L5 - colour vision Flashcards
what is colour perception?
allows distinction between surfaces of the same brightness
What does isoluminant mean?
same brightness
What does achromatic mean?
without colour
what are the physical properties of colour perception?
wavelength + intensity
What are the 2 functions of colour perception?
Signalling e.g., yellow bananas indicate ripeness
Detection e.g., picking cherries is easier with colour perception as some objects stand out fur to their colour
What wavelength does blue have?
450-490 nm
what wavelength does green have?
500-575 nm
what wavelength does red have?
620-700 nm
What has to happen for white to be produced?
A mix of all wavelengths
what is black?
an absence of light
what is reflectance?
objects are seen due light reflection
e.g., a red apple reflects red light and absorbs other colours, making it appear red to our eyes
What does a reflectance curve do?
shows the composition of light reflected by an object.
what’s chromatic light?
Light that has colour, it consists of specific wavelengths that are. more prominent that others, giving it a distinct hue.
e.g., The light from a blue LED is chromatic light because it is predominantly blue in colour
what’s monochromatic light?
Light that consists of a single wavelength or colour
e.g., laser light is often monochromatic because it emits light at a specific wavelength.
A red laser pointer emits monochromatic light at a wavelength around 650 nm, appearing as pure red.
What is achromatic light?
Light that has no colour –> includes shades of white, gray and black.
No hue –> doesn’t favour any wavelength
e.g., white light from standard light bulb as it contains all wavelengths of visible in equal measure.
what’s additive colour mixing?
the process of creating new colours by combining different colours of light
e.g., using light in the 3 primary colours can be used in various ways to create other colours incl combining all of them to produce white light.
what’s subtractive mixing?
the process of creating colours by combining different pigments, dyes or inks, each of which absorbs (subtracts) certain wavelengths of light + reflects others
e.g., using light in colours cyan, magenta and yellow removes wavelengths from white light - producing new colours.
Mixing these colours together theoretically results in black
What are the 3 types of cone photoreceptors
S-cones: maximal absorption at short wavelengths (blue)
M-cones: maximal absorption at medium wavelengths (green)
L-cones: maximal absorption at long wavelengths (red)
What does density refer to in cone photoreceptors
cones are concentrated around the fovea - resulting in poorer colour discrimination in the periphery.
What is opponent process theory?
Theory colour vision that explains how colours are processed at a neurological level after being detected by the cone photoreceptors in the retina.
Proposed by Ewald Hering
What are the 3 types of colour deficiencies?
Protanope - missing long wavelengths
Deuteranope - missing medium wavelengths
Tritanope - missing short wavelengths
What’s colour constancy?
the ability to perceive the colour of an object consistently under varying lighting conditions.
