GIMP Plugin Registry

FX-Foundry/Color/Separate Luminance...

Creates two new layers: one containing the Luminance, and the other the Chroma information in the form of a Grain Merge. Optionally, it will color-enhance (maximize saturation in) the Chroma layer while still keeping it luminance-neutral.

This allows you to do noise-reduction and sharpening on the two layers separately.

Update (23-Jul-2009):
Noticed that highly-saturated colors exceed the ability of the grain-extract/grain-merge to handle without clipping the color, so I have made the excess color get folded into the luminance layer.  read more »

Windows 32 binary of the last version of this plugin written by "wavelet" Marcor ;)

This plugin losslessly decomposes a layer of an image into layers of wavelet scales. This means that you can edit the image on different detail scales (frequencies). The trivial recomposition of the image can be done by GIMP's layer modes so you can see the results of your modifications instantly. Among the applications are retouching, noise reduction, and enhancing global contrast.  read more »