Epson SQ-2550 User Manual page 132

Write the assigned values of the nozzles next to your design
and then total the values for each column of dots. These totals
are the values that will be sent to the printer as graphics data to
print the design.
Below is shown the same grid divided into three sections to
make the data calculation easier. At the bottom of each section
of each column is the total of the nozzle numbers for that
section. This gives you a total of 126 data numbers necessary to
print this small figure.
Software and Graphics 4-17
Graphics