GIMP - GNU Image Manipulation Program

An open source photo editing tool. A quirky interface (in Windows) but otherwise very solid. Great feature set.

OT: https://krita.org/en/ - claims non destructive effects

http://gimp.org/
A nifty plugin. (actually, it's now part of Gimp, just hard to find in the dialogs. It DOES work nicely to turn anything into a texture that tiles nicely. This will create tileable graphics. I.e. they look pretty when set as a background and repeated horizontally and/or vertically.
http://www.csse.monash.edu.au/~pfh/resynthesizer/
An online version of a book for using gimp. Seems pretty good.
http://gimp-savvy.com/BOOK/

Personal tricks used:

Nice fade to another color - Use gradient and Foreground to Transparent and do little steps.
Highlight text (of a screenshot) - http://www.sitepoint.com/forums/showthread.php?t=604174 - Select the area of text you want to highlight. Create a new layer. Fill the selection with yellow. Set layer blend mode to multiply.
Brighten a portion (e.g. person) in a photo - Make duplicate layer. Add layer mask (filled w/white) to upper layer. Curve the top layer to whatever you want. Use gradiant black to transparent to gracefully blackout parts of the upper layer (to mask out the brightened parts that you didn't want to brighten).
Clone tool: http://docs.gimp.org/en/gimp-tool-clone.html - It's the "stamp" looking one. Hold ctrl+click to set the source. Click elsewhere to stamp. Alignment = fixed doesn't shift the original stamp source; other alignments do.
iwarp - deform parts of image

Related: Krita is an OSS painting program.

tags: image, graphics,