Krita is a painting and image editing application. 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
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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!
Krita can import RAW images in 8 and 16 bits per channel and load and save the usual image formats: tiff, png, jpeg.
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. [Less]