Any serious skinner needs a graphic design tool with certain capabilities in order to take the design files and assemble them into a finished web site. In particular, layers and the ability to slice pieces of a design and export those pieces are essential. Layers allow a themer to hide pieces not needed in a finished CSS theme, such as text that will eventually become real HTML on a page. Slices, meanwhile, are the pieces of an overall design that are exported during the layer manipulation process. They are the images the end user eventually sees on the rendered page. This is different from cropping, which actually alters the size of the canvas; slices are just pieces of the overall design, cut with precision, exported, and then manipulated with CSS.
The most commonly used graphic design tools used for web design are Adobe® Photoshop®, Adobe® Fireworks® (formerly Macromedia) tool, and open source tools such as GIMP. It is not generally recommended to use tools such as...