filter changing per scanline, grayscale, 4 bit 
no filtering, colour, 8 bit 
no filtering, grayscale, 8 bit
filter 3, colour, 8 bit 
filter 3, grayscale, 8 bit
filter 2, colour, 8 bit 
filter 2, grayscale, 8 bit
filter 1, colour, 8 bit 
filter 1, grayscale, 8 bit
filter 0, colour, 8 bit 
filter 0, grayscale, 8 bit
