The cell modulation parameter is similar to the modulation parameter used in the ISO 15415 grading scheme; however, the process for computing cell modulation is different from the process used to compute modulation. Cell modulation is computed according to the following formula:

If (R < T2) then CM = (T2 - R)/(T2 - MD) otherwise CM = (R - T2)/(Mean Light Target - T2)

where R is the reflectance of the cell T2 is the threshold created using the historgram of the grid center MD is the mean of the dark lobe from the final grid-point histogram Mean Light Target is the mean of the light lobe from the final grid-point histogram The following list shows how codeword grading for modulation is calculated.

  • A (4.0) if modulation ≥ 0.50
  • B (3.0) if modulation ≥ 0.40
  • C (2.0) if modulation ≥ 0.30
  • D (1.0) if modulation ≥ 0.20
  • F (0.0) if modulation < 0.20

The following figure shows a Data Matrix code with a cell modulation grade of D.