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Human Perception. What you may or may not already know, want to know or even care about how you see. Goals. Decent understanding of human visual response Discuss intelligently about the flaws of current popular color systems Understand a few existing alternatives

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Human perception

Human Perception

What you may or may not already know, want to know or even care about how you see


Goals
Goals

  • Decent understanding of human visual response

  • Discuss intelligently about the flaws of current popular color systems

  • Understand a few existing alternatives

  • Completely redefine the way you look at the world, think about light, color, space-time and life in general


Outline
Outline

  • Human Eye

    • Anatomy

  • Reaction to light

    • Engineer’s perspective

    • Mathematician's View

  • Color Spaces

    • Brief History

    • CIE-XYZ, XYy, etc.

    • RGB

    • Recent work

  • Why Monitors Stink



Human eye 2
Human Eye 2

  • Rods and Cones

    • Cones see color

      • “red” “green” and “blue”

    • ~6.5 Million

      • 32% “red” 64% “green” 2% “blue”

    • High resolution - closely packed


Human eye 3
Human Eye 3

  • Rods and Cones

    • Rods don’t

    • May be excited by single photon

    • Respond to higher frequencies (blue/green)

    • Peripheral and night vision

      • Weird fact about sea captains

    • For the most part, we ignore rods


Outline1
Outline

  • Human Eye

    • Anatomy

  • Reaction to light

    • Engineer’s perspective

    • Mathematician's View

  • Color Spaces

    • Brief History

    • CIE-XYZ, XYy, etc.

    • RGB

    • Recent work

  • Why Monitors Stink


Reaction to light
Reaction to Light

  • For the Engineers:

Intensity

I = 0.299R + 0.587G + 0.114B

Input

Discuss later

Right now: “magic”

this is your brain

…Any questions?

Color


Reaction to light 2
Reaction to Light 2

  • For the mathematicians:

    • Several slides to follow to discuss sampling, lighting, integrating, linear algebra, etc

    • Be Prepared!



Math stuff 2
Math Stuff 2

  • Color is not “inherent” to a surface/object

  • Light source fires photons of varying wavelengths to object

  • Object reflects and absorbs different amounts of different wavelengths

  • Wavelengths reach cones on your eye

  • Integrated across response function



Math stuff 3
Math Stuff 3

  • What does this mean?

    • Think of a red laser on a “green” ball

      • Different light  Different color

    • All three cone types excited by each wavelength

      • nothing pure anymore?

    • Metamers


Math stuff 4
Math Stuff 4

  • If we consider the input from your eye to the “color unit” as linear algebra:

  • 3 independent (but not orthogonal) vectors

  • Can they span the “space”?


Outline2
Outline

  • Human Eye

    • Anatomy

  • Reaction to light

    • Engineer’s perspective

    • Mathematician's View

  • Color Spaces

    • Brief History

    • CIE-XYZ, XYy, etc.

    • RGB

    • Recent work

  • Why Monitors Stink


History
History

  • CIE – Commision Internationale de l'Éclairage

    • (aka International Commission on Illumination)

    • Established 1913

    • Color Standards 1931 and 1945

    • “Devoted to international cooperation on all matters relating to the science and art of lighting”


Cie stuff
CIE Stuff

  • CIE Standardized several color spaces:

    • XYZ – The “base” color space where X and Z are “color” variables and Y is “intensity”

      • Can be quickly integrated from wavelength values

    • XYy – The horseshoe we’ve all seen before


What s wrong with these
What’s wrong with these?

  • 1) They give the wrong impression


What s wrong with these 2
What’s wrong with these? 2

  • 2) They are trivariate

    • No metamers

  • 3) They do not describe the way light interacts in reality, but simplify it according to how the human eye perceives


From bad to worse
From bad to worse

  • RGB

    • Simplified version of CIE spaces

      • Values from 0..1

      • Used for I/O with CRT and LCD devices

    • So much interesting stuff happens “outside” of RGB space!


Recent work
Recent Work

  • [Meyer 1988]

    • Used Gaussian Quadrature to find 3 simulation wavelengths which most affect perception (called AC1C2 space)

  • [Johnson and Fairchild 1999]

    • Created a full spectral renderer to correctly discover metamerism, etc.

  • [Baxter, Wendt and Lin 2004]

    • Used 8 “sufficient” wavelengths to model subsurface scattering and absorption effects in paint (Really nice piece of work)


Outline3
Outline

  • Human Eye

    • Anatomy

  • Reaction to light

    • Engineer’s perspective

    • Mathematician's View

  • Color Spaces

    • Brief History

    • CIE-XYZ, XYy, etc.

    • RGB

    • Recent work

  • Why Monitors Stink


Monitors are bad
Monitors are Bad

  • Next time you are in your office, bring up a completely “white” screen and hold a piece of “white” paper next to it

  • Scan a (non-digital) photograph of a nice sunset…. Hold the original next to your monitor

  • Even better, look out at a sunset and compare it to your monitor


Thm take home message
THM–Take Home Message

  • Remember – Every man-made media has a viewable gamut and it doesn’t cover all visible light

  • Different lights make things different colors! (that’s why it looked so good at the store)

  • Trivariate spaces can only (sometimes) span the space of visible light, but can’t model the richness of ~400 wavelengths

  • There’s hope… listen to following speakers


References
References

  • Rochester Institute of Technology Munsell Color Science Laboratory: http://www.cis.rit.edu/mcsl/

  • http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html

  • http://www.netnam.vn/unescocourse/computervision/12.htm

  • http://www.cie-usnc.org/

  • Wavelength Selection for Synthetic Image Generation, Gary W. Meyer in Computer Vision, Graphics, and Image Processing 1988

  • Full Spectral Color Calculations in Realistic Image Synthesis, Garrett Johnson and Mark Fairchild in IEEE Computer Graphics and Applications 1999

  • IMPaSTo: A Realistic Interactive Model for Paint, Bill Baxter, Jeremy Wendt and Ming C. Lin in NonPhotorealistic Animation and Rendering 2004


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