Cyanspews

Hello all, I myself am not a modder, but i modify mods to a minor degree, and there are some mods with just the worst pipboy icons, so i know it's pretty simple, get the mod, make a new image, convert it to the proper file, and replace the original, but everytime i do (using png format and transparent backround) the image gets stretched and the backround is full black, so i'm wondering what optimal image size and settings i should use for modding icons, thank you.