Krita is a painting and image editing application for KOffice. Krita is part of KOffice since version 1.4.
Krita contains both ease-of-use and fun features like guided painting (never before has it been so easy to airbrush a straight line!) and high-end features like support for 16 bit images, CMYK, L*a*b and even OpenEXR HDR images.
Krita supports many managed colorspaces, like rgb, grayscale, cmyk, lab, ycbcr and lms, in 8 and 16 bits per channel. Some colorspaces even support 32 bits per channel!
With the development of KOffice 2.0, all these colorspaces will be available to all KOffice applications that need color management. An experimental watercolor colorspace that tries to follows the physics of paint is included in 1.5.
Krita can import RAW images in 8 and 16 bits per channel and load and save the usual image formats: tiff, png, jpeg. Other image formats, like xcf, can be imported and sometimes exported through the GraphicsMagick import/export plugin, but are not fully supported.
Krita has a large array of tools. The 1.6 release contains freehand, line, rectangle, ellipse, polygon, polyline, star, bezier curve, duplicate, paint-with-filters, crop, move, transform, perspective transform, contiguous fill, gradient, text, color picker, pan, zoom, perspective grid, selection paint, selection erase, rectangular select, elliptical select, polygonal select, contiguous area (magic wand), outline, magnetic selection, bezier curve select and select by similar colors.
All paint tools can be used in soft brushes, hard pencil, airbrush or eraser mode. SIOX-like foreground extraction is in the works.
Krita has image layers, group layers, adjustment layers and the innovative part layers: any KOffice document can be embedded as a layer in Krita.
Krita is scriptable in Python and Ruby and offers a small, but useful DCOP interface. Krita 2.0 will also be dbus-enabled.
There is a rich set of filters for image enhancement, color enhancement and artistic reinterpretation of your image.
Krita is a very modular application and if you want, you can easily extend Krita by creating new tools, paint modes, filters, dialogs, colorspaces and import and export filters.
Most of these plugins are described in the "Developing Krita Plugins" document. Krita also has an extensive user manual.