CS781 - Colour for Computer Graphics - Winter 2009

Lecture 11

Visual Response to Light

Other interesting observations

  1. Basic colours
  2. Adaptation
  3. Simultaneous contrast

Measuring Colour

Two types of measurements

  1. Visual measurement
  2. Instrumental measurement.
    There are two things that we can measure
    1. psychophysical response to light
      • reproduce and improve on visual measurement
    2. physical properties of light
      • use results of psychophysical experiments
        • such as colour matching functions

        to calculate psychophysical response from physical measurements

Measuring physical properties

Almost always energy in the past,

Ultimate calibration is to heat

You now have a detector and a calibration.

Measuring a spectral power distribution

In principle, it is straightforward

  1. Split the light into a spectrum using
  2. Spectrum can be spread out in
  3. Get a stream of measurements

Current technology uses an array of detectors, but

Two aspects of calibration are hard

If an instrument is inexpensive they most likely skimped on calibration.

What can be measured?

Power of light emitted from a source in all directions

Power of light enitted from a source in a particular direction

Power of light falling on a surface

Power of light falling on a surface from a particular direction

Power of light leaving a surface

Power of light leaving a surface in a particular direction

Return to: