Overview of colour vision Flashcards
Describe light as electromagnetic radiation
- Light as a wave and equation:
wavelength = speed of light / frequenc
What are photons
Radiation is emitted from a source in small packets of energy = photons
what speed do photons travel at?
speed of light
how do photons vibrate?
Photons vibrate at a frequency that increases with their energy
what is frequency?
the number of cycles per second pass a given point
describe the electromagnetic spectrum
as you go right wavelength increase and as you go left frequency increases
high energy photons vibrate…
at high frequency; shorter wavelength
what is visible light on the EM spectrum
narrow band
how does light quality vary?
-along 2 dimensions
-intensity and wavelength or chromaticity
what is intensity?
-can be measured as energy (watts/unit area)
-relates to brightness in visible spectrum
what is wavelength/chromaticity?
relates to colour
how to measure light as radiant energy?
can be measured in watts/m^2
how to measure light as luminance?
candela/m^2
-scaled by interaction conventions according to spectral sensitivity of human eye
how to measure light as photon flux (quantal flux)?
- photons per unit area per unit time
- on the longer wavelength end
- stimulus intensity
Brightness is the same as luminance. TRUE OR FALSE
FALSE
what is hue?
Hue = colour appearance, which changes from blue to green to yellow to red as wavelength increases
what are spectral colours?
Spectral colours are those that can be elicited by single wavelength
what are non-spectral colours?
Many colours cannot be equated with specific wavelengths: purple, pink, brown… black, white (non-spectral)
what does colour depend on?
Colour depends on wavelength but cannot simply be equated with wavelength
what does colour vision entail?
Colour vision entails the ability to see colours and discriminate objects on the basis of colour
describe colour as surface spectral reflectance
-Objects appear coloured due to the wavelength composition of the light reflected from the surface
- The SSR is a fixed physical/chemical property of a surface
- SSR describes the proportion of light reflected at each wavelength of the visible spectrum
Is SSR the physical property that corresponds to colour?
Coloured objects do not reflect a single wavelength corresponding to a spectral colour
colour appearance depends…?
Colour appearance depends on the relative amount of different wavelength
Quality of the visible spectrum depends on …?
- an organisms spectral sensitivity
- e.g. humans have rather low sensitivity to wavelengths <400 nm
- Wavelength. Chromaticity or perceived hue, changes with wavelength
- signalled by comparison of cone signals