How to load BYTE values

A simple question: how can I load BYTE values (e.g. some graphic-files) form one (or more) files into a table without using an externel program? The manuals says, that the BYTE-data must be in ASCII-hexadecimal form. I tried it with "od -h", but it wasn't the right format. So how to manage it in a comfortable way (script) ? Olaf Hendel