Overview of Lua Filter Scripts
A Lua script filter in TwistedBrush is a small piece code written in the Lua programming language (versin 5.1) that can be used to quickly implement image processing filters right within TwistedBrush.
The Lua scripting filter is designed to be somewhat compatible with the gluas plug-ins used in The Gimp image editing software package. The gluas plugin system was developed by Øyvind Kolås. There is a nice tutorial of gluas titled Image Processing with gluas a large part is applicable to TwistedBrush and most (if not all) of the sample scripts shown should work within TwistedBrush.
An excellent online book covering all the details of the Lua programming language can be found here.
In case you haven't determined this yet, this topic and programming of filters with Lua is designed for those with computer programming experience. However, this doesn't limited anyone from using filters that are either included with TwistedBrush or shared from developers.