Which Unix tool for Pixel-art -generation?

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http://unix.stackexchange.com – I have had problems to generate pixel art for a game where units are of specific sizes such as 55x55 (not geometry but by pixels i.e. 55 pixels by 55 pixels). I have tried Gimp where I have misread many-times the sizes with the select tool -- it is irritating to get a bit too distorted size. Then I have used Inkscape that works actually quite good -- you generate the vector-image and select it and then you go to "Export to bitmap" where you can specify the size (this same feature is probably also in Blender, probably as easy). Anyway I am looking for something more powerful like having helper (HowTos)