I needed more colour 
So have now added 31 and 255 colour support to my sprite class. I have also added a Windows executable which will take a bitmap and generate all the source code data automatically for pasting into your programs. Just make sure your bitmap is already colour reduced before converting.
https://github.com/AaronLiddiment/LEDSprites
I had a quick look at your repo and it looks good I will play around with it. A few years back I made a an LCD clock with an AVR. The display was 128x64 and was running out of space for my sprites/fonts… My solution was to compress the data. Ive tried different schemes RLE, Huffman… and also http://spin.atomicobject.com/2013/03/14/heatshrink-embedded-data-compression/ … Depending on the data I would get on aveage 25 to 50 percent reduction… It would be a great feature for your library.
Thanks. I did consider compression but when I originally wrote the class I was just looking at small game type sprites. I therefore made it colour table based and bit packed the colour index data using custom defines that made source code sprite design easy.
Now I have added the 8 bit mode and finally knocked up the source data generator I may look again.
I am currently playing with a 144x24 matrix on a Teensy, scrolling around 31 & 255 colour images several times larger than the matrix. Even though I have at least 13 images in the code, it is still less than 150K program and 18K ram.