A statistical study of dirt-count measurement system variation using optical-scanner-based image analysis

Optically-based systems have been introduced to replace traditional visual methods for quantifying the amount of finely divided ink particles that show up as visible specks in pulp. There is no standard method for evaluating the accuracy and precision of these new systems, but the authors present a general method for the quantitative comparison of two ''dirt count'' measurement systems. The variation in the measurement system was reduced significantly using a Hewlett Packard ScanJet IIc as the scanning device in place of the earlier ScanJet Plus scanner when both were operated at 300 dpi. Variation was further reduced when the ScanJet IIc was operated at 400-dpi resolution. The ScanJet IIc also provided better accuracy.