Better stone example
Bump maps can be used to provide some 3D effect to renderings without having to complicate your model with lots of 3D geometry.
However, the bump maps do not produce true 3D. They are used for lighting, but not used to obscure other geometry.
Also, bump maps work best when there is good angled light to bring out the bump effect.
Note. This concept - using an image to create a bump map of itself is not really correct. It make the dark parts of the image seem depressed and the light parts raised up. However, many people and many rendering systems use it because it create a 3D effect for some materials.
Here is a better example, using a depth oriented bump map, rather than just an image to create the bump effect.
users can create more advanced effects by applying bump maps to nXt materials. (For example, using one raster image for a bump map and another raster image for a texture.) See:
IRender nXt Bump Maps
For more information on Bump Maps: