Introducing the International Committee for Display Metrology (ICDM)

The International Committee for Display Metrology (ICDM), the first standards-development committee within SID, is preparing a metrology standard for practical and relevant measure-ment methods for the complete evaluation of displays. This will provide display manufacturers, equipment makers, those who commercialize displays, and any level of user a common language to ensure that all display measurements are performed in the same manner, and correctly. This article details the efforts and goals of the ICDM.

by Joe Miseli

THE DISPLAY INDUSTRY has reached a tremendous state of technology development today. Products which are currently produced and will be forthcoming are often breath-taking. Displays of immense proportions have been built having excellent performance, and they keep getting bigger, better, and lower in cost. They have advanced much further than all but the most gifted visionaries might have imagined a scant 20 years ago, when the market was completely dominated by cathode-ray-tube (CRT) displays with sizes rarely exceeding 30 in. Just two decades later, wall-mountable flatpanel displays over 50 in. are quite common and low in cost, with sizes increasing so much that some are too big to be hung on the walls of many living rooms!

Along with great-looking displays and evolutionary technologies comes an increased need to analyze their characteristics so that those who use, build, specify, and qualify displays can understand their true performance quality. This can be complicated because some display-performance characteristics are stated with figures in a less than clear and precise manner or creatively expressed to favorably skew the perception of performance. We can avoid this "specsmanship" by use of solid metrology that uses well-defined terms and definitions, clear and precise measurement and evaluation procedures, etc. By doing so, we will help reduce or eliminate the proliferation of these items. This is where evaluation by metrology standards comes into play.

Fig. 1: Shown is the ICDM logo.

The best of the display-evaluation standards is considered to be the VESA FPDM2 (Flat Panel Display Measurement).¹ It is held as the definitive reference, and many other display standards leverage off it. However, it was last updated in 2001, and further work was halted when the FPDM activity at VESA was dissolved. Because display products are evolving at an amazing pace, the standards MUST keep pace.

The International Committee for Display Metrology (ICDM), part of the Definitions and Standards Committee of SID, has undertaken this task (Fig. 1). A new display-metrology standard (DMS) for the measurement and evaluation of displays is forthcoming from the ICDM, which includes the core group of individuals who wrote the FPDM with expanded participation of world experts from within the SID membership in the area of display evaluation. SID is the foremost display association in the world and consists of most of the display professionals in the industry, either as active members or associated with member companies. Experts of the Committee Working Group include display engineers, metrologists, color scientists, vision scientists, university researchers, human-factor specialists and ergonomists, as well as others with additional specialized display-related skills.

Philosophy and Goals

One of the goals of making the ICDM a universally accepted display-measurement standard is collaboration with other standards bodies, not competition with them. We want to take the burden of defining the full set of measurement methods off them so that they can reference the ICDM DMS and concentrate on other aspects, such as specifications, recommended practices, etc. As a result of these these efforts, the other standards bodies can produce standards to help rate the actual performance of a display for various parameters and to state what is good or bad based upon ergonomic considerations or other science. The ICDM standard provides the tools and methods to determine the performance numbers, while the other standards provide guidelines on what is good or bad, acceptable or not, or is expected.

The first version of the ICDM DMS will be available in 2008 (Fig.2). The ICDM plans for it to be available as a free download from the SID ICDM Web site (http://www.icdm-sid.org). We invite those who perform the measurements or actively use the standard in other ways to participate by way of feedback on the Web site. The ICDM also plans to make available a printed version for a nominal cost, with value-added content for the purchaser. This includes a bound copy of the standard along with a DVD-ROM containing many extras, such as test patterns for multiple resolutions, supplemental documents, and perhaps software templates. The ICDM will provide test patterns to make measurements when using the standard. These will be downloadable from the Web site and will also be included on the DVD-ROM.

ICDM DMS Style

The ICDM proposes a series of goals and parameters for writing the DMS. In the following sections, the italicized text details those goals which are followed by additional explanations for each of them where necessary.

• The ICDM DMS is designed for all display configurations and technologies, from bare panels to finished monitors, TVs, and signage displays, and from liquid-crystal displays (LCDs) to plasma displays to organic light-emitting-diode (OLED) displays, as well as flexible, reflective, portable, and projection displays, 3-D, electronic paper, etc.

The standard is display-technology independent wherever possible. Parameters such as luminance, uniformity, contrast, color saturation, and reflection tend to be common to all displays; their measurement methods should also be common. Other metrics such as viewing-angle characterization, luminance loading, geometric distortion, inter-image differential parameters (as is found in 3-D displays), and differential aging are more display-technology dependent. The ICDM DMS works to combine the similarities and account for the variabilities.

• Keep the style, language, and methods simple and short, using plain English and abundant graphics. Cartoons are added to give the document a friendly manner.

The ICDM DMS is written in plain English with no slang, jargon, idioms, technospeak, or colloquialisms. We maintain a style that is basic and consistent. Detailed terminology, definitions, and technical discussions are separated into other sections of the document to avoid complicating the measurements pages. In addition, many graphics and icons are used to help avoid misinterpretations by non-native English-speaking users.

• To have a common terminology so that everyone can use the same terms and understand the same meanings regarding display metrics.

It can be found today that different terms are sometimes used for the same measurement, and use of improper terms for display metrology is not uncommon. These can cause confusion and misinterpretation of measurement results as well as problems in communicating them. For example, the term residual image may also be known as image sticking, image retention, latent image, or burn-in, although some of these terms, such as burn-in, have entirely different meanings. The standard uses terms precisely.

• A single measurement is presented on a single page wherever possible, keeping the number of words to a minimum, providing common structure, consistent style. There are icons that represent test conditions (especially for repetitive tasks). Extensive details, references, and technical discussions are included in separate sections of the document specifically dedicated for those purposes with hyperlinks to easily access them.

Some display-metrology-measurement or related standards concentrate on one or only a few test items within a given document. There may be many pages written to describe a single measurement method. This can make the test unclear, confusing, and sometimes unmeasurable. The ICDM DMS document is comprised of many parts, and we strive to limit each test to one page in length, although there are a few tests that extend to two or more pages. We use icons to simplify repetitive tasks and reduce extra wording (Fig. 3).

Figure 3 illustrates some of the ICDM Measurement Section icons (from left to right: "Ambient Illumination Conditions," "Controls Unchanged," "Imaging Light Measurement Device (LMD) Field of View and Subtense Angle," and "Electrical Conditions").

Document Structure

• No numbers that represent values or expected results are used in the standard – only methods and supported examples. The ICDM standard does not state how good a display is or what is expected, only how to measure it.

We do not state what constitutes good image quality in terms of acceptability or preference – we state what is good metrology. Nor do we state or suggest how to rate a display. Rather, we describe the methods to measure them so that the results produce valid numbers that accurately state a display's performance.

Supported examples describe how to make the measurements – these examples represent methods, not results or expectations of a display's performance or capability.

• The ICDM DMS describes how to make measurements on a display, or methods for Display Metrology. Display measurements are based on photometry and colorimetry, which by their nature are both vision/ergonomic measurements. Of the unlimited number of measurements that can be performed on displays, it may be advantageous to choose only those which are meaningful in terms of human vision.

The participants of the ICDM include display-evaluation specialists with many areas of expertise including psychophysics, human vision, and ergonomics, all of whom can help determine relevance, usability, and presentation. They help complement proper metrology by validating the methods and assessing the relevance.

For example, let us examine the perception of motion. Motion does not exist on a display; rather, a "moving" object changes its location or position on the display every refresh period; i.e., it is a jump in position, not a continuous smooth motion. The eye performs a psychophysical transformation to convert that jump stimulus into a perception of motion by means of smooth-eye pursuit and intrinsic psychophysical filtering.

Some measurements might be qualified in terms of human-visual characteristics; e.g., we can measure flicker beyond the human-vision perceptibility limits, and we may need some determination to help analyze what is meaningful. Relevancy of human-visual perceptions vs. instrumental capabilities has important interactions that must be weighed.

• Many times, display-performance issues are easy to recognize but very difficult to measure.

In such instances, these characteristics may be seen and their relative severity easily understood, but they might be very difficult to measure and determine their severity. Examples might be mura, residual image (also called image sticking), some motion artifacts, certain types of pixel defects, synchronization effects, improper colors, color matching, dynamic-range compression, and temporal distortions. The ICDM DMS addresses these types of items and provides information to help assess them, including setup conditions and some guidance for expectations.

• Putting measurement results together in a coherent and meaningful manner can produce sets of composite metrics that can be used to define display-performance guidelines for predetermined environments or applications.

This can prove to be a valuable aspect of the ICDM standard, providing a method to perform assessment in a comprehensive manner. We put the pieces (or collections of metrics) together into sets in order to obtain extremely valuable and relevant composite metrics. Such measurements could be creatively combined to determine metrics for a display to be used for a monitor, a TV, a theater, a broadcast reference monitor, a living room, outdoors, an office, an operating room, or a radiology environment.

Committee Organization and Participation

The ICDM membership includes some of the world's foremost experts in a number of fields that help characterize display performance and quality. Examples of these fields include display metrology, color science, psycho-physics, vision science, human factors, display engineering, display design, testing and test-equipment manufacturing, display manufacturing, and component manufacturing. In addition, ICDM development applies the skills of conventional science and engineering, such as physics, optics, electrical engineering, chemistry, and mechanical engineering.

The officers of the ICDM were elected on May 23, 2007 at the SID Display Week 2007 ICDM meeting in Long Beach, California, USA.

• Chair: Joe Miseli (Sun Microsystems)

• Editor-in-Chief: Ed Kelley (NIST)

• Vice Chair for Asia: Jongseo Lee (Samsung)

• Vice Chair for Europe: Michael Becker (Display-Metrology & Systems)

• Vice Chair for Human Factors and Vision Science: Andrew Watson (NASA).

ICDM Web Site

• A place where members have access to ICDM display-standard- development-related documents and communication tools, and the world can have access to the ICDM.

The ICDM Web site (http://www.icdm-sid. org) is designed for open access to the ICDM and its work, and for ICDM participants to have a members-only home reference location for document exchange and communications tools to help develop the ICDM display-measurement standard. This site is the home to ICDM activities (such as round-robin testing), links to other appropriate pages, and a depository for ICDM downloads.

One goal of the Web page is to include references to help users to better utilize the ICDM, including data of worked-out examples per the ICDM standard. One consideration is ICDM certification or validation when using the standard. Concepts are yet to be determined for this ambitious goal.

In addition, there are two Wiki sites for the ICDM. One is on the SID Wiki site and the other is on Wikipedia:

• ICDM SID Wiki page URL: http://wiki. sidmembers.org/ and search for ICDM.

• ICDM Wikipedia page URL: http://en. wikipedia.org/wiki/ICDM.

The Wikipedia site leverages the vast amounts of information posted on Wikipedia related to display performance and parameters. The SID Wiki site provides a format for links to complementary pages established and primarily authored by ICDM participants.

Characteristics, Activities, and Summary

There are many goals and plans for the ICDM beyond what can be referenced in one article. Here are just a few:

• Address common measurements, and assure that they are standardized and well understood.

• Address difficult and future metrology needs which have not yet been standardized.

• Have separate sections for measurements, metrology, technical references, discussions, glossary, definitions, etc.

• Write the DMS in stages. The first version will have reduced content. Subsequent versions will address more advanced and/or difficult measurements, such as motion artifacts beyond motion blur.

• Establish standard setup and testing conditions to assure accuracy in testing and work to eliminate "wiggle room" so that all who test displays cannot manipulate setup conditions to give them preferential results of their measurements.

• Establish a palette or buffet of measurements so that the user can choose the desired test, thus providing different ways to make a measurement within the same category.

Acknowledgments

The ICDM Committee Working Group members, from whose discussions, key points, ideas, and words helped formulate many parts of this article, are greatly acknowledged for their efforts. Special thanks to Ed Kelley for his invaluable contributions to the formation of the structure of this article.

References

¹P. Downen, "A Closer Look at Flat Panel-Display Measurement Standards and Trends," Information Display, 16-21 (January, 2006). •