l9- colour perception Flashcards
(26 cards)
NATURAL LIGHT + colour perception
natural light
- made of diff wavelengths
- monochromatic length (1 wavelength,640mm)=rare in nature
- every object reflects a mix of WLs
NATURAL LIGHT + colour perception
colour
- interaction between physical properties of object n visual system
photoreceptors in the retina
- 4 types: S-cones, rods, M-cones, L-cones
- WL sensitivty- each type responds to diff WL ranges
prinicple of univariance
- diff WL+intensity combos can make the same response from a photoreceptor
- photoreceptor only signals how much light it absorbs, not the wl
- 1 receptor cannot produce colour alone
trichromacy
colour vision
- depends on ratio of 3 cone outputs
- percieved colour depends on response of 3 cone types to object spectral reflectance
- any colour can be matched using a combo of 3 primary colours: red, green blue
trichromacy
trichromacy theory of colour vision
- young-helmholtz 1800s
- based on colour matching experiments
- validated by maxwell
- white or grey=percieved when 3 cone types=stimulated equally
trichromacy
metamers
- consequcne of univarence+trichromacy
- 2 or more mixs of lights look identical if they excite cones equally
- physically diff, perceptually equivalent
trichromacy
dichromacy + colour blindness
- have neutral point: single WL point appears white to them
- they only have 2 cone types
- result: fewer colour percieved; match colours w 2 primaries
trichromacy
types of dichromacy
D🍆Muncher+P🍆Lover= loses women. Toe suckers= lose STDs
- deuteranopia: miss M cones- lose red/orange/green
- protanopia: miss L-cones- lose red/orange/green
- tritanopia: miss S-cones- lose blue/yellow
trichromacy
other types of colour blindness
- colour anomalous: cone pigments too similiar
- monocular colour blindness: 1 eye only
- cone monochromat: 1 cone type only
- rod monochromat: only rods- no colours, poor acuity
- tetrachromocy: 4 cone types
- cortical colour deficiency: brain based colour loss (eg achromatopsia)
trichromacy
animal colour vision
- bees: UV-sensitive, trichromacy
- birds: tetrachromatic
- mantis shrimp: up to 16 photoreceptor types
trichromacy
colour spaces
- 3D structure: based on trichromacy vision
- LMS: based on cone outputs
- RGB: used in digital systems
- HSB: hue, saturation, brightness- rearrangement of RGB
- CIE XYZ: global standard using tristimulus values
- tristimulus values: percent of each primary needed to match a colour
trichromacy
additive mixing n colour models
- additive RGB: mixing light (eg red+green=yellow)
- HSB model: based on human colour perception
- CIE: defines spectral n non-spectral colours
- Nonspectral hues: mix of diff wavelengths
opponent colour theory
opponent colour theory
hering, 1800s
- opponent pairs: red/green, blue/yellow, black/white
- certain hues= mutually exclysive
- evidence: afterimages, colour contrast, hue cancellation
oponent colour theory s
opponent channels
- hue channels: L-M (red/green), S-(L+M) (blue/yellow)
- brightness channel=L+M
- saturation: ratio of hue channels to brightness channel
- neutral point: where opponent signals cancel out- appears grey
oponent colour theor
opponent Vs trichromatic theories
- trichromatic: photoreceptor level-light detection
- opponent: neural level- perception n comparison
- both: complementary not contradictory
oponent colour theor
colour opponecy in the brain
- sone opponent cells: in ganglion cells + LGN
- single opponent: broad colour areas
- double opponent: sensisitive to edges- in V1 n beyond
colour appearnace n constrancy
colour appearnace n constrancy
- context effects: perception depends on surrondings
- colour contrast: colour appears more intense opposite to its background
- colour assimilation: colours blend into surrondings
colour appearnace n constrancy
colour constancy
- percieved colour remains stable under different lighting
- lightness contancy: percieved reflectance remains stable
colour appearnace n constrancy
colour constancy key terms
- illuminace: incoming light
- reflectance: proportion of light reflected
- luminace: weighted reflected light
- brightness: percieved luminace
colour appearnace n constrancy
solving constancy
- problem= eye see luminace= illumination x reflectance
- solution= visual system discount illumiantion using:
- smooth light gradients
- full-spectrum lighting assumptions
- lighting form above n left
colour appearnace n constrancy
constancy illusions
- strawberries illusion: percieved as red due to illumiant discounting
- blue/gold dress: diff assumptions about lighting create diff colour perceptions
colour appearnace n constrancy
constancy vs contrast
- constancy: same colour percieved despite diff cone signals
- contrast: diff colour pereieved despite same cone signals
3 cones
L,S,M
L cones= long, red
M cones=medium, green
S cones=short, blue
