How does it render pixel data to the terminal?

I've stumbled over sixels [1], but movy seems to use something else that also enables color output and a higher resolution?

[1]: https://en.wikipedia.org/wiki/Sixel

EDIT:

> It renders frames as ANSI half block characters..

Seems like the resolution looks better than it actually is in the screenshots. It effectively seems to be 2 vertical Pixels per character.