visibility measurement and Johnson criteria

(version française ICI)

Visibility measurement can be accomplished in several ways:

 - Very basic methods measure the attenuation of a light beam as a function of distance, in transmission ( through the mist , for example) or in reflection ( to test the effectiveness of the markings on the roads to improve visibility) .
 - Heuristic approaches that measure the contrast of images and calibrate heuristically in terms of visibility

But there is a much more rigorous approach (both general about the possible causes of reduced visibility , and totally correlated to human perception ) : the Johnson criteria .

The approach is to compare the available contrast on each angular frequency , with the contrast that is necessary for human perception to detect, recognize and identify objects .

It is therefore a human factor driven approach , and not an approach of physicist working on the transmission of a light signal.

This approach is implemented in a commercial tool ( VisiNex ) developed by the French company NEXYAD .
It is therefore possible to make accurate measurements , repeatable and 100% correlated with human perception :
 - in Laboratory : with VisiNex tool
 - In the real world with an embedded version of VisiNex : Onboard VisiNex

For more information : http://www.nexyad.com and click activities NEXYAD Testing and NEXYAD Automotive & Transportation

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