II-1mjb – January 7, 2008Oregon State UniversityComputer GraphicsUsing Color inScientific VisualizationMike BaileyOregon State Universitymjb – January 7, 2008Oregon State UniversityComputer Graphics “The often scant benefits derived from coloring data indicate that even putting a good color in a good place is a complex matter. Indeed, so difficult and subtle that avoiding catastrophe becomes the first principle in bringing color to information. Above all, do no harm.”–Edward TufteII-2mjb – January 7, 2008Oregon State UniversityComputer GraphicsWhat’s Wrong with this Picture?Source:Scientific American, June 2000mjb – January 7, 2008Oregon State UniversityComputer GraphicsThe Human EyeOptic nerveRetinaLensII-3mjb – January 7, 2008Oregon State UniversityComputer GraphicsCones• ~7,000,000• Concentrated near the center of the retina• Sensitive to high, medium, and low wavelengthsmjb – January 7, 2008Oregon State UniversityComputer GraphicsThe Electromagnetic SpectrumBlue: 380 nmGreen: 520 nmRed: 780 nmII-4mjb – January 7, 2008Oregon State UniversityComputer GraphicsColor Receptors in the ConesLowMediumHighArea of Spectrum:Wavelength: Approx. color:560 nm530 nm420 nmRedGreenBluemjb – January 7, 2008Oregon State UniversityComputer GraphicsCombinations of Color To The BrainHMLR - GB - YLuminanceII-5mjb – January 7, 2008Oregon State UniversityComputer GraphicsHow Many Shades of Different ColorsAre We Able to Detect?mjb – January 7, 2008Oregon State UniversityComputer GraphicsII-6mjb – January 7, 2008Oregon State UniversityComputer Graphicsmjb – January 7, 2008Oregon State UniversityComputer GraphicsII-7mjb – January 7, 2008Oregon State UniversityComputer GraphicsRods• ~115,000,000• Concentrated on the periphery of the retina• Sensitive to intensity• Most sensitive at 500 nm (~green)mjb – January 7, 2008Oregon State UniversityComputer GraphicsII-8mjb – January 7, 2008Oregon State UniversityComputer GraphicsSidebar: How Many Pixels Do You Need?A person with 20/20 vision has a visual acuity of:1 arc-minute = 1/60°36 9531 11124 14312 28694006600Viewing Distance(inches)RequiredPixel Density(ppi)Density = ΘD1Θ=1/60°=.00029R19” monitor16” monitor1280x1024mjb – January 7, 2008Oregon State UniversityComputer GraphicsMonitors: Additive ColorsII-9mjb – January 7, 2008Oregon State UniversityComputer GraphicsAdditive Color (RGB)mjb – January 7, 2008Oregon State UniversityComputer GraphicsRGB Color SpaceRedGreenBlueMagentaCyanYellowWhiteBlackII-10mjb – January 7, 2008Oregon State UniversityComputer GraphicsDigital Film RecordersClick!Click!Click!High-resolution grayscale monitorColor wheelCameraFromComputerRBGmjb – January 7, 2008Oregon State UniversityComputer GraphicsDigital Film Recorders• Use additive colors• Output resolution is limited by the quality of a grayscale monitor, not your display• Typical resolutions currently available range from 2K2to 32K2• Many different film heads available: Polaroid, 16mm movies, 35mm slides and movies, 4x5 and 8x10 transparencies, 70mm movies (for IMAX and Omnimax)II-11mjb – January 7, 2008Oregon State UniversityComputer GraphicsLasergraphics Digital Film Recordermjb – January 7, 2008Oregon State UniversityComputer GraphicsIs There a More Intuitive Way To Do Additive Colors Than RGB?HueValueBlackWhitefloat hsv[3], rgb[3];HsvRgb( hsv, rgb );0. ≤ s, v, r, g, b ≤ 1.0. ≤ h ≤ 360.SaturationII-12mjb – January 7, 2008Oregon State UniversityComputer GraphicsSubtractive Colorsmjb – January 7, 2008Oregon State UniversityComputer GraphicsSubtractive Color (CMYK)II-13mjb – January 7, 2008Oregon State UniversityComputer GraphicsCMY Color SpaceRedGreenBlueMagentaCyanYellowWhiteBlackmjb – January 7, 2008Oregon State UniversityComputer GraphicsColor Paper Printing• Uses subtractive colors• Uses 3 or 4 passesII-14mjb – January 7, 2008Oregon State UniversityComputer GraphicsHow Do Color Separations Work in Color Printing?Source: R. Daniel Overheim and David Wagner, Light and Color, John Wiley & Sons, 1982.mjb – January 7, 2008Oregon State UniversityComputer GraphicsII-15mjb – January 7, 2008Oregon State UniversityComputer Graphicsmjb – January 7, 2008Oregon State UniversityComputer GraphicsPrinting the Four ColorsWaxTonerTonerSheetsII-16mjb – January 7, 2008Oregon State UniversityComputer GraphicsColor Paper Printing• Uses subtractive colors• Uses 3 or 4 passes• Resolution ranges from 200 DPI to 600 DPI• Considerable variation in quality between products• Considerable variation in color gamut between productsmjb – January 7, 2008Oregon State UniversityComputer GraphicsCIE Chromaticity Diagramy0.000.100.200.300.400.500.600.700.800.90x0.00 0.20 0.40 0.60 0.80White Point380 nm780 nm520 nmII-17mjb – January 7, 2008Oregon State UniversityComputer GraphicsCIE Chromaticity Diagramy0.000.100.200.300.400.500.600.700.800.90x0.00 0.20 0.40 0.60 0.80White Point380 nm780 nm520 nmCDC'mjb – January 7, 2008Oregon State UniversityComputer GraphicsColor Gamut for an SGI MonitorEyeColor CRTWhite PointMonitor Whitey0.000.100.200.300.400.500.600.700.800.90x0.00 0.20 0.40 0.60 0.80II-18mjb – January 7, 2008Oregon State UniversityComputer GraphicsColor Gamut for a Monitorand Color SlidesEyeColor CRTProjected Color SlidesWhite PointSlide Whitey0.000.100.200.300.400.500.600.700.800.90x0.00 0.20 0.40 0.60 0.80mjb – January 7, 2008Oregon State UniversityComputer GraphicsColor Gamut for a Monitorand Color PrinterEyeColor CRTColor Paper Hardcopyy0.000.100.200.300.400.500.600.700.800.90x0.00 0.20 0.40 0.60 0.80II-19mjb – January 7, 2008Oregon State UniversityComputer GraphicsLa*b* DiagramWhite Point380 nm780 nm520 nmOSU Logomjb – January 7, 2008Oregon State UniversityComputer GraphicsLa*b* DiagramII-20mjb – January 7, 2008Oregon State UniversityComputer GraphicsSome Good Rules of Thumb When Using Color for Scientific Visualizationmjb – January 7, 2008Oregon State UniversityComputer GraphicsWhat Makes a Good Contrast?• Many people think simply adding color onto another color makes a good contrast• In fact, a better measure is the Δ luminance• Knowing this also helps if someone makes a grayscale photocopy of your color hardcopyII-21mjb – January 7, 2008Oregon State UniversityComputer GraphicsColor Alone Doesn’t Cut It !Four score and seven years ago, our foreparentsbrought forth upon thiscontinent a new nation, conceived in liberty, anddedicated to