There are a ton of tutorials already available on the internet for using GIMP to do different things (heres some from gimp.org, Gimptalk, and Meet the GIMP for example). I noticed that though many of these tutorials are great, they didn't necessarily meet my needs for wanting to do high quality post-processing of my personal photos.I've cobbled together a handful of techniques for photo retouching, and thought I would try to share some of them with everyone here. Mostly they are aimed at photo retouching and manipulations as opposed to some of the other (wonderful) things GIMP is capable of doing.
Getting Started
The Interface
An introduction to the GIMP interface and where things are laid out.
New Layer
Adding a new layer to an image, and some layer basics.
Adjusting Levels
The basics on using the Levels tool to adjust relative values in an image (helps with washed out images).
Color Correction
A method for color-correcting a photo using Colors → Threshold to determine pixel values. This is the method I use first before anything else is done to an image.
Layer Masks
An introduction to the use of layer masks to control a layers transparency. Including a short how-to on selective coloring an image using these masks.
Color Effects
Muted Colors
A look at a couple of different options for muting the colors in a photo using desaturated layers, layer blending modes, and color curves. BONUS - my very first script-fu to automate the process!
Expired Polaroid 600 Film Effect
After becoming enamored with expired Polaroid 600 film, I set out to emulate the effects in GIMP. Including a script-fu for automatically applying the effect to your images (and color curve presets for the film as well)!
(Slightly) Advanced
Luminosity Masks (and Split Toning)
Creating and using Luminosity Masks in GIMP for incredible control over different tonal ranges in your images (also, a small split toning tutorial as well).
Contour Painting (a Pinup!)
Utilizing Dodge & Burn techniques to paint contours onto a subject for stylized or subtle enhancements to an image.
Skin Retouching (Wavelet Decompose)
How to use the plugin Wavelet Decompose to be able to edit skin in the frequency domain with unparalleled control! An incredible method for skin retouching.
