Color to Binary Vision. The assignment Irfanview: A good utility Two parts: More challenging (Extra Credit) Lighting.

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1 Announcements Color to Binary Vision CSE 90-B Lecture 5 First assignment was available last Thursday Use whatever language you want. Link to matlab resources from web page Always check web page for updates on readings, etc. Discussion group for course is available as link from the course web page. Subscribe to class mailing list with send to majordomo@cs.ucsd.edu with body subscribe cse90-b my_ @something.something CSE90-B, Spring 2003 CSE90-B, Spring 2003 The assignment Irfanview: A good utility Two parts: For images. Color classification 2. Binary image processing More challenging (Extra Credit) Label Red pixels as Green Pixels as 2 Black pixels as 0 CSE90-B, Spring 2003 CSE90-B, Spring 2003 Other part: Binary Image Proccessing (Next lecture) Lighting Applied lighting can be represented as a function on the 4-D ray space (radiances) Special light sources Point sources Distant point sources Strip sources Area sources CSE90-B, Spring 2003 CSE90-B, Spring 2003

2 Camera s sensor BRDF Measured pixel intensity is a function of irradiance integrated over pixel s area over a range of wavelengths For some time Ideally, it s proportional to the radiance. I = t λ x y E( x, y, λ, t) s( x, y) q( λ) dydxdλ dt Bi-directional Reflectance Distribution Function ρ(θ in, φ in ; θ out, φ out ) Function of Incoming light direction: θ in, φ in Outgoing light direction: θ out, φ out Ratio of incident irradiance to emitted radiance (θ in,φ in ) ^n (θ out,φ out ) CSE90-B, Spring 2003 CSE90-B, Spring 2003 Robot Soccer The appearance of colors Color appearance is strongly affected by (at least): Spectrum of lighting striking the retina other nearby colors (space) adaptation to previous views (time) state of mind CSE90-B, Spring 2003 CSE90-B, Spring 2003 Light Spectrum Color Reflectance Measured color spectrum is a function of the spectrum of the illumination and reflectance CSE90-B, Spring 2003 CSE90-B, Spring 2003 From Foundations of Vision, Brian Wandell, 995, via B. Freeman slides

3 Illumination Spectra Color receptors Blue skylight Tungsten bulb Red cone Green cone Blue cone Response of k th cone = ρ ( λ) E( λ) dλ k CSE90-B, Spring 2003 From Foundations of Vision, Brian Wandell, 995, via B. Freeman slides CSE90-B, Spring 2003 RGB Color Cube Color spaces Block of colours for (r, g, b) in the range (0-). Convenient to have an upper bound on coefficient of each primary. In practice: primaries given by monitor phosphors (phosphors are the materials on the face of the monitor screen that glow when struck by electrons) Linear color spaces describe colors as linear combinations of primaries Choice of primaries=choice of color matching functions=choice of color space Color matching functions, hence color descriptions, are all within linear transformations RGB: primaries are monochromatic, energies are 645.2nm, 526.3nm, 444.4nm. Color matching functions have negative parts -> some colors can be matched only subtractively. CIE XYZ: Color matching functions are positive everywhere, but primaries are imaginary. Usually draw x, y, where x=x/(x+y+z) CSE90-B, Spring 2003 CSE90-B, Spring 2003 Color Matching Color matching functions Not on a computer Screen Choose primaries, say A, B, C E(λ) Given energy function, what amounts of primaries will match it? For each wavelength λ, determine how much of A, of B, and of C is needed to match light of that wavelength alone. a(λ) b(λ) c(λ) These are color matching functions Then our match is: { a(λ)e(λ)dλ }A + { b(λ)e(λ)dλ }B + { c(λ)e(λ)dλ }C CSE90-B, Spring 2003 CSE90-B, Spring 2003

4 RGB Color Matching RGB: primaries are monochromatic, energies are 645.2nm, 526.3nm, 444.4nm. Color matching functions have negative parts -> some colors can be matched only subtractively. CIE XYZ: Color matching functions are positive everywhere, but primaries are imaginary. Usually draw x, y, where x=x/(x+y+z) CSE90-B, Spring 2003 CSE90-B, Spring 2003 CIE XYZ Color Matching Functions CIE -XYZ and x-y CIE XYZ: Color matching functions are positive everywhere, but primaries are imaginary. Usually draw x, y, where x=x/(x+y+z) CSE90-B, Spring 2003 CSE90-B, Spring 2003 CIE xyy (Chromaticity Space) RGB to YIQ The YIQ system is the colour primary system adopted by NTSC for color television broadcasting. The YIQ color solid is formed by a linear transformation of the RGB cube. Its purpose is to exploit certain characteristics of the human visual system to maximize the use of a fixed bandwidth. [ Y ] [ ] [ R ] [ I ] = [ ] [ G ] [ Q ] [ ] [ B ] Note that Y captures intensity whereas I & Q capture the effects of hue & saturation. CSE90-B, Spring 2003 CSE90-B, Spring 2003

5 HSV Hexcone Hue, Saturation, Value AKA: Hue, Saturatation, Intensity (HIS) Metameric Lights (Metamers) Hexagon arises from projection of cube onto plane orthogonal to (R,G,B) = (,,) CSE90-B, Spring 2003 CSE90-B, Spring 2003 Blob Tracking for Robot Control Connected Regions CSE90-B, Spring 2003 What the connected regions in this binary image? Which regions are contained within which region? CSE90-B, Spring 2003 Connected Regions What the connected regions in this binary image? Which regions are contained within which region? CSE90-B, Spring 2003