In each, the image data is compressed in the same format, but the graphics are compressed differently. Therefore graphics compression TYPE B was developed. The uncompressed image files consist of two bytes per pixel. Bit 7 is most significant bit. Bit 0 is least significant bit.
Image compression is based on the difference between previous and next pixels.
The compressed image data is written as a string of 8-bit bytes, according to the following scheme. Pixel 1 is the first pixel of the image. There are no graphics data in any of the example pixels. That is, the graphics bits in these blank pixels are zero. TYPE A compresses the blank areas, or or zero graphics pixels.