Gimp doesn’t really need any introductions, it is usually touted as the Photoshop “alternative” for Linux, and is included in a lot of Linux distros. It is the closest thing you will get to Photoshop. To use it professionally, you will probably need to add some plugins and 3rd party applications. All in all, Gimp vs. Photoshop debate usually stirs lots of controversy, with neither sides arriving to a decisive conclusion.
Krita is part of the Koffice suite, the official suite for KDE. Its design emphasizes creating new images as opposed to manipulating existing photographs. Krita’s README file states:
Krita is a paint application for raster images. It’s also, according to the Dictionary of Phrase and Fable:
The first of four Hindu periods contained in the great Yuga, when the genius of Truth and Right, in the form of bull, stood firm on his four feet, and man gained nothing by iniquity. In the Mahabharata, the name ‘krita’ is used in a context where this can be translated with ‘perfect’ – the perfect age. Krita is Swedish for chalk and rita means “to draw”.
Kolourpaint provided the basic functionality of Microsoft’s Paint program with additional features like transparency. It is geared to the average user, nothing too fancy.
Gimpshop is a modification of the Gimp and intends to replicate the feel of Photoshop. According to the developer:
“My original purpose for GIMPshop was to make the Gimp accessible to the many Adobe Photoshop users out there. I hope I’ve done that. And maybe along the way, I can convert a Photoshop pirate into a Gimp user.”
While Pixel isn’t Open Source nor free, it is a valid option since it has a native Linux version and comes for the cheap (only $50). I read a lot of people comparing it to Photoshop, so it might be worth taking a look at. You can download it for free as a trial before you decide to fork out $50 :).
Adobe Photoshop CS2 on Ubuntu from justmoon on Vimeo.
While I don’t recommend it, but if this is the only way you will consider making a switch, then by all means do :).