This filter decomposes the active layer or selection into several layers, named 「scales」, each of them containing a particular set of details. Finest details are in first layers and they become larger until you get to the last one, at bottom. This last layer is called 「residual」 and holds what is left after all detail layers have been removed; it represents the global contrast and colors of the image.

Each of scale layers are set to combine using the Grain Merge layer mode. This means that pixels that have a 50% value will not affect the final result. So, painting a wavelet scale with neutral gray (R:50% G:50% B:50%) will erase details.

Wavelet-decompose is a wonderful filter for skin smoothing and retouching, removing blemishes, wrinkles, spots from your photos. It can be used also for sharpening and local contrast enhancement and for removing stains, colors, tones. All this is well explained in tutorials mentioned above.

This filter is found in the image window menu under Filters → Enhance → Wavelet decompose.

Scales: Default scales number is 5. You can increase it to increase scale fineness.

Create a layer group to store the decomposition: layer groups are treated in 「レイヤーグループ」.

Add a layer mask to each scale layer: layer masks are treated in 「レイヤーマスク」.