Gimp is a free photoshop replacement.
Yup. Free as in no cost and Free as in Freedom.
It’s easy to add to Ubuntu through the Synaptic Package Manager that comes with Ubuntu (found in System=>Administration). It can also be downloaded and added manually for Linux, Windows, and Mac.
I have not used all of its features because I use it for basic photo enhancements (cropping, adjusting levels, resizing, setting filters…) and for creating images to be used for icons, banners, etc… It’s easy to learn to use, pretty intuitive and when you need help, just click on help or look through the easy to navigate user manual, available in many languages.
Here are a list of some features, from the site:
Features and Capabilities
This is only a very quickly thrown together list of GIMP features. You can also have a look at the illustrated features overview.
o Full suite of painting tools including Brush, Pencil, Airbrush, Clone, etc.
o Sub-pixel sampling for all paint tools for high quality anti-aliasing
o Extremely powerful gradient editor and blend tool
o Supports custom brushes and patterns
o Tile based memory management so image size is limited only by available disk space
o Virtually unlimited number of images open at one time
* Advanced Manipulation
o Full alpha channel support
o Layers and channels
o Multiple Undo/Redo (limited only by diskspace)
o Editable text layers
o Transformation tools including rotate, scale, shear and flip
o Selection tools including rectangle, rounded rectangle, ellipse, free, fuzzy
o Foreground extraction tool
o Advanced path tool doing bezier and polygonal selections.
o Transformable paths, transformable selections.
o Quickmask to paint a selection.
o A Procedural Database for calling internal GIMP functions from external programs as in Script-fu
o Advanced scripting capabilities (Scheme, Python, Perl)
o Plug-ins which allow for the easy addition of new file formats and new effect filters
o Over 100 plug-ins already available
o Load and save animations in a convenient frame-as-layer format
o MNG support
o Frame Navigator (in GAP, the GIMP Animation Package)
o Onion Skin (in GAP, the GIMP Animation Package)
o Bluebox (in GAP, the GIMP Animation Package)
* File Handling
o File formats supported include bmp, gif, jpeg, mng, pcx, pdf, png, ps, psd, svg, tiff, tga, xpm, and many others
o Load, display, convert, save to many file formats
o SVG path import/export
* Much, much more!