CS349 - Implementing User Interfaces - Spring 2010

Public Service Annoucements

1. Assignment 4.

Lecture 34 - Display Properties

Human Vision

Eye & Brain

Psychophysical Properties

Spatial Acuity

Cone mosaic

• cones gather light from a finte area
• cones are spaced by about 0.008 degrees in the fovea

At the optometrist

• 20/20 vision means being able to see a gap of

At the psychophysicist

Hyperacuity

The cone mosaic is not ordered, but random.

• phase processing is possible
• much finer resolutions, not limited by receptor size
• another order of magnitude in resolution.

Temporal Acuity

Eye integrates over a temporal window about 30 msec long.

`Full Size' Displays

Display Types

Serial versus Parallel Displays

Reflective versus Self-Luminous

• Reflective remove light
  • digital paper, which is LCD with a mirror instead of a backlight
• Self-luminous add light
  • television is inherently self-luminous
  • LCD removes light

Resolution

Temporal

Spatial

• 4 pixels per millimeter (used to be three, etc.)
• At a distance of 700 mm this is 0.02 degrees.
  • fine for television where viewing distance is longer
    • high definition television: 1500 pixels per metre, 1.5 pixels per mm
    • 2 metre viewing distance 0.02 deg.

Small Displays

Apple Retina Display

• the display of the iPhone 4
• liquid crystal, backlit with LED backlight
  • not OLED,
  • Why? OLED about 10% efficient; LED close to 100% efficient: Apple likes white backgrounds
• 3" by 2" (75mm by 50mm)
• 960 by 640 pixels
• 326 pixels per inch
  • 13 pixels per mm
  • "Apple engineers developed pixels so small, a mere 78 micrometers, across that the human eye can't distinguish individual pixels."
• roughly 200 mm viewing distance
  • pixel spacing is 0.022 degrees
  • under optimal resolution we can resolve things down to 0.005 degrees
    • At 200mm 0.005deg is 18 microns
    • Viewing distance assumed above must be 800mm
  • with hyperacuity the same test gives a viewing distance of 2400 mm.

Colour

Conservativism of photoreceptors

Human colour perception is a recent development

• and probably not too important for survival, at least for men
• on the X chromosome, so many men have colour vision defects.

Photoreceptor pigment mutated into three different molecules

• long ago yellow split from blue
• recently, among primates, yellow split into red and green

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• CS349 - Spring 2010
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• Bill Cowan's home page.