Color in Scientific Visualization
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1 Color in Scientific Visualization Mike Bailey, PhD San Diego Supercomputer Center and University of California at San Diego sdsc.edu 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 Tufte
2 The Electromagnetic Spectrum Blue: 380 nm Red: 780 nm Green: 520 nm The Human Eye Lens Retina Optic nerve
3 ~7,000,000 Cones Concentrated near the center of the retina Sensitive to high, medium, and low wavelengths Afterimages
4 Afterimages Color Receptors in the Cones Area of Spectrum: Wavelength: Approx. color: Low 560 nm Red Medium 530 nm Green High 420 nm Blue
5 Combinations of Color To The Brain H R - G M B - Y L Luminance How Many Shades of Different Colors Are We Able to Detect?
6
7 How Many Colors Do You Really Need? It depends if you want to do shading... Color # Shades # Bits Green Red Blue 64 6
8 ~115,000,000 Rods Concentrated on the periphery of the retina Sensitive to intensity Most sensitive at 500 nm (~green) How Many Pixels Do You Need? A person with 20/20 vision has a visual acuity of: 1 arc-minute = 1/60 Density = 1 DΘ =1/60 = R Viewing Distance (inches) Required Pixel Density (ppi) x monitor 16 monitor
9 Additive Colors Additive Color (RGB)
10 RGB Color Space Cyan White Green Yellow Blue Magenta Black Red Digital 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 2K 2 to 32K 2 Many different film heads available: Polaroid, 16mm movies, 35mm slides and movies, 4x5 and 8x10 transparencies, 70mm movies (for IMAX and Omnimax)
11 Digital Film Recorders Click! From Computer B Click! High-resolution grayscale monitor G R Color wheel Camera Click! Lasergraphics Digital Film Recorder
12 Is There a More Intuitive Way To Do Additive Colors Than RGB? Hue White Saturation Value Black To convert from HSV to RGB, see: Foley, Van Dam, Feiner, and Hughes, Computer Graphics: Principles and Practices, Addison-Wesley, Subtractive Colors
13 Subtractive Color (CMYK) CMY Color Space Red Black Magenta Blue White Yellow Cyan Green
14 Color Paper Printing Uses subtractive colors Uses 3 or 4 passes How Do Color Separations Work in Color Printing?
15
16 Printing the Four Colors Wax ( crayola ) Toner ( prism ) Toner ( skittles ) Sheets ( monet ) Color 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 products
17 CIE Chromaticity Diagram 520 nm y nm White Point nm x CIE Chromaticity Diagram 520 nm y C C D 780 nm White Point nm x
18 Color Gamut for an SGI Monitor Color CRT White Point Eye 0.50 y x Monitor White Color Gamut for a Monitor and Color Slides Color CRT y Slide White Projected Color Slides 0.20 Eye x White Point
19 Color Gamut for a Monitor and Color Printer 0.90 Color CRT y Color Paper Hardcopy 0.20 Eye x Image File Formats > 100 separate image file formats The SDSC Image Tools will deal with 30 of them Many hardcopy devices only accept PostScript
20 The SDSC Image Tools imconv file.rgb file.tif imscale -scale.45 file.rgb file.tif imstoryboard file1.tif file2.gif -outfile all.tif Printing at SDSC lpr -Pprism file.ps lpr -Pprism file.tif lpr -Jt -Pskittles file.tif SDSC color printers in order of increasing quality (and cost): crayola skittles starburst prism monet
21 Publishing Images on the WWW Images must be in GIF, JPG, or PNG format It is handy to create thumbnails of images to increase download speed imconv image.rgb image.jpg imscale -scale.30 image.rgb image.thumb.jpg <a href=image.jpg> <img src=image.thumb.jpg> </a> Some Good Rules of Thumb When Using Color for Scientific Visualization
22 What Makes a Good Contrast? Many people think simply adding color onto another color makes a good contrast In fact, a better measure is the luminance Knowing this also helps if someone makes a grayscale photocopy of your color hardcopy Color Alone Doesn t Cut It! Four score and seven years ago, our foreparents brought forth upon this continent a new nation, conceived in liberty, and dedicated to the proposition that all people are created equal. I sure hope that my life does not depend on being able to read this quickly and accurately!
23 Contrast is Crucial! Four score and seven years ago, our foreparents brought forth upon this continent a new nation, conceived in liberty, and dedicated to the proposition able to read that all this people are created equal. I would prefer that my life depend on being quickly and accurately! The Luminance Equation Y =.30*Red +.59*Green +.11*Blue
24 Luminance Table R G B Y Black White Red Green Blue Cyan Magenta Orange Yellow Contrast Table Black White Red Green Blue Cyan Magenta Orange Yellow Black White Red Green Blue Cyan Magenta Orange Yellow
25 Black Black Black Black Black Black Black Black Black White White White White White White White White White Red Red Red Red Red Red Red Red Red Yellow Yellow Yellow Yellow Yellow Yellow Yellow Yellow Yellow Green Green Green Green Green Green Green Green Green Blue Blue Blue Blue Blue Blue Blue Blue Blue Do Not Attempt to Fight Pre-Established Color Meanings
26 Pre-Established Color Meanings Red: Stop On Off Dangerous Hot High stress Oxygen Shallow Money loss Green: On Plants Carbon Moving Blue: Cool Safe Deep Nitrogen Use the Right Color Interpolation Method Gray scale Intensity Interpolation Saturation interpolation Two-color interpolation Rainbow scale Heated object interpolation
27 Gray Scale Intensity and Saturation Color Scales A National Center University for Computational of California, Science & Engineering San Diego
28 Two-Color Interpolation Rainbow Color Scale
29 Heated Object Color Scale Color Scale Contours
30 A Gallery of Color Scales Limit the Total Number of Colors if Viewers are to Discern Information Quickly Instructions: 1. Press red to logoff normally 2. Press light red to delete all your files, change your password to something random, and logoff You have 2 seconds
31 ? The Ability to Discriminate Colors Changes with Surrounding Color
32 The Ability to Discriminate Colors Changes with Surrounding Color A National Center University for Computational of California, Science & Engineering San Diego The Ability to Discriminate Colors Changes with Surrounding Color
33 Do Not Widely Separate Colors that Need to be Compared 1. Find the color on the right that matches the color on the left 2. If you select wrong, we will change your password to something random, and log you off You have 2 seconds
34
35 The Ability to Discriminate Colors Changes with Size of the Colored Area The Ability to Discriminate Colors Changes with Ambient Light
36 The Ability to Discriminate Colors Changes with the Age of the Viewer Beware of Mach Banding
37 Beware of Mach Banding Perceived Intens ity Actual Intens ity Beware of Mach Banding
38 Be Aware of Color Recognition Deficiencies Actually no such thing as color blindness ~10% of Caucasian men ~4% of non-caucasian men ~0.5% of women Code Information Redundantly Four score and seven years ago, our forefathers brought forth upon this continent a new nation... Four score and seven years ago, our forefathers brought forth upon this continent a new nation... Four score and seven years ago, our forefathers brought forth upon this continent a new nation...
39 Code Information Redundantly: Color + Different fonts Symbols Fill pattern Outline pattern Outline thickness This also helps if someone makes a grayscale photocopy of your color hardcopy Use a Black or White Line as the Boundary Between Colored Regions
40 Watch the Use of Saturated Blues for Fast-Moving Items or Fine Detail Watch the Use of Saturated Reds and Blues Together Reds Four and score Blues and seven are on years ago, our foreparents opposite brought forth ends upon of this the continent a new nation, color conceived in liberty, and dedicated spectrum. to the It is proposition that all people hard are created for your equal. eyes to focus on both.
41 Watch the Use of Saturated Reds and Blues Together Do Not Display High Spatial Frequencies in Color
42 Be Aware of the Differences Between Color Gamuts Color Gamut for a Monitor and Color Printer 0.90 Color CRT y Color Paper Hardcopy 0.20 Eye x
43 Color-Preserving and Contrast-Preserving Mappings Monitor colors to be printed ?? White Point Some Basic Rules for Understanding the Limitations of NTSC Video
44 Understand the Limitations of going from Workstations to NTSC Use less saturated colors due to color gamut considerations Expect an effective resolution of (at best) ~640x480 Do not use single-pixel thick lines Stay away from the edges of the screen Some colors have better video resolution than others NTSC Cycles of Encoding per Scanline What: Cycles/Scanline: Intensity 267 Orange-Blue 96 Purple-Green 35
45 Only You Can Prevent Color Pollution Just because you have 2 24 different colors, doesn t mean you must use them all Good Color and Perception References Roy Hall, Illumination and Color in Computer Generated Imagery, Springer-Verlag, R. Daniel Overheim and David Wagner, Light and Color, John Wiley & Sons, David Travis, Effective Color Displays, Academic Press, L.G. Thorell and W.J. Smith, Using Computer Color Effectively, Prentice Hall, Edward Tufte, The Visual Display of Quantitative Information, Graphics Press, Edward Tufte, Envisioning Information, Graphics Press, Edward Tufte, Visual Explanations, Graphics Press, Howard Resnikoff, The Illusion of Reality, Springer-Verlag, 1989.
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