A general purpose high-pass filter plugin. It shows up as Filters->Generic->High Pass Filter. You can select a blur radius that sets the size of detail to be passed by the filter, a contrast adjustment, as well as an option to keep the source layer or replace it. It actually implements 5 different high pass modes: 1. Colour - I think this is the same as photoshop's high pass filter effect. 2. Preserve DC - like colour, but adds the average image colour back in. 3. Greyscale - this desaturates the layer before high pass filtering. 4. Greyscale, Apply Chroma - as above, but blends it in with the source layer colours 5. Redrobes - (named after the technique described by Redrobes)