In this tutorial, we'll be designing a simple pixel filter: that is, each transformed pixel depends solely on the corresponding source pixel. That saves us from having to deal with border conditions and/or row/column decomposition, which are too complex for a simple tutorial. We'll be starting with a simple filter that boosts green and dims blue, and work up to a filter that supports 2x horizontal enlargement, user configuration, MMX speedups, and script (job control) support.

This filter has a very simple algorithm that will be covered in the next part. Generally, though, before writing code for a filter you will want to verify that the algorithm you have is correct beforehand, because once a filter is running and optimized it's very difficult to make changes at the algorithmic level.