This is one of over 4599 effects generated by Filter Forge, a Photoshop plugin that allows you to create your own filters.
To open this filter, you must have Filter Forge 1.0 or higher installed on your computer. If you don't have it installed yet, click here to download Filter Forge
This is a simple colour processing filter that takes the shadows, midtones, and highlights of your image and assigns them to one of four colours. At low "Colour Smoothness" values, the results can look like poster art using process colours (e.g. Pantone, Toyo, ANPA). Higher values can approximate the look of a more sophisticated quadtone or produce effects that simulate cyanotype or sepia.
posterization quadtone process_colour scarykitty cyanotype sepia pantone