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

Reading for Next TimeFCG Chap 3 Raster Algorithms (except 3.2-3.4, 3.8) FCG Section 2.11 Triangles

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

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

Review: Trichromacy and Metamersthree types of conescolor is combination of cone stimulimetamer: identically perceived color caused by very different spectra

Review: Measured vs. CIE Color Spacesmeasured basismonochromatic lightsphysical observationsnegative lobestransformed basisimaginary lightsall positive, unit areaY is luminance

Review: Chromaticity Diagram and Gamutsplane of equal brightness showing chromaticitygamut is polygon, device primaries at cornersdefines reproducible color range

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

Vision/Color II

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

HSV and RGBHSV/HSI conversion from RGBnot expressible in matrix

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

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

Opponent Colordefinitionachromatic axisR-G and Y-B axisseparate lightness from chroma channelsfirst level encodinglinear combination of LMSbefore optic nervebasis for perceptiondefines color blindness

vischeck.comsimulates color vision deficienciesDeuteranopeProtanopeTritanopeNormal vision

Adaptation, Surrounding Colorcolor perception is also affected byadaptation (move from sunlight to dark room)surrounding color/intensity:simultaneous contrast effect

Color/Lightness ConstancyImage courtesy of John McCann

Color/Lightness ConstancyImage courtesy of John McCann

Color Constancyautomatic white balance from change in illuminationvast amount of processing behind the scenes!colorimetry vs. perception

Stroop Effectsay what the color is as fast as possible

redblueorangepurplegreen

Stroop Effectbluegreenpurpleredorange

interplay between cognition and perception

Virtual Trackball

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

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

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

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