Victor Ostromoukhov Université de Montréal. Victor Ostromoukhov - Université de Montréal

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1 IFT3355 Victor Ostromoukhov Université de Montréal full world 2 1

2 in art history Mondrian 1921 The cave of Lascaux About BC Vermeer mid-xvii century 3 is one of the most effective visual attributes for coding information in displays and is capable, when used correctly, of achieving powerful and memorable effects Source: Lindsay W. MacDonald 4 2

3 A little color can be more effective than a lot Source: Lindsay W. MacDonald 5 Outline Introduction: What Is? Milestones in Understanding Management -Matching Curves CIE-XYZ Space CIE-LAB Space RGB Space Additive and Subtractive Mixture 6 3

4 What is? Electromagnetic Wave Spectral Power Distribution Reflectance Spectrum Illuminant D65 (nm) Spectral Power Distribution 7 What is? Neon Lamp Spectral Power Distribution Illuminant F1 Reflectance Spectrum Spectral Power Distribution Under D65 Spectral Power Distribution Under F1 8 4

5 What is? Observer Stimulus 9 What is? Ganglion Cells Bipolar Cells Horizontal Cells Rod Cone S M L Spectral Sensibility of the L, M and S Cones Light Light Amacrine Cells Retina Optic Nerve Rods Cones Distribution of Cones and Rods 10 5

6 What is? Visual Pathways [Palmer99] Right LGN Form Depth V2 Motion MT Depth Form Motion Depth Form Motion V1 LGN Left LGN Visual Cortex Form Depth Motion Retina LGN = Lateral Geniculate Nucleus 11 What and Where Subsystems Higher Visual Areas Where System: Motion Perception Depth Perception Spatial Organization Figure/Background Segregation Blind Fast High Contrast Sensitivity What System: Object Recognition Face Recognition Perception Selective Slow Low Contrast Sensitivity Midbrain Primary Visual Cortex [after Livingstone2002] 12 6

7 Newton 1672 Belongs to Both Great Traditions Rational Tradition: Discovery of Truly Primary s Theory if Light Mixture Pythagorean Tradition: is a Manifestation of the Harmony of the Celestial Spheres Studied Relations between s and Music 13 Maxwell 1867 Origins of modern quantitative color measurement (imetry) Experiences with Mixtures Psychological explanation of visual phenomena 14 7

8 von Helmholtz 1859: Trichromatic color theory Ancestor of the CIE-XYZ color space Violet Blue Green Yellow Orange Red Short wavelength receptors Medium wavelength receptors Long wavelength receptors Receptor Responses Violet Blue Green Yellow Orange Red Wavelengths (nm) 15 Hering 1874 Father of the opponent process color theory Focus on psychological interpretation of colors 16 8

9 Munsell 1905 System of visually uniform distribution of color patches Ancestor of CIE-LAB and CIE-LUV color spaces 17 Retinal Neural Interconnection 1900s Ramón y Cajal 1906 Nobel Prize 18 9

10 Neural Codes 1930s Hartline 1967 Nobel Prize Discovery of the mechanism of communication between the eye and the brain Lateral inhibition explained The horseshoe crab (Limulus polyphemus) The Hero Oscillogram of the electrical activity of a receptor unit in the lateral eye of Limulus From Hartline s Nobel Prize Lecture, December 12, Milestones s Hubel Wiesel 1981 Nobel Prize Discovery of complex receptive fields in the visual cortex Neural mechanisms of visual information processing Dark-field autoradiograph of striate cortex in an adult macaque, and reconstruction of layer Ivc. From Hubel s Nobel Prize Lecture, 8 December

11 imetry: CIE Matching Match a pure spectral test field w(λ) with a reference field: a mixture of red z(700), green y(546.1) and blue x(435.8) of variable intensity -matching curves x(λ) y(λ) z(λ) Test field w(λ) Reference field x(435.8) y(546.1) z(700) Test field w(λ) z(700) Reference field x(435.8) y(546.1) T = A + B + C T + C = A + B 21 CIE-XYZ Space -matching curves x(λ) y(λ) z(λ) 22 11

12 xyy Space 23 The s in the Chromaticity Diagram Spectrally pure colors (monochromatic or prismatic) on the contour Visible spectrum Neutral illuminant white Non-spectral colors (purples and magentas) no dominant wavelength 24 12

13 Perceptually Uniform Space: MacAdam In color space CIE-XYZ, the perceived distance between colors is not equal everywhere In perceptually uniform color space, Euclidean distances reflect perceived differences between colors MacAdam ellipses (areas of unperceivable differences) become circles Source: [Wyszecki and Stiles 82] 25 CIE-LAB Source: [Wyszecki and Stiles 82] 26 13

14 Gamut Mapping Typical CRT gamut 4-color CMYK printing gamut b* a* [Stollnitz, Ostromoukhov Salesin SIGGRAPH 98] Gamut mapping is a morphing of 3D color space according to adopted scheme 27 Pickers: HLS Apple s HLS wheel 28 14

15 RGB Space Simplified Calculations 29 Standard RGB (srgb) Space

16 Physical color mixture Additive red, green, blue Subtractive cyan, magenta, yellow Spot Lights Inks 31 Device-Dependent

17 Device-Independent 33 blindness protanopia bluish 8% male, 0.6% female Genetic Dichromate (2% male) One type of cone missing L (protanope) M (deuteranope) S (tritanope) Anomalous trichromat Shifted sensitivity bluish deuteranopia tritanopia greenish yellowish yellowish reddish Monochromatic colors perceived by a trichromat 34 17

18 blindness test A simple test permits to whether you are a trichromate or a dichromate People with anomalous cone pigmentation will fail to distinguish background from foreground 35 blind impressions 36 18