overview of colour vision Flashcards
what is the definition of radiation?
radiation is emission of small packets of energy called photons that travel at the speed of light
What is the difference between high and low-energy photons
high energy photons vibrate at high frequency, short wavelength. vice versa
what is scotopic, mesopic, and photopic vision, describe the rod saturation and rod/cone threshold- when they occur ie moonlight, starlight, indoor lighting, complete darkness
scotopic vision: rod vision from complete darkness to starlight
Mesopic: this is where cone threshold begins and some rods are iin use during moonlight
photopic-cone vision this is where rod saturates and cones take over
what is unit of measurement of Light as radiant energy
watts per metre squared
what is luminance
is radiant energy but scaled to spectral sensitivity of the human eye as everyone’s spec- sensitivity differs slightly
what is the signal response when the equivalent intensity of light in terms of watts per meter squared refers to red for example, when looking at different regions of the retina with different photoreceptor sensitivity?
that photoreceptors sensitive to red/ long wavelength will respond greatly compared to those that are less sensitive to that wavelength.
what are the 3 spectral classes of cone that human vision depend on
Blue, green and red; more correctly
termed SW, MW and LW cones
what does the summed photoreceptor signal determine as opposed to a single response?
Summed photoreceptor signals
determine luminous sensitivity over
the visible spectrum, ie brightness, so the greater the summed signal, the greater the luminance or brightness
what is a hue?
colour appearance, which changes from blue to green to yellow to red as wavelength increases
what is the difference between spectral colours and non-spectral colors?
spec colours are elicited by a single wavelength of light- and are part of the visible spectrum
non spec- is a combination of diff wavelengths
what is surface spectral
reflectance
- Objects appear coloured due to the wavelength composition of the light reflected
from the surface - The SSR is a fixed physical or chemical property of a surface
- SSR describes the proportion of light reflected at each wavelength of the visible
spectrum
different object have different ssr, and each ssr reflect diff proportions of wavelengths, hence provide different colour perception ( if it were an orange object it will reflect more m/l wavelength of light)
what is wavelength discrimination?
the ability to identify differences in wavelength between objects independently of changes in intensity or light source
what is achromaticity
refers to the absence of a colour, it is not a hue. it is the perception of lightness without the quality of colour like white, black and grey-not an actual colour (without colour)
Is wavelength discrimination possible with
a single spectrally-tuned photoreceptor?
No.
For example, a low intensity at 560 could produce the same response as a higher intensity 450- wont be able to tell if this change is due to changes in intensity or wavelength; hence why requires at least two spectral classes of cones to be able to discriminate wavelength from intensity changes
Cannot disentangle wavelength and intensity; a single photoreceptor is colour blind
what does the phototransduction signal depend on
depends on rate of photon absorption.
photons with higher energy (shorter wavelengths) are absorbed more readily than photons with lower energy (longer wavelengths).
