GIMP Plugin Registry

Sharpening tool, uses blurred mask. Sharpness is modified with few sliders that work like a kind of equalizer. User can control blurring parameters (radius and treshold for selective blur mask). It provides 4 types of output: Sharpenned image, mask, split/comparision mode and mask-to-img differences.
Brightness of image can be affected by levels-like tool that works indirectly - via the mask.
See attached screenshot for more info.

Plugin is multithreaded.

Downloads (source code with instructions for linux) and few sample images http://code.google.com/p/aumask/wiki/Introduction.  read more »

script-fu-simple-contrast-mask adds a contrast mask layer above the current active layer. A contrast mask brightens the dark parts of an image and darkens the bright parts. This serves to enhance details.

The script is called "simple" because it does not ask any questions. It assumes defaults for all parameters. Specifically, the radius for the Gaussian blur is set to one percent of the shortest dimension of the image (width or height). The user can adjust the blending level after creation by adjusting the opacity in the layers dialog.  read more »

EAW Sharpen is a filter which sharpens an image without annoying halos.
It's based on Mikes Python plugin:
http://www.mm-log.com/blog/2010-04-05/gimp-edge-avoiding-wavelets
More info about the algorithm from Raanan Fattal:
http://www.cs.huji.ac.il/~raananf/projects/eaw/index.html  read more »

The script enables you to do two image adjustment operations to all images in a folder:

1. Individually adjust the color balance in shadows, midtones and highlights
2. Adjusting the Brightness and Contrast

You choose a folder with a folder browsing widget, you can also specify the file extension of the files you would want to change(useful if you have non supported files in the same folder).  read more »

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.

What is Color Spotter? Basically, it's contrast, but "centered" around a color. Another way to see it is as another "Color selection" tool: you specify an image, a kind of threshold, and it selects color that are close to the one you specified; only, Color Spotter keeps every pixel from the image, darkening the wanted colors, brightening the others.  read more »

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!

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.  read more »

This plugin is not more maintained but still works very well On Gimp 2.6 and even 2.7
Was developed by Peter Heckert , Windows binary were provided by Michael Schumacher.  read more »

Fresh Windows compilation of Gimp ace2 (Adaptive Contrast Enhancement) plugin. 50 Kb exe, 20 Kb zip. No console window.
[Image]/Filters/Color/Adaptive contrast