Just how black is the black in that flat-panel display?
Until recently, manufacturers and users of high-contrast electronic displays, such as those used in laptop computers, were not sure. Using conventional measurement techniques, manufacturers could not assess accurately contrast ratio nor could they recognize when their measurements were in error. Results often varied, fueling complaints and making comparisons between brands or different technologies difficult. In addition, the ratio of the luminance of a white area to a black area on a display is a performance parameter that strongly influences the perceived quality of a display.
Now, two researchers at the Commerce Department's National Institute of Standards and Technology have devised a measurement technique that offers both manufacturers and industrial customers a means for accurately measuring the contrast ratios of displays in laptops, airplane cockpits, home entertainment centers and other applications.
Researcher Edward Kelley determined that the accuracy problem stemmed from unavoidable reflections in the lens of the measuring instrument. The reflections, also called veiling glare, were being introduced by illumination from the nearby lighter areas on the display surface.
The NIST method designed to eliminate the problem uses an open-ended cone to reduce substantially the reflections introduced into the lens system without interfering with the measurements. The cone can be positioned to reduce the glare to an insignificant amount.
Working with Paul Boynton, Kelley measured a display using conventional techniques and the newly developed NIST method. The former resulted in a value of 50 to 1; the latter revealed a more accurate contrast ratio of 250 to 1.
Boynton says, "We're using this work to help people understand the importance of developing a firm measurement base in the display industry. We want them to think more critically about how to make measurements."
According to Kelley, chair of the Video Electronics Standards Association flat-panel display measurement standards committee, VESA members will vote later this year to adopt a new flat-panel display measurement standard that includes the NIST-developed technique.
For technical information, contact either Edward Kelley, A53 Technology Building, NIST, Gaithersburg, Md. 20899-0001, (301) 975-3842, e-mail: edward.kelley [at] nist.gov or Paul Boynton at the same address, (301) 975-3014, e-mail: paul.boynton [at] nist.gov.
A non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.