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Sunday, August 4, 2013

Density vs. Reflectance Measurement (Part 2)

In a continuation from the previous article, other differences between reflection densitometers and reflectometers are as follows:

2) Spectral response - most colorimeters closely match the spectral response of the standard human observer. Densitometers do not.  Densitometers are not intended to see color in the same way that is viewed by the human observer, but rather they are intended to relate to the tinting strength of individual inks relative to a control ink strength.

3) Area of measurement - densitometers measure small areas, typically 1-6 mm diameter. Most reflectometers measure larger areas typically 6-50 mm diameter.

4) Shade discrimination - good quality reflectometers have the ability to discriminate between shade differences better than the human eye throughout the entire reflectance range of 0 - 100%.  Typical densitometers, with their logarithmic scale, do not become equivalent to the human eye in its ability to discriminate shade differences unless the shade has a reflectance of less than 30% (density = 0.5).  The densitometer has better shade discrimination capability for very dark shades with reflectance of less than 5%.

When the densitometer is used for its originally intended purpose of determining the amount or strength of individual colorants, it does an excellent job.  The densitometer user should resist the temptation to use it as a general purpose brightness, opacity or color tester as it is unsuitable for these measurements.

If you have other questions on the topic contact me at toddp@technidyne.com.