Vision/Color II, Virtual Trackball Week 5, Wed Feb 7
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Transcript of Vision/Color II, Virtual Trackball Week 5, Wed Feb 7
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Reading for Last Time & TodayRB Chap Color
FCG Sections 3.2-3.3 FCG Chap 20 Color FCG Sections 21.2.2, 21.2.4
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Reading for Next TimeFCG Chap 3 Raster Algorithms (except 3.2-3.4, 3.8) FCG Section 2.11 Triangles
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Midterm Newsmidterm next time (Friday Feb 9)closed book, no calculatorsallowed to have one page of noteshandwritten, one side of 8.5x11 sheetthis room (DMP 301), 10-10:50material coveredtransformations, viewing/projection
sit where there is an examcell phones off
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Review: RGB Component Colorsimple model of color using RGB triplescomponent-wise multiplication(a0,a1,a2) * (b0,b1,b2) = (a0*b0, a1*b1, a2*b2)
why does this work?must dive into light, human vision, color spaces
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Review: Trichromacy and Metamersthree types of conescolor is combination of cone stimulimetamer: identically perceived color caused by very different spectra
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Review: Measured vs. CIE Color Spacesmeasured basismonochromatic lightsphysical observationsnegative lobestransformed basisimaginary lightsall positive, unit areaY is luminance
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Review: Chromaticity Diagram and Gamutsplane of equal brightness showing chromaticitygamut is polygon, device primaries at cornersdefines reproducible color range
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Review: RGB Color Space (Color Cube)define colors with (r, g, b) amounts of red, green, and blueused by OpenGLhardware-centric
RGB color cube sits within CIE color spacesubset of perceivable colorsscale, rotate, shear cube
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Vision/Color II
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HSV Color Spacemore intuitive color space for peopleH = Huedominant wavelength, colorS = Saturationhow far from grey/whiteV = Valuehow far from black/whiteaka brightness B, intensity I, lightness L
ValueSaturationHue
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HSV and RGBHSV/HSI conversion from RGBnot expressible in matrix
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YIQ Color Space color model used for color TVY is luminance (same as CIE)I & Q are color (not same I as HSI!)use Y only for B/W backwards compatibilityconversion from RGB is linear
green much lighter than redred lighter than blue
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Luminance vs. IntensityluminanceY of YIQ0.299R + 0.587G + 0.114Bintensity/brightness I/V/B of HSI/HSV/HSB0.333R + 0.333G + 0.333Bwww.csse.uwa.edu.au/~robyn/Visioncourse/colour/lecture/node5.html
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Opponent Colordefinitionachromatic axisR-G and Y-B axisseparate lightness from chroma channelsfirst level encodinglinear combination of LMSbefore optic nervebasis for perceptiondefines color blindness
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vischeck.comsimulates color vision deficienciesDeuteranopeProtanopeTritanopeNormal vision
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Adaptation, Surrounding Colorcolor perception is also affected byadaptation (move from sunlight to dark room)surrounding color/intensity:simultaneous contrast effect
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Color/Lightness ConstancyImage courtesy of John McCann
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Color/Lightness ConstancyImage courtesy of John McCann
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Color Constancyautomatic white balance from change in illuminationvast amount of processing behind the scenes!colorimetry vs. perception
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Stroop Effectsay what the color is as fast as possible
redblueorangepurplegreen
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Stroop Effectbluegreenpurpleredorange
interplay between cognition and perception
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Virtual Trackball
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Virtual Trackballinterface for spinning objects arounddrag mouse to control rotation of view volumeorbit/spin metaphorvs. flying/driving with lookatrolling glass trackballcenter at screen origin, surrounds worldhemisphere sticks up in z, out of screenrotate ball = spin world
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Virtual Trackballknow screen click: (x, 0, z)want to infer point on trackball: (x,y,z)ball is unit sphere, so ||x, y, z|| = 1.0solve for y
eyeimage plane
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Trackball Rotationcorrespondence:moving point on plane from (x, 0, z) to (a, 0, c)moving point on ball from p1 =(x, y, z) to p2 =(a, b, c) correspondence:translating mouse from p1 (mouse down) to p2 (mouse up)rotating about the axis n = p1 x p2
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Trackball Computationuser defines two pointsplace where first clicked p1 = (x, y, z) place where released p2 = (a, b, c) create plane from vectors between points, originaxis of rotation is plane normal: cross product (p1 - o) x (p2 - o): p1 x p2 if origin = (0,0,0)amount of rotation depends on angle between linesp1 p2 = |p1| |p2| cos q|p1 x p2 | = |p1| |p2| sin qcompute rotation matrix, use to rotate world
Better picture for opponent color Plane + line