enhance

Cheap HDR

theilr — Thu, 12 Nov 2009 05:05:32 +0100

Provides a kind of poor-man's HDR (high dynamic range). It doesn't actually increase the dynamic range; in fact, it decreases it, overall, but in a way that maintains local contrast. But this gives you some headroom to increase the contrast of the image overall, thus enhancing the local contrast.

Fix Overblown Areas

gfxcoder — Mon, 06 Jul 2009 22:25:17 +0200

This script helps fix overblown areas of an image. It's not as good as some other methods that must be done manually, but it's not bad. It will NOT fix clipped colors (maximum overblown areas); it only helps increase the contrast in bright highlights.

The script is located in "<Image> / Script-Fu / Enhance / Fix Overblown"

Feedback welcome!

Clean CCD Noise

gfxcoder — Mon, 06 Jul 2009 01:28:05 +0200

This script helps fix noise found in digital camera pictures.

Important:

G'MIC must be installed! When this script calls up the G'MIC plug-in, select Bilateral Filter with default settings.

There seems to be some confusion as to what all this script does... So here's a short description of the procedure:

Duplicates the active layer
Calls G'MIC plug-in (requiring user to select the Bilateral Filter with default settings, then OK'ing)
This layer is duplicated (saved for later)...
The layer is subtracted from a copy of the original layer and ran through curves-spline to increase the contrast at the lowest end
Finally, this layer acts as a alpha mask for the original copied layer (from above)

The subtracted mask tempers dark spots found in browns (wood, some skin, etc). This is found with red / green highlights in the brown to begin with.... I believe.

Version 1.1 (2009 July 06)

Tempered darkening noise found in browns (wood)

Feedback welcome!

The script is located in "<Image> / Script-Fu / Enhance / Clean CCD Noise"

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.

Maximize Local Contrast

Roy Johnson — Wed, 01 Jul 2009 18:36:27 +0200

FX-Foundry/Photo/Enhancement/Maximize Local Contrast... Like Stretch Contrast, but instead of using the minimum and maximum pixel values from the entire image, uses the minimum and maximum in the vicinity of a pixel to compute its new value. Takes a while to run, but really brings out textures. Result is a Grain Merge layer that adjusts values of the original image.

This filter operates on the visible image, not on a layer or selection.

Radius indicates how wide a pixel's influence is. If you choose too small a value, adjustment will be too localized and the image will look patchy. Larger values take a bit longer to run.

Threshold indicates how many neighboring gray values above and below a value can be treated as the same, in finding minimum and maximum values. Purely a speed trade-off. Using very low values will make it very slow. Too high values will cause visible "steps" in color values. The latest version does not include threshold, but the older version is still available.

"Feather Haloes" helps smooth out haloes around high-contrast areas.

"Keep Min and Max Layers" leaves the intermediate layers in the stack so you can look at them if you're interested.

Update (21 Jul 2009):

New algorithm that works right without any compromises for speed. No scaling, no threshold. It does take a bit of time on large images; 45 seconds for a 1500x2000 pixel image on a modern but not especially powerful PC. The full 8-megapixel image took about 3 minutes. Most of the time is spent on grow-selection, so don't be alarmed when the progress meter seems to hang up for a while. There are just two grows and two feathers to do.
If you want a speed compromise, I've added Scaledown factor, which will reduce the time spent in selection a lot, but will add some time for scaling the image. There's essentially no loss of quality. Recommended for especially large images.

Updates (13 Jul 2009):

SPEED! Mapping of Min and Max is done on scaled-down layers. Now even large images can be done in reasonable time.
Feather haloes feature for more reasonable results on high-contrast images and images with big flat areas
Layer mask keeps narrow-contrast areas under control

Updates (9 Jul 2009):

Fixed the bug that left strange artifacts in the image.
Changed radius to work as a % of image size (maximum dimension)
Increased feathering and added limits to min and max layers to control haloes around small, high-contrast features
Got rid of sample images. Will find better examples.

Blend Removal

das — Wed, 14 Jan 2009 18:09:03 +0100

This is simple plug-in computes original image from merged image and upper (halftone side) image. It is useful for removing semitransparent mark or frame based motion blur.

G'MIC plug-in

dtschump — Tue, 13 Jan 2009 14:16:31 +0100

The G'MIC plug-in for GIMP defines a set of various filters, including artistic filters, image denoising and enhancement, 3D renderers, etc.. It is a quite large plug-in, integrating a lot of different effects to apply.

This plug-in is able to update his list of filter definitions from the Internet (so it improves itself over time), as well as allows any user to add its own custom filters in it.
It has been written by the author of the GREYCstoration algorithm (used for image denoising). It is actually intended to replace it in a near future.

Download G'MIC for Windows 32 bits

Here is one screenshot of the plug-in in action, as well as a result of filter application :

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 Sharpen-0.1.1 Windows 32 binary

Francois_C — Mon, 12 Jan 2009 14:26:09 +0100

A new Windows compilation of the last version of this fine plugin written by Marcor.
No console window. Compiled with LDFLAGS=-mwindos as usual.

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.