Thanks to javl from the the forums for sharing this tool with us! They write:

In some of the display tutorials (such as this one) there is a short how-to on creating bytearrays from monochrome images using the Windows based “LCD Assistant”. I didn’t like having to boot a virtual machine to create images, and also I didn’t like the program itself (got some errors and flakey results).

So I made a simpel web-based converter. It allows you to open a file to convert and apply some simple changes (invert color, stretch to fit canvas, etc). It’s also able to read back a previously generated byte array to display the image.

Feel free to link to the interactive page at Github pages or to clone the repository and host it yourself (it’s pure html+javascript so you can run it locally/offline in your browser as well).

Check it out here.