what specification for jsTree node icons?

I want to create my own node icons for jsTree application. A jsTree sample could be found here

I 开发者_C百科want to know what specification the new icon has to have

• size
• transparent?
• could you recommend any program (mac or pc)
• anything else I forgot

Bit of a weird question, but anyway:

The icons are individually 16x16.

All the icons are inside one .png using alpha transparency (the background).

The CSS Sprites technique is being utilized: http://static.jstree.com/v.1.0pre/themes/default/d.png

Which image editor to use?

I'd use Photoshop, but any image editor that can handle .png's alpha transparency will work.

Try: https://superuser.com/questions/25451/looking-for-a-good-free-image-editor