STEPI.EXE is a command line graphical utility for the conversion of a Windows 16 colours image into VZ's four colours.
However, it also allows for "BPOKE" commands for the use in C with the Z88DK kit.
It also allows various other dumps (defb for asm, include files) along with the VZ's representation of graphical data.

Basically: It converts a RAW exported image from a fancy graphical package into a VZ MODE(1) format and does all the nibbling 2byte-per-colour conversion.
This program is a hack of a hack of a hack, and is not fancy at all, and will most likely disappoint you.
It was written by Dave for Dave to do his dumb graphical stuff. Included in here for completeness.
Dave. 12/Nov/2019