contrast

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.

Color Spotter

juef — Thu, 17 Sep 2009 04:22:11 +0200

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.

The best way to understand is to see it in action:

Here, the selected color was from a pixel from the plantpot (beige-ish).

This plug-in was mostly an experiment for me: you could say I made it just to get familiar with programming C plug-ins in GIMP. I have another plug-in I want to make, but as it's much more complicated, I wanted to make sure I could deal with the basics first.

Suggestions welcome! Thanks for reading, hopefully this will be useful to at least one person :)

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!

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.

UnsharpMask2.0.12 (Windows binary -source code)

PhotoComiX — Mon, 16 Mar 2009 06:00:38 +0100

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. but the original side is offline from years and all old links dead

i am mirroring both source code and binaries to avoid it can get lost and i repost here also in the hope that may found more users and a maintainer (as i said still works very well ,from gimp 2.0 till 2.7 a maintainer may help for the future )

About the most obvious question, what is the difference with standard unsharp mask that is simple,
what gimp USM offer is a only a subset of what this plugin may do.

gimp USM works ,basically by adding a blurred duplicate ,that as result create a white halo around contour's edges.

As example if you have a black arrow on dark grey BG, a more or less wide white halo around the arrow will made it much more visible and the image more sharp
But that easily lead to effect similar to overdone HDR and work better on the darker part of the image to reveal less dark details

Well USM2 may do that but also the contrary, sharpen by adding a dark halo
To use a similar example may sharpen a gray arrow on a white BG by creating a dark halo around arrow's contour

"Dark halo" sharpening on photos look often more natural then white at the most usual settings,
while pushing for dramatic setting is usually a more pleasant and artistic effect,
( we are used to accept black outlines as in draw,comics, illustration, so are more acceptable for our eyes then white outlines ..
Note that a thin but very intense white halo around contours edges is identical to white outlines, as a thin and very dark halo is identical to black outlines ..this is relevant for "artistic" or "creative" uses )

Interface may look too complex at first but just draw a ideal line under the 4th slider will solve

All what up is "BASIC" : on 4 sliders there 3 correspond exactly to that of the Gimp USM
"+" is to regulate the "white halo sharpening" ,"-" to regulate the "dark halo sharpening"
(NOTE: If both"+" and "-" are set to 0 then plugin do not sharpen but create a gaussian blur )

All what after that ideal line is "ADVANCED" ...default is fine in most cases anyway from there you may correct the gamma, or dose the intensity of the effect differently on shadows, middletones and highlights.

More accurate information are included in the zip.
#####################################################################
If someone may provide a better description is welcome , i am a user and not a developer and my English is quite approximate.

DOWNLOAD
http://photocomix-resources.deviantart.com/art/Lost-Found-Gimp-UnsharpMa...

Gimp ace-0.6.7 Win32

Francois_C — Tue, 18 Nov 2008 08:22:11 +0100

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

D-Dayed

tuxcomputers — Sat, 14 Jun 2008 10:36:31 +0200

D-Dayed is a script for The GIMP
Makes the image like the over saturated grainy war photos as evoked in the cinematography of films like Saving Private Ryan

Orton Effect

Uuner — Mon, 21 Apr 2008 00:56:52 +0200

This script simulates Orton slide sandwich technique (mixing blurry and sharp versions of the original image).

Contrast Fix

Darla — Wed, 23 Jan 2008 12:51:16 +0100

Adds a Contrast Adjustment layer to your image to help fix contrast problems.

Guide to Using the Contrast Fix Script