visibility measurement to test the effectiveness of a demister system

(en Français)

The purpose of demister is to recover the visibility through the windshield. Mist can happen almost instantly on a windshield if the conditions of humidity, pressure , and temperature are met. Mist may go with a transparent veil which lowers the contrast of the image in a translucent veil through which we no longer distinguish objects.

A demister system can implement very different technologies :

 - Air conditioning, blowing air on the windshield

 - The integrated windshield heating : it is used for a long time on the rear window , and it 's getting on the windshield , with the appearance of transparent conductors embedded in the glass.

The demister testing is traditionally performed "by hand " ( or " by eye" ) : an operator draws contours of the area he considers steamy on a layer placed on the windshield. He is equipped with a stopwatch, and the evolution of his drawing over time reflects the effectiveness of demister . This is a very basic method. In particular, it makes no distinction of transparency : it's either with steam or without steam.

The idea for testing a demister system in a more industrial way is to use a system for measuring visibility. The company NEXYAD has developed such a system (the tester VisiNex ) that was used in the study by the automotive supplier SAINT GOBAIN during the research program SURVIE , labeled by the competitive cluster Mov'eo, and co- funded by the French Government.

The visibility measurement performed by the tool VisiNex is predictive of human feeling and performance. This tool uses mathematical models of the human vision system that needs, in order to detect objects , a compromise between accuracy in luminance (number of gray levels between two levels of light  : for a digital camera, it would depend solely on the number of bits) , the available contrast , the size of the objects to be detected.

On the photographs below , we can see the shapes of clouds, although there is no contour and the contrast is low ( but the objects are large and the image is rich of gray levels) . Similarly, the stars are well detected in the black sky , although the objects are very small, there are only two values of gray levels (but the contrast is very high).

 
very low contrast (no contour and yet we                                 very high contrast (shapes bounded by an edge)
clearly see the shapes of the clouds).                                       Very poor image grayscale, and high contrast.
rich grayscale.

VisiNex estimates a distance of detection, on which can be computed the Johnson criteria to assess the distance of recognition and identification.
NEXYAD also developed a measure called Visual Quality Score ( VQS ) which measures the ease of detecting and recognizing (or read) objects.

Application to test demister :

One generates mist , then one starts the demister . A camera is installed in the vehicle , watching the VisiNex targetsoutside . VisiNex tool measures the change in visibility ( eg VQS ) during demisting :

Comparison of two demister systems : the initial visibility is the
same (same initial mist) and the final visibility is of course
the same ( no more mist )

Similarly, you can compute the visibility score on square areas (eg 5 cm x 5 cm) and make an animated mapping of misting over time.

For more information , contact NEXYAD Automotive & Transportation: http://www.nexyad.com/Automotive-Transportation

Presentation of the VisiNex testing system : http://nexyad.net/Automotive-Transportation/?page_id=159

Contact: sales@nexyad.com

Other applications: test wiper system