Colour Flashcards
Colour subtraction
Subtracting (absorbing) parts of the spectrum of light present in ordinary white light, by means of coloured pigments
What colour would you see when directing a white light through both the red filter and the green filter?
Black
This is because a pure red filter only allows through red light and a pure green filter only allows through green light. Together this means that they allow no light and appear black
What is the 3 receptor basis of colour vision?
possessing of three independent channels for conveying colour information, derived from the three different types of cone cells in the eye:
green, red and blue
Colors perceived are determined by differing proportions of excitation in the three cones types.
What is the problem of colour constancy?
A particular wavelength combination reflected from a surface (and the particular combination of excitation in the three cone types) can yield experience of different colours in different situations.
True or false?
Receptive fields and the expectation that colour perceived would reflect only the light coming from the patch in question.
True
Reflected light is a property of what?
The environment
The visual system, via the cones detects what?
Reflected light and interprets the light-energy as colour.
Define colour constancy
Our ability to perceive different objects as always having the same colour independently of where we see them, or in what lighting conditions.
Why are artificial fluorescent lights are yellowish to white
That is, the wavelengths of light generated by a light bulb is yellow
What part of the brain has the parts most important for vision and where is it located?
Occipital lobe and at the back of the brain
What part of the occipital lobe is imprortant for vision?
The visual cortex
What do cells found in the first part of the visual cortex - area V1 do?
They respond to a certain combination of wavelengths of light
They sum up the different cones’ excitation with a different weight for each cone
Where do V1 cells get there input from?
photoreceptors
From area V1 the cells project (send fibres - axons) which other visual area? and via what area?
What do cells do in this area?
V4 via V2
Cells respond in more complex fashion, in a way that corresponds more to the perceived colour of an object.
They have activity that parallels our conscious experience
What area is constancy apparent in?
Constancy is not apparent in area V1, but it is in area V4
In terms of colour constancy, perceived colour of an object depends not only on the relative amount it excites the three kinds of cones but…
but also on the relative amount it excites the objects around it
(relative brightness in each of the three cone channels)
by considering the overall balance of cone excitation across multiple objects, the visual system is able to compensate for the colour of the light.
When white light is beamed through a prism what happens?
The prism separates the white light into the different wavelengths of which it is composed, which we perceive as different colours.
Longer wavelengths bend more or less than shorter wavelengths?
Less
Big car turning round a corner is harder
the wavelengths of visible light range from about?
10-6 to 10-7m
What is a nanometer?
a billionth (10-9) of a metre and is usually abbreviated nm (1 m = 1,000,000,000 nm).
True or false?
Different wavelengths in the visible range of the electromagnetic spectrum correspond to different colours (hues).
True
ultraviolet, blue, green, orange, infared
The colours of surfaces are determined by?
the wavelength composition of the light reflected off the surface.
Why does a black surface look black?
Because it absorbs all the visible wavelengths of light falling (or incident) on the surface, so there is no light reflected.
Why does a white surface look white?
It reflects all the visible wavelengths in the incident light
