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Overview: Many of the problems in making good display measurements are related to how well or how poorly we deal with stray light or scattered light. People sometime choose to ignore the effects of such scattered light with serious consequences to the reproducibility of their measurements. Often the assumption is made that stray light is not important and too much is expected from the instrumentation. In light detection equipment, veiling glare and lens flare can introduce large errors whenever anything but the simplest objects or patterns are measured. Methods are presented to diagnose and correct for stray light effects in making measurements on displays. Abbreviations: SLET (stray-light-elimination tube) Publications: NIST Stray Light Elimination Tube Prototype: (SLET_04.pdf) -- This paper (also found on the Projection page) describes the creation and use of the first SLET, how to make a portable darkroom using a SLET, and the use of a slit illuminance meter with a SLET. Citation: P. A. Boynton and E. F. Kelley, "NIST Stray Light Elimination Tube Prototype," NISTIR 6861, March 2002. Measurements of Static Noise in Display Images: (SPIE01-StaticNoiseCCD-Meas.pdf) --This publication (also found on the Detectors page) describes the difficulty of making accurate luminance measurements of small areas on complicated images. Measurements made on a noise pattern using a narrow-frustum SLET (stray-light-elimination tube) is compared to a typical array imaging device using a lens. The errors can be alarming if we are not careful. This material is not to dicourage the use of such array detectors. Rather, it is intended to make people aware of their possible limitations and offer diagnostics to determine any possible limitations. Citation: J. W. Roberts and E. F. Kelley, "Measurements of Static Noise in Display Images," Proceedings of the SPIE V4295B-27, Electronic Imaging Symposium, San Jose, CA, January 23, 2001. Small-Area Black Luminance Measurements on a White Screen Using Replica Masks: (SmallArea1.pdf) --Small area measurements of dark regions with bright backgrounds are subject to significant errors from veiling-glare corruption of the dark regions. A method is described using a replica mask and a diagnostic is presented to assure the measurement accuracy. Citation: P. A. Boynton and E. F. Kelley, "Small-Area Black Luminance Measurements on a White Screen Using Replica Masks," 1998-SID International Symposium Digest of Technical Papers, Society for Information Display, Vol. 29, pp. 941-944, Anaheim, CA, May 17-22, 1998. Accurate Contrast-Ratio Measurements Using a Cone Mask: (ConeConSID97.PDF) --Veiling-glare corruption in the detector can be significantly reduced with the use of a gloss-black frustum (cone with tip cut off). Comparisons are made using a frustum and a flat mask. Citation: P. A. Boynton and E. F. Kelley, "Accurate Contrast-Ratio Measurements Using a Cone Mask," 1997 Society for Information Display (SID) Symposium, Digest of Technical Papers, May 11-16, 1997, Boston, MA, Sec 32.1, pp. 823-826 (May 1997). Light-Measuring-Device Checking Targets: (LMDchk01.ppt) --Set of images used to examine the characteristics of the detector used to make detailed luminance measurements in complicated images. "LMD" means light-measuring device. Frustum Calculation Spreadsheet: (Frustum.xls) -- A simple spreadsheet that calculates the cuts needed in a flat sheet of black gloss plastic to make a frustum of a certain apex angle. Notes: 1. See any stray-light-elimination tube (SLET) discussions in Projection Metrology. 2. In SED Camera (simulated-eye-design camera) we attempt to reduce such veiling glare in the detector. 3. Also see the lasest seminars or courses here . Updated 20111009T0745 |