This chapter will describe in detail a fully functioning, but simple OFX image effect plug-in that inverts 8 bit RGBA images. It gives a flavour for how the API operates and some of the components in it. The source will be broken down into sections and each one explained as we go along. The code is actually C++, but it uses the raw OFX API. The code is not meant to be perfectly optimised example of how to write an image processing effect, but rather as an illustrative example of the API.