to Delivering High Quality Images in Medical Monitors. Welcome!. Your Instructor & Sencore contact. Scott Reardon. 1-800-SENCORE www.sencore.com. About Sencore. Founded 1951 Located in Sioux Falls, SD
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to Delivering High Quality Images in Medical Monitors Welcome!
Your Instructor & Sencore contact Scott Reardon 1-800-SENCORE www.sencore.com
About Sencore • Founded 1951 • Located in Sioux Falls, SD • Leading manufacturer of innovative electronic test & measurement equipment: • Computer Monitor - high resolution computer monitor repair and calibration • Digital Video - MPEG-2/ATSC, MPEG-2/DVB, CCIR601 Serial/Parallel, QAM, and HDTV • High Definition TV - demonstration, testing and calibration applications • Professional A/V- high-end video display calibration and sound system analysis, & Home Theater • Medical - Safety Testers, Compliance Testers, and Analyzers, including SPO2 and Patient Simulators • Cable- RF distribution including CATV, MATV, satellite antenna systems & QAM applications • Broadcast- broadcast and studio settings, especially digital video and MPEG-2 applications
Introduction Medical Monitors Need Calibration! • Critical diagnoses depends on correct image display. • Incorrect white balance causes false color imaging. • Room lighting affects perceived color, brightness, and contrast. • Overdriven CRTs cause picture distortion. • Misadjusted User controls distort contrast and brightness ratios. • Small picture flaws are magnified on high resolution displays. • CRTs age - recheck calibration every 6 months
Introduction Why Perform Video Calibration? • Displays are aligned on location after installation and moving is completed • Picture is optimized for room lighting conditions • Reduce Doctor’s complaints about the display: • That it doesn't look right. • The red of the tissue doesn't look right. • The display is too dark or the display is too light. • The picture is blurry. • Assure the doctor that the image quality is correct • Produces full range of accurate colors & grayscale • Telemedicine - displays need to be calibrated to match what is happening on site
Video Review - Producing an Image Neg. bias 6.3v 400-800V Approx. 20-40% of HV 25KV CRT Operation • CRT gun (F1/F2, K, G1, G2) produces an electron beam • Electron beam is accelerated by high voltage • Phosphor screen gives off light when struck by electron beam
Video Review - Producing an Image How do video displays make B&W? • Changing bias (G1/K voltage) changes electron beam intensity • Higher bias = less beam current; less bias = more beam current • Less beam current = less light output; more beam current = more light output No light output Medium light output Maximum light output High bias Medium bias Low bias
Video Review - Producing an Image • White - all phosphor producing light • Black - no phosphor producing light • Contrast ratio - difference between black level and white level • Ambient light affects contrast ratio
Video Review - Producing an Image • Level of video signal corresponds to CRT gun conduction & brightness • Brightness (luminance) = average DC level • Contrast (difference between bright/dark portions) = peak-to-peak amplitude • Video signal levels specified in IRE
Video Review - Producing Color How do video displays make color? • Color CRTs use three electron guns • Each gun is fed a separate video signal (RGB) • Red + Green + Blue = white
Video Review - Producing Color No light output • Changing bias of all three guns equally produces shades of gray • Neutral gray is call White Balance • Good color tracking maintains “neutral” gray at all luminance levels High bias Medium light output Maximum light output Medium bias Low bias
Video Review - Signal Types Composite Video vs. S-Video (Y/C) • Composite video contains luminance, chrominance, and sync on the same signal line. • S-Video (Y/C) contains luminance and sync on one signal line, with chrominance on a second signal line.
Video Review - Signal Types Advantages of “S-video” connection over composite (RCA) connector: • Separates luminance information from color information to increase B&W resolution • Fewer artifacts with modern video sources like DSS and DVD
Video Review - Signal Types Advantage of Component vs. “S-video”: • Increased color resolution
Video Review - Signal Types Advantage of RGB over component: • RGB signals correspond directly to the CRT guns / light sources • Provides best possible picture quality for analog CRT displays HDTV uses component rather than RGB: • Requires less bandwidth • More content can be stored on a DVD or broadcast.
Video Review - Signal Types Advantage of DVI vs. Component: • DVI is digital equivalent of analog RGB • DVI better for fixed pixel (non-CRT) displays connected to digital sources (DVD, digital cable set top converter, video games) • Removes unnecessary analog-digital-analog conversion - enables pure digital signal to display • DVI has bandwidth to address each pixel in a digital TV display individually - enabling the highest possible picture quality • Component better for analog (CRT) displays - analog has theoretically better color and luminance range
Video Review - Resolution • Measure of maximum number of light to dark transitions produced horizontally or vertically • Horizontal resolution usually expressed in pixels • Vertical resolution expressed in pixels or lines
Light & Color Theory • Light is electromagnetic energy within a narrow range of frequencies • Each different wavelength of light energy (if seen alone) is perceived by the human eye/brain as a different, fully saturated, color
Light & Color Theory • If light from the sun is equally reflected from a surface, the eye/brain sees the surface as white. • If a surface absorbs all light energy and reflects none, the surface appears black.
Light & Color Theory • If more than one wavelength is reflected, the eye/brain performs a mixing of all light energy present and perceives a single color which is a result of the mixture.
Human Vision • Eye is tri-stimulus - sees light using red, green, & blue receptors • Each receptor has a different response to the light spectrum • CIE Standard Observer Response Curve shows average response of each receptor across light spectrum
Human Vision Three characteristics define how our eye/brain sees light:
Human Vision • Hue: Dominant wavelength, color or tint of the color.
Human Vision • Saturation: Degree of purity from light of other wavelengths (zero saturation = white; equal energy of all wavelengths)
Human Vision • Brightness: Perceived light energy level
Light & Color Measurement Light Measurement Units: Luminance (brightness): • Footlambert: U.S. unit of luminance (radiated light), 1 lumen per square foot • Nit (cd/m2): S.I. unit of luminance (radiated light), 1 candelaper square meter Illuminance: ambient light that illuminates the display • contributes to luminance that is observed from the image display • reduces the contrast in the image • need to block from measurement
Light & Color Measurement Light Measurement Units: Color (hue and saturation): • CIE chromaticity coordinates (x,y): From 1931 CIE Chromaticity Diagram (Kelly Chart) What color?
Color Measurement CIE Chromaticity Diagram • Graphically depicts the relationship between hue and saturation. • Diagram shows the pure spectral colors around the curved border • The results of mixing any of these spectral colors are shown at the base and center of the diagram.
Color Measurement How do video displays make white? • By combining the proper mix of RGB • All three guns are turned on to make white
Color Measurement • C.I.E. coordinate x = 0.313 y = 0.329 (D) is the white color which was chosen as the standard white reference for all video display systems. (D6500)
Color Measurement How do video displays make black? • All three guns are turned off to make black. • The same point on the chart represents white and black
Color Measurement How do video displays make color? • Using RGB light sources • Any three colors not lying on a straight line with one another are color primaries. • The points shown are the NTSC specified CRT phosphor color primaries for US televisions. • The connecting triangle encloses the range of colors able to be produced by a CRT using these color phosphors.
Color Measurement Color Temperature • Color Temperature is sometimes also used to specify different near-white colors. • Color Temperature is referenced to color of carbon when heated to different temperatures (measured in °Kelvin -- °Celsius plus 273).
Color Measurement • Different “whites”correspond to different color temperatures • White sheet of paper looks different under different light • CRT radiates light so color temperature not affected by lighting conditions (but brightness and contrast are)
Color Measurement • There is an approximate correlation between color temperature and CIE chromaticity • Accurate calibration is done using CIE coordinates
Color Measurement • Colors which are created by heating carbon form a continuous line across the CIE Chromaticity Diagram - known as the black body curve. • Only colors exactly on the curve are specified by original absolute color temperature.
Calibration Overview 1. Calibrate Display Geometry • Size • Centering • Pincushion • Trapezoid • Rotation • Linearity
Calibration Overview 2. Calibrate Display Convergence • Precisely overlay red, green, and blue images at all points on display. • Eliminate all color fringing effects.
Calibration Overview 3. Calibrate Display White Balance • Use color analyzer to measure “color” of white in center white window at high and low luminance levels
Calibration Overview 4. Calibrate Display User Controls • Brightness (Black Level) • Contrast (White Level) • Color (Saturation) • Tint (Hue) • Sharpness
Video Generator Introducing the VP400 & 401 ‘VideoPro’ The VP400 & 401 ‘VideoPro’ Multimedia video generators deliver the HDTV, NTSC, RGB, DVI & RF Video Signals You Need for Accurate Service & Alignments of Monitors & Direct View Displays.
Video Generator DVI (VP401) NTSC RF (VP401) Battery operated (8 hours) Component/RGB VESA/HDTV Composite S-Video
Video Generator SMPTE Bar Check and adjust color level and hue controls. Check color demodulator accuracy.
Video Generator Color Bar Check for primary (red, green, blue) and secondary (cyan, magenta, yellow) colors to confirm proper chroma processing.
Video Generator Focus Check for proper static & dynamic focus operation at screen center & edges.
Video Generator Crosshatch (4:3) Check and adjust convergence and linearity.
Video Generator Anamorphic Check accuracy of widescreen stretch feature (from 4:3 to 16:9).
Video Generator Overscan 5% overscan (green line) 10% overscan (red line) electrical center Check and adjust display geometry, including picture centering, size, trapezoid (keystone) correction, pincushion (bow) correction, and linearity.