Looking at the code and the actual file generated, it seems that the image is not compressed at all, using one byte per pixel. It also defines a palette of 128

Looking at the code and the actual file generated, it seems that the image is not compressed at all, using one byte per pixel. It also defines a palette of 128 colors, which is mostly unused. A bit of compression would drastically reduce the image size, this kind of monochrome images of axis-aligned blocks compress very well !