decomposition

Separate Luminance

Roy Johnson — Thu, 02 Jul 2009 18:43:26 +0200

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. Most of the time, it will be un-noticeable, and even when it is, it shouldn't make any real difference. If you want to be sure your Lum layer is pure luminosity, you can check Excess color on separate layer. When merging, always merge onto the Lum layer rather than merging the two color layers together.

Wavelet Decompose Script-Fu

christoph.traxler — Sat, 17 Jan 2009 16:12:58 +0100

This is a Script-Fu script for losslessly decomposing an image into different detail scales. This should be useful for photo post processing (for instance reapairing skin in portraits).

I first saw this function on the plugin "Wavelet Decompose" by marcor. (http://registry.gimp.org/node/11742 - This is also a good description on how image manipulation can benefit from wavelet decompositing.) I believe the Script-Fu script produces very similar results to marcor's plugin. (I did not use marcor's plugin for myself, so I can't really tell. But the description on the plugin is very good and I used it as a reference.)

Unfortunately I'm not familiar with installing plugins on a Windows system. But I wanted to use a wavelet decompose function on my Windows system. As I also wanted to learn Script-Fu, I thought it would be a cool idea to write a wavelet decompositing script by myself. It would also be a good reason to practice Script-Fu.

So this is my first Script-Fu script and I hope also useful submission to the GIMP registry. (At least for those who are not able to install Plugins on their Windows systems ;-P)

After installing this script (copy to your scripts-directory), you should find a new entry "Wavelet Decompose ..." in your Image-menu.

Maybe this script also runs on GIMP 2.4 or older versions. But I was testing it only on version 2.6. Please write a comment, if you ran the script on 2.4 or older without errors. Thank you!

Description on the parameters:

Minimum Scale:
Enter the pixel size of the smallest Scale (Scale 1). For instance the default value "1" shows only the sharpes available details on the Scale 1 layer. Enter higher values if you work on higher resolution photos.

Scale Count:
Enter how many layers of detail scales you want.

Scale Increase Factor:
This tells the script how many times the next scale should be larger (showing rougher details) than the previous.

Scale Constant Increase:
How many pixels should the details on the next scale be rougher than the previous scale.

Work on Copy:
This option creates a new image. If you disable this option the original image will be flattened and then the decomposition is done on the original image.

Wavelet decompose 0.1.2 Win 32 Binary

Francois_C — Mon, 12 Jan 2009 14:54:41 +0100

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

Wavelet decompose

marcor — Tue, 18 Nov 2008 17:18:44 +0100

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.

Wavelet scales

An image can be transformed into a set of wavelet scales. There are detail scales and one residual. The detail scales contain the image details of a their scale size. This means that scale 1 contains only image details of the smallest scale. Scale 2 details are larger and scale 3 details even larger (and so on). This image illustrates this:

This plugin computes these scales losslessly and creates a new layer for each one. The recomposition is the addition of all scales which is done by GIMP using the grain merge layer mode. You can then paint the scales with your favourite tool, using (128,128,128) as neutral colour (for the details, not the residual). Values below neutral darken, values above lighten. The most straightforward thing to do is to use the paintbrush tool with the neutral colour and use different brushes and opacities. That way you erase details.

Skin retouching

The problem with skin retouching is retaining skin detail but erasing spots and such. However, one might want to keep freckles in the face (see image below). Achieving this is very difficult when operating in the normal image space. The skin details such as pores and hair are very small, spots and pimples are larger. If you erase the larger spots (with an airbrush for example) you hide the skin details inside it. With wavelets you decompose the image into scales of different detail size. To state it simply: One scale will contain the skin details like pores, other scales contain spots. They are rather nicely separated. Look at the image with the wavelet scales above. The first scale contains pores and freckles (it's a small image indeed) and the second and third one the spots. The problem is not separating the details from the spots anymore but finding out in which scales they lie. This image (taken by +psv) has been edited using wavelet decomposition. One could have erased the freckles easily, but this natural face is beautiful because of them.

Noise reduction

The human eye easily distinguishes noise from image detail. Computers cannot. By decomposing the image into wavelet scales you can decide for yourself which parts are erased and you get the most high quality result. For example in image regions which are out of focus you know there can't be any image details on the pixel size (they are just blurred). So you can pick a brush and erase wavelet scales 1 and 2 in such places. Image details of greater size are untouched by this as you will notice.

Local contrast

If you change the residual scale instead of the detail scales you can change the brightness of the image or global contrast without affecting local contrast. This means that you can get image details back out of dark image areas in full local contrast. This works for overexposed areas as well. However clipped image details (beyond white or black) cannot be restored.