HiRes test which takes a black and white 256x192 image and displays it on a real ZX81. This was done by writing a Java based tool that reads in a bitmap and finds the closest bit pattern matches for that image with the ZX81 ROM.

It then generates an index into the ROM and an array of bytes which represents the HiRes screen 

The source is available on github and the .p file can be downloaded from here. The source code of the main file (hires.asm) is listed here