Make sure that the RGB color underneath transparent sections does not turn black or white! Some image editing programs (in particular Photoshop) will lose the color beneath a transparent area.
With a normal map, this is very bad - black and white are not legitimate normal map colors, and the result will be bogus normal vectors under the non-shiny part. Normal maps affect more than just specular shiny hilights - the normal map affects all lighting, so having black or white under your transparent (non-shiny) parts is bad news.
To check whether this has happened, I recommend Graphics Converter, which will show you your alpha and RGB channels separately, exactly as they are in the file.
Make sure your RGB value are normalized. The "length" of the normal (as encoded in RGB) must come out to a distance of 1. This is virtually impossible to do using PhotoShop or an image-oriented program...I suggest you use a real plugin to PhotoShop or Blender to create normal maps that are correctly "normalized".
Friday, August 28, 2009
Two Warnings About Normal Maps
Two warnings about normal maps: