Dispelling the Myth of Hand Scanning Densitometers

Does the scanning speed of the spectrodensitometer affect the accuracy of its measurements?

A highly inaccurate supposition of some handheld scanning spectrodensitometers for the print industry today is the notion that if you vary the speed with which you manually move the instrument than the accuracy of the measurements will be compromised. In reality, handheld scanning spectrodensitometers offer the exact same accuracy as the high-end automated scanning systems and are often times the perfect solution for the pressroom. An ideal environment for the handheld scanning spectrodensitometer is one in which print formats do not exceed 40” as it can become quite challenging to manually scan across such a long surface.

The SpectroJet is one example of a handheld scanning spectrodensitometer that helps dispel this myth that is still true of some of the competitive instruments in the marketplace today. The reason why the speed in which you manually scan with the instrument does not negatively impact the accuracy of the results is because there is an encoder in the wheels of this device that automatically senses speed shifts. This optical encoder detects the pace and rate of the movements of the instrument while simultaneously coordinating the measurements based on specific speeds. Thus speed variations become completely irrelevant to the accuracy of the measurements thereby allowing the instrument to be manipulated manually and still produce highly accurate measurement results.

Incidentally, the myth holds true for other vendor manual scanning spectrodensitometers as they do not have the encoder for sensing speed variations. Without the ability to detect speed variations in a manual scanning spectrodensitometer, it is virtually impossible to produce accurate measurement results. For example, if you were to measure the same color bar several times the measurement results would vary widely because the human hand cannot maintain the exact same rate of speed while manually moving the instrument across the color bar multiple times.

Another common misconception about scanning spectrodensitometers is the number of measurements the instrument is taking per patch. Many printers are under the impression that scanning spectrodensitometers are taking 1 measurement per patch when in fact most are taking multiple measurements per patch and averaging them out for a final result. The benefit of multiple measurements per patch is the reduction in print anomalies and the ability of the instrument to literally average out the error. This is a crucial factor in evaluating instruments especially when comparing scanning spectrodensitometers to handheld spectrodensitometers. It is not uncommon to get slightly different measurement readings when comparing results from a handheld device to a scanning device because the scanning device is simply taking more sample measurements which in reality lead to a higher level of accuracy.

Lastly, a thorough understanding of how aperture size affects measurement accuracy is also warranted. Although many in the industry believe that scanning spectrodensitometers with smaller apertures are not as accurate as handheld instruments with larger apertures, this is simply not true. This is because the large sampling of measurement data overwhelmingly compensates for the size of the aperture thus providing a highly accurate measurement result.