We report on the characterization of two novel probes for measuring display color without contamination from
other screen areas or off-normal emissions. The probes are characterized with a scanning slit method and a
moving laser and LED arrangement. The tails of the scans indicate the spread in signal due to light from
areas outside the intended measuring spot. A dual-laser setup suggests that color purity of the reading can be
maintained up to a few tens of millimeters outside of the measurement spot, and a dual-LED setup shows the
effects of secondary light emissions in the readings. The first design, color probe A, is then used to quantify
display color, maximum color difference, luminance uniformity, graylevel tracking, and angular color shifts of
medical liquid crystal displays and mobile displays.
The accurate measurement of spatial resolution can be critical in the characterizations of projection display systems. Techniques can be used to determine resolution of projection systems by measuring the contrast of alternating grille patterns or fully modulated sine waves of various spatial frequencies. Unfortunately, the measurement of the contrast of these patterns may be influenced by stray light, either from ambient and reflected light in the environment, or from veiling glare (light scattering) in the lens of the light-measuring device. Such stray-light corruption can lead to large errors in contrast determination, providing an inaccurate and misleading characterization of the projector. For large-area measurements, various tools and methodologies have been employed, including the use of frustums and masks, to minimize such unwanted effects and provide a more accurate measurement. With some modifications, these same tools may be used for small-area measurements with similar results. Results will be shown comparing resolution determinations using different test methodologies with and without stray light compensation.
With the advent of digital cinema, medical imaging, and other applications, the need to properly characterize projection display systems has become increasingly more crucial. Several standards organizations have developed or are presently developing measurement procedures (including ANSI, IEC, ISO, VESA, and SMPTE). The National Institute of Standards and Technology (NIST) has played an important role by evaluating standards and procedures, developing diagnostics, and providing technical and editorial input, especially where unbiased technical expertise is needed to establish credibility and to investigate measurement problems.
Light-measurement instrumentation based upon high-quality charge-coupled-devices (CCD) is currently in use for measuring the characteristics of electronic displays. When such array detectors are used to measure scenes or images having high contrasts or wide color variations, they can suffer from the effects of veiling glare or lens flare and thereby inaccurately measure the darker luminances because of a mixing of the scene luminances or colors. A liquid-filled simulated-eye design (SED) camera was constructed to improve the ability to measure such images by reducing the internal scattering that contributes to the veiling glare. This paper discusses the investigation of the use of various liquids, in particular the effects of scattering within the liquids.
The NIST Flat Panel Display Laboratory (FPDL) is operated through the Display Metrology Project (DMP) of the Electronic Information Technology Group in the Electricity Division of the Electronics and Electrical Engineering Laboratory of NIST. The DMP works to develop and refine measurement procedures in support of ongoing electronic display metrology, and applies the results in the development of national and international standards for flat panel display characterization.
In earlier papers, NIST proposed a standard illumination source and optical filter targets with which to assess the state-of-the-art of display measurement. The Display Measurement Assessment Transfer Standard (DMATS) was designed to present the display metrologist with a rectangular array of targets such as color filters, polarizers, and grilles, back-lighted by uniform illumination, to be measured using methods and instruments typically used in display performance measurement. A “round robin” interlaboratory measurement exercise using the “standard” artifact suite would enable a first order assessment of display measurement reproducibility, i.e., measurement variability within the electronic display community. The rectangular array design of the DMATS was anticipated to present stray light and color contamination challenges to facilitate identification of error sources deriving from measurement protocols, laboratory environment, and equipment. However, complications in dealing with heating problems threatened to delay the planned laboratory intercomparison. The Gamut Assessment Standard (GAS) was thus designed as an interim solution to enable the NIST scientists and participating measurement laboratories to begin collecting data. The GAS consists of a 150 mm diameter integrating sphere standard illumination source with a stray light elimination tube (SLET) mounted at the exit port. A dual six-position filter wheel is mounted at the SLET exit port. One wheel holds a series of neutral density filters and a second interchangeable wheel holds various color filters. This paper describes the design and construction of the GAS, its initial performance characterization by NIST, and comparison measurements made at NPL. Possible design changes suggested by the results of the preliminary intercomparison are discussed, as are plans for future interlaboratory comparisons and potential use of the GAS as a transfer standard for laboratory self-certification.
The accurate measurement of small area-black levels is important in projection display characterization. For example, techniques can be used to determine resolution of projection systems by measuring the contrast of alternating grille patterns or fully-modulated sine waves of various spatial frequencies. Unfortunately, the measurement of the contrast of these patterns may be influenced by stray light, either from ambient and reflected light in the environment, or from veiling glare scatter in the lens of the light-measuring device. Such stray-light corruption can lead to large errors in contrast determination, providing an inaccurate characterization of the projector. For large-area measurements, various techniques have been employed, including the use of frustums and masks, to minimize such unwanted effects and provide a more accurate measurement. With some modifications, these same tools may be used for small-area measurements with similar results. The design, construction, and implementation of these tools will be discussed. Results will be shown comparing small-area contrast measurements of projection systems, including resolution determination, with and without stray light compensation, for different measurement instrumentation.
Most would assume that the characterization of electronic display quality would be a straightforward process offering few complications. However, what the eye sees can be very difficult to capture accurately and quickly in a meaningful way. With the advent of many new display technologies, there is a need to a level playing field so that different technologies can be compared on an equivalent basis. Orchestrating display metrology to accomplish this is wrought with several difficulties that will be reviewed especially in the areas of stray light management/measurement and meaningful reflection characterization.
Flying-spot displays use narrow-spectrum high-power sources that scan the image across the display screen. They can provide a bright display with a large color gamut. When such displays are measure with conventional light-measuring devices (LMDs) such as luminance or illuminance meters, there is concern that the LMD may not accurately measure the display's photometric and colorimetric output. The unique characteristics of the source may exceed the limitations of the instrumentation. A series of diagnostics has been developed that allows for an evaluation of LMDs for use in measuring flying-spot displays. Limitations resulting from LMD saturation, timing, and tristimulus or photopic filters can be revealed, and in some cases, specific causes can be identified. Each diagnostic will be demonstrated using several instruments, including luminance meters, illuminance meters, colorimeters and spectro radiometers. Using a simple comparison box, flying-spot displays can be viewed side-by- side with steady-state sources in a bipartite image. After the sources have been visually matched in color and luminance, the two images can be measured with a particular LMD, and results compared. Any significant difference between results would indicate a limitation of the LMD. Further diagnostics, using integrating spheres, neutral density filters and interference filters, are used to aid in identifying the nature of the limitation, and in some cases, point to solutions.
A prototype display measurement assessment transfer standard (DMATS) is being developed by the NIST to assist the display industry in standardizing measurement methods used to quantify and specify the performance of electronic display. Designed as an idealized electronic display, the DMATS illumination source emulates photometric and colorimetric measurement problems commonly encountered in measuring electronic displays. NIST will calibrate DMATS units and distribute them to participating laboratories for measurement. Analysis of initial interlaboratory comparison results will provide a baseline assessment of display measurement uncertainties. Also, diagnostic indicators expected to emerge from the data will be used to assist laboratories in correcting deficiencies or in identifying metrology problem areas for further research, such as measurement techniques tailored to new display technologies. This paper describes the design and construction of a prototype DMATS source and preliminary photometric and colorimetric characterization. Also, this paper compares measurements obtained by several instruments under constant environmental conditions and examines the effects of veiling glare on chromaticity measurements.
The appearance of noise on a display is an important usability issue. Sources of noise include electrical interference, display driver artifacts, resampling artifacts, transmission artifacts, compression artifacts, and any intrinsic noise artifacts produced within a display device. Issues for the severity of the noise problem include total magnitude of noise, noise spatial frequencies, proximity of the noise spatial frequencies of the desired information content and the human-eye response to that information content, uniformity of the distribution of noise, and appearance of any visible or regular patterns in the noise. Whatever the source, an accurate method to measure noise may be required to properly assess the influence of the noise. We investigate the intricacies of using a digital camera to accurately measure noise in a static image on a flat panel display (FPD). The electro- optical transfer function of the FPD is measured. A known noise pattern is displayed and measured using the digital camera whereby the predicted noise is compared to the measured noise. Complications and limitations in the metrology will be discussed.
Flying-spot displays scan an image across the display screen using a high-energy beam. Each pixel can be a narrow, submicrosecond pulse. When such displays are measured with conventional light-measuring devices (LMDs), such as luminance or illuminance meters, there is concern that the LMD may not accurately measure the display light output because of the unique characteristics of the source. The LMD may be unable to properly integrate the narrow pulses, or the high-energy signal may saturate the detector. As in all areas of metrology, it is essential to verify that the instruments used are providing the desired information. A diagnostic has been developed that allows for an evaluation of LMDs for use in measuring flying-spot and similar displays. This method tests for both integration and saturation errors using a bipartite comparator and a neutral density filter. Errors resulting from the saturation of the LMD by the flying-spot display are demonstrated. The construction and procedure of the diagnostic is described. Limitations of the technique as well as sources of error are presented.
Electronic front-projection display specifications are often based on measurements made in ideal darkroom conditions. However, not everyone has access to such a facility. In many environments, ambient light from other sources in the room illuminates the screen. This includes room lights directly illuminating the screen and the reflection of these light sources off of walls, floors, furniture, and other objects. Additionally, back-reflections from the projection screen must be considered. These stray light components contribute to the measured value, giving an inaccurate measurement of the projector light output. Thus, these conditions may make the task of adequately comparing and evaluating different projection systems difficult. We can better verify whether the projector is operating according to its specifications or compare its performance with other projectors by compensating for stray light. A simple projection mask constructed from black plastic and a stray-light elimination tube are presented as solutions that can provide an accurate measurement of projector light output in many ambient light conditions.
Light-measurement instrumentation based upon high-quality charge-coupled-devices is currently in use for measuring the characteristics of electronic displays. When such array detectors are used to measure scenes having high contrast or wide color variations, they can suffer from the effects of veiling glare or lens flare and thereby inaccurately measure the darker luminances because of a mixing of the scene luminances or colors. The simulated-dye-design camera attempts to reduce the effects of unwanted light contamination by copying some of the characteristics of the eye. This first prototype shows an improvement of a factor of 2.7 in its ability to measure high contrasts over a similar camera that is not filled with liquid.
The National Institute of Standards and Technology (NIST) has initiated a new program on performance measurements for flat panel displays. Prior to this progress, NIST completed an assessment of industry needs for measurements and standards to assist in the development of high-resolution displays. As a result of this study, a new laboratory has been established to characterize the electrical and optical performance of flat panel displays. The services of the laboratory will be available to commercial panel manufacturers and users. NIST, as a neutral third party, intends to provide technical assistance in the development of standards and measurement practices for flat panel display characterization.