Light, Colour, and Displays CPSC 453 Fall 2018 Sonny Chan - - PowerPoint PPT Presentation

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Light, Colour, and Displays CPSC 453 Fall 2018 Sonny Chan - - PowerPoint PPT Presentation

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Light, Colour, and Displays CPSC 453 Fall 2018 Sonny Chan Announcements Assignment #1 released! Written component due Monday, Sept. 17 Programming component due Tuesday, Sept. 25 Tutorial sessions have started, hopefully you

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Light, Colour, and Displays

CPSC 453 – Fall 2018 Sonny Chan

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Announcements

  • Assignment #1 released!
  • Written component due Monday, Sept. 17
  • Programming component due Tuesday, Sept. 25
  • Tutorial sessions have started, hopefully you went!
  • Ask questions on piazza to get quickest reply
  • We’ll still answer email or D2L if you prefer
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The Written Component

  • Designed to help you think about the problems before

you write your code

  • Not meant to take up a lot of time
  • Show your work to get credit!
  • A single sentence, short paragraph, or couple of

equations will usually suffice

  • Submit scan or (good) photograph of work on D2L
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Outline for Today

  • Light
  • Colour
  • Displays
  • Resolution
  • Images

Ready?

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–Genesis 1:3

And God said, “Let there be light,” and there was light.

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Our first curiosity

  • What are these “temperature” settings we keep seeing
  • n our cameras and displays?

camera settings display settings

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What is

light?

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James Clark Maxwell

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[xkcd.org]

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What about photons?

Complicated question…

[S. Tanzilli]

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Where does light

come from?

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Black-Body Radiation

  • An opaque, non-reflective body in thermodynamic

equilibrium emits electromagnetic radiation with a spectrum dependent only on its temperature

  • Planck’s Radiation Law
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How hot is

the sun?

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Colour

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What colour is this ball?

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Is it orange?

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What exactly do we mean by

“orange”?

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Human Colour Perception

  • On our retina, we have two types of photoreceptors, rods

and cones, that are sensitive to electromagnetic radiation

[xrite.com]

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[webvision.med.utah.edu]

Are we equally sensitive to different visible wavelengths?

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[webvision.med.utah.edu]

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Figure 4. False color images showing the arrangement of L (red), M (green), and S (blue) cones in the retinas of different

[H. Hofer et al., J. Neuroscience 25(42), 2005]

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Luminous Efficiency

  • Humans perceive colour differences

much more acutely within certain wavelengths! 420nm 450nm 590nm 620nm

[courtesy of K. Breeden, Stanford University]

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Colour Blindness

Ishihara test for cone defect

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Perception of Colour

  • Revisiting our original question: what is “orange”?
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Do we perceive the same colour? No.

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Graphics Displays

Not only these…

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Graphics Displays

… but these too!

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What are the

primary colours?

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Back to Colour Perception

  • Our goal: stimulate photoreceptors in some combination

How about these? Or these?

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A Contemporary Liquid Crystal Display

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Magnified LCD

A display “pixel”

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LCDs

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Additive Colour Blending

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Can we display all perceptible colours?

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Colour Matching

… isn’t always possible!

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Standard RGB Gamut

In the CIE colour space

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What about these graphics displays?

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What is

white light?

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What kind of light do these things emit?

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Colour Reflection

[courtesy of K. Breeden, Stanford University]

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R+G = ???

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Subtractive Colour Blending

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Colour Printing

How do we control luminance?

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Halftones

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Primary Colours

Was your first grade teacher right?

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Resolution

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Does your smart phone have the same resolution as your high definition TV?

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What units

is resolution measured in?

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Human Visual Acuity

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Human Visual Acuity

[telescope-optics.net]

Highest visual resolution is about

  • ne arc minute

(1/60 of a degree)

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So how many pixels do we actually need?

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Let’s try a quick exercise

How many pixels do we need?

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Does your smart phone have the same resolution as your high definition TV?

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What is a digital

image?

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A record of something we (may) observe?

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Digital Images

  • Two key elements:
  • Colour
  • usually R, G, B
  • can be C, M, Y, K
  • Resolution
  • samples, or “pixels”, arranged

in a two-dimensional grid

  • may or may not correspond to

pixels on a display

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The discipline concerned with generating or manipulating visual imagery using computational devices and methods.

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Things to Remember

  • Light is just another form of electromagnetic radiation
  • Colour is in the eye of the beholder
  • Displays are engineered to human visual perception
  • Resolution is not (necessarily) measured in pixels
  • Digital images are the goal of computer graphics