Visual Perception

Temporal Resolution (Flicker)

  • Critical Flicker Frequency (CFF) - when perception of intermittent light source changes from flickering light to conitnuous light
    • Perception of continous motion

Spatial Resolution (Visual Acuity)

  • The ability to distinguish individual pixels
    • We can see pixels larger than about 0.116 to 0.203mm

Colour Perception

  • Wavelength determines colour

  • There are two different colour sensors in a human eye

    • Cones - perceive colour (focus)
    • Rods - distinguish light from dark (peripheral vision)
    • Not evenly distributed; spatial resolution of visual field drops significantly at edges

  • 3 types of Cones means Trichromatic vision

  • We are more sensitive to differences in colour and brightness than absolute brightness levels

Colour Presentation

  • The ability to discriminate between colours depends on presentation
  • It's hard to tell colours apart when
    • The colours are pale
    • The object is small or thin
    • The colour patches are far apart

Colour Blindness

  • Monochromacity - 2 or 3 types of cones missing
  • Dischromacy - 1 type of cone missing
    • Protanopia - missing red cones
    • Deuteranopia - missing green cones
    • Tritanopia - missing blue cones

Colour Models

  • Additive - coloured light is added to produce white
    • e.g. RGB for displays
    • HSV/HSB to describe colour
  • Subtractive - coloured light is absorbed to produce black
    • e.g. CMY/CMYK - printing

HSV/HSB

  • Hue - determines colour (approximation of wavelength)
  • Saturation - how much hue (red <=> pink)

  • Value/Brightness - how much ligh is reflected

  • Value/brightness - reflecting light (less to more)

  • Saturation - containing hue (less to more)

Graphic Display Technology

  • Each pixel contains 3 sub-pixels (RGB)
    • Packed very closely together
    • Emits vary amounts of red, green, blue lights to produce different colours

LCD Displays

  • Uses liquid crystal and a polarising colour filters to display light
    • The filters controls the amount of light going through
  • Requires a backlight

OLED (Organic LED)

  • Individual glowing pixels
  • No backlight
  • Bendable

Digital Light Processing (DLP) Projectors

  • Digital micromirror device (DMD)
  • Shines light through a colour filter in between a condensing lens and a shaping lens
    • Reflected by the DMD and through another lens to project an image

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