before there was emailed with something called faxes where you could send documents over a phone line and the way it was encoded was by Senshi he's sending he naively would be uttered is fix less wide or block and as you step through the entire page naively you have to send one bit per pixel white or black very expensive because usually actually it's going to be a lot of light in a row or a lot of blacks in a row so you can instead encode it as the number of whites then the number of blocks number of lights it's called a thin coating and