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 (with the exception of Meet the GIMP).
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.
I've also re-designed this page and tried some new things out (a little bit hackish) - so let me know if something is wonky for you. I have also removed ads and the sidebar to make this page layout a bit cleaner for everyone. If you are one of those cool froods who were nice enough to visit an ad now and then - click on them on the tutorial page instead... :)
★ 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)! Polaroid 600 Film Border Script As a companion to the Expired Polaroid 600 Film Effect, I also wrote a script to automate the process of creating a more realistic looking border. Curves and Color Toning Using the Curves dialog to color tone your images, and how to approach it in general. More Color Curves (Skin) More in-depth look at approximating colors and tones from other sources (like other photos or images). Black and White Conversion (Part 1)(Part 2)(Part 3)(Part 4)(Part 5) A (hopefully) comprehensive look at methods for creating high-quality grayscale images. Including combining the methods for an overall workflow.
★ 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. True Pseudogrey in GIMP How to encode more than 256 shades of gray data in a pseudo-grayscale image. Up to 1786 values of gray. (Includes Script-Fu for automatic creation of Pseudogrey images). Heal Selection (Resynthesizer) GIMP has had a "Content Aware Fill" for years before Adobe tried it. See how to use the Heal Selection filter to remove objects from your images.
Calvin Hollywood Freaky Details Artist Calvin Hollywood produces some neat, gritty images using this technique to enhance details. It's now possible to do it in GIMP!
Open Source Portrait (The Shoot) (Postprocessing) A complete portrait workflow, from setting up the shoot through all of the post processing (includes source files)
Blue Channel Check LayerUsing an images blue channel to bring out imperfections for retouching.
Making Babies FlyAn old tutorial showing how I composited my daughter to look like she was flying!
★ OTHER SOFTWARE ★Focus Stacking Macro Photos (Enfuse) How to use the open source Enfuse to fuse focus stacked macro images and increase depth of field!
Median Blend Noise Reduction Removing noise from your images with multiple shots and Imagemagick/GIMP/G'MIC
HDR Photography with LuminanceHDR Using LuminanceHDR to create and tone map HDR images, and looking at all of the tone mapping operators