NIST Launches New Short Course in Display Metrology
by Edward F. Kelley
When it comes to display metrology, the National Institute of Standards and Technology (NIST) frequently has been described as a watchdog for keeping measurements honest. Watchdogs protect valuables, and manufacturers of quality displays appreciate how NIST has helped secure good metrology for the display industry for the past 13 years through the Display Metrology Project and the Flat Panel Display Laboratory (FPDL). As display technologies continue to emerge with ever-increasing frequency, there has never been a more important time for NIST to be good at what it does, and we take great pride in our work.
The goals of our work are to provide accurate measurements of physical quantities and to develop unambiguous methods to measure those quantities. This provides a bedrock of good metrology upon which the display industry operates and thrives. In this highly competitive business, it is impossible for everyone to afford the investment in a display-measurements laboratory for researching measurement methods. NIST fills this gap by working on methods to quantify display performance that are as simple as possible, robust, reproducible, and address the immediate needs of the industry. The results are available to all.
Early on in NIST's involvement with displays, we found that many supposedly easy measurement methods were not so easy. Without realization, many measurement results were being corrupted by instrumentation veiling glare. NIST worked on developing laboratory methods to avoid such problems. Reflection characterization is also very important. Because of the diverse types of material used in the new flat-panel displays, the reflection properties were no longer easily characterized by the simple measurement methods used for CRTs. Much reflection-measurement thinking in the display industry is still CRT-oriented, and that needs to change. Thus, we continue to work with industry-standards organizations to identify robust measurement methods that permit an adequate characterization of display reflection. The effort is not directed at any single display technology, but methods are currently being shared with the industry that are useful in characterizing reflection for all display technologies and in all lighting environments.
It sounds simple enough, but it is not. In various NIST seminars and courses on the difficulties in making measurements of displays, we always hear the same comment, from laboratory technicians to managers alike: "I had no idea it was so difficult!" In many cases, too much is expected of the instrumentation. A person unaware of such limitations can make terrible measurements with the best equipment; those sensitive to such issues can make remarkable measurements with many types of instruments. For example, errors well in excess of 1000% can be made when attempting to measure the luminance of a small dark region on a bright screen using an expensive scientific-grade array camera, but the errors can be reduced to a few percent if the measurement is made while carefully and properly accounting for veiling glare. Good metrology requires careful consideration of all experimental factors to identify the appropriate measurement methods to accurately characterize an instrument.
There is no substitute for getting your hands on some equipment and actually seeing the effects of measurement problems on display characterization. To answer this, the NIST FPDL now offers a short course on display metrology at the NIST campus in Boulder, Colorado (see the NIST FPDL Web site, www.fpdl.nist.gov, for more information). The three-day course includes a day of lectures followed by two days of hands-on work illustrating some of the common measurement problems and concerns as well as gaining a familiarity with photometry and colorimetry. The main purpose of this short course is to assist the display industry, especially newcomers to display measurements.
In addition to the short course, the FPDL is offering several new services on a cost-reimbursable basis, including a program to standardize color and luminance measurements. In this program, a gamut-assessment standard (GAS) has been created that employs narrow-band interference filters, neutral-density filters, and broadband filters to check out the capabilities of instrumentation used for color measurements. The GAS is a portable instrument that can be sent to a customer to allow them to evaluate its display characterization methods. NIST experimentally confirms the GAS parameters before and after shipment with the measurement results being shared with the customer. With many display technologies exhibiting narrow-band spectra to create their color primaries, it can be too much to expect that a luminance meter or colorimeter will be able to handle these narrow-band spectral components properly. To be sure that such an instrument is capable of measuring any display technology accurately, the GAS offers a very large gamut based upon narrow-band sources over a large range of luminances. Tungsten-halogen white points are broadband sources that serve many calibration needs, but many of us worry if our meters can handle the saturated colors properly. If the GAS is found to be measured properly, these worries are eliminated. Such measurement assurance allows us to identify real achievements or real color problems in the objects being measured rather than contending with the uncertainty of whether or not a detected problem is with the measurement instrument or the measured object.
These programs exist to support the display industry. In general, the metrology efforts at NIST support many industries, and NIST needs to ensure that its resources are expended for maximum impact across our economy. The NIST FPDL continues to look for important and meaningful ways to support the entire display industry and enjoys hearing from industry representatives about their measurement needs and obstacles.