Optimization of contrast, reflectance and sparkle of display systems with scattering anti-glare layers
Portable and hand-held electronic devices for entertainment and professional applications (smart phones, tablet computers, etc.) with touch-sensitive input are becoming ubiquitous these days. The visibility of the displayed information in bright surrounds however (outdoors with daylight as well as indoors with electrical illumination) is often poor and needs improvement. Optimization of the visual performance of such devices requires some engineering expertise as well as suitable metrology approaches in order to achieve the required degree of usability of the products.
Why do our "smart" electronic helpers present their magic in form of colorful, well saturated images with high contrast only in dark or dim surrounds with those features collapsing to invisibility in the presence of bright ambient light sourcesand high levels of illuminance?
Which are the physical effects leading to such impressive degradations and how can they possibly be avoided? This report tries to answer the raised questions and to provide some insight in the underlying mechanisms.
1 Contrast of Display Devices
The visibility or rather the readability of visual information like alpha-numeric characters, text and symbols presented on electronic visual displays is primarily given by the contrast.
CIE ILV 17-251 "contrast:
1. in the perceptual sense: assessment of the difference in appearance of 2 or more parts of a field seen simultaneously or successively (hence: brightness contrast, lightness contrast, colour contrast, simultaneous contrast, successive contrast, etc.);
2. in the physical sense: quantity intended to correlate with the perceived brightness contrast, usually defined by one of a number of formulae which involve the luminances of the stimuli considered: for example by the proportional variation in contrast near the luminance threshold, or by the ratio of luminances for much higher luminances").
Summary and conclusion
In order to ensure the recognizability of visual information displayed on electronic screens even in bright environments, contrast must be maintained, which is only possible by controlling reflections. Touch-screens mounted in front of the display increase the amount of reflected light, which can only be kept within acceptable ranges by carefully designed optical coupling. A matte first surface can suppress reflections and avoid mirror images, which leads to good ergonomic performance, but only if the amount of sparkle is kept witin acceptable limits at the same time.
Additionally, scattering anti-glare layers for control of reflections may reduce the "distinctness of image" of the intended visual information as presented by the display screen (blurring of details). This reduction must as well be limited and thus it must be measured for optimization of the visual performance of the complete display system.
The SMS-1000 provides four essential measurements for optimization of visual display performance:
1 measurement of sparkle,
2 measurement of "distinctness of image" (DOI) with the pixel matrix of your display,
3 measurement of the transmittance distribution function (TDF) from which metrics can be obtained to specifiy image blurring,
4 measurement of the reflectance distribution function (RDF) from which metrics can be obtained to specifiy the degree of reflection control.
SMS-1000, THE solution for comprehensive optimization of visual display performance in the presence of scattering anti-glare layers.
SMS-1000 Features and Specifications
Literature References
[1] Michael E. Becker: Matte vs. glossy displays – a technical discussion, Electronic Displays Conference 2010
[2] en.wikipedia.org/wiki/Anti-reflection_coating
[3] Michael E. Becker, Jürgen Neumeier: Measurement and characterization of the sparkling of AG coated LCDs,
Electronic Displays Conference 2011
[4] Michael E. Becker: Measurement and evaluation of display scattering, JSID 13,1(2005), p. 81-89
