Lecture 5 & 6 Flashcards
What does colour enhance?
Perceptual organisation
Top down control
Automatic bottom up processing
Colours for wavelengths: short/medium medium medium/long long
blue
green
yellow
red
What are the colours of solid objects?
Reflected wavelengths
Chromatic colours are the result of selective reflection (some reflected others absorbed)
Achromatic colours are the result of equal reflection
Colours of transparent objects
Chromatic colours are the result of selective transmission (some colours absorbed and some transmitted)
3 Colour dimensions in terms of Hue, Saturation and brightness
Hue: colour wheel
Saturation: amount of white added to the colour
Brightness: The amount of light reflected/intensity of the light
Mixing light
Additive colour mixture, combination of wavelengths
Mixing pigments
Subtractive colour mixture. Pigments will absorb the same wavelengths they absorb when they are alone. Only wavelengths reflected that are common in both pigments
Theories of colour
Trichromatic theory
Opponent process theory
Trichromatic theory
Young & Hemlhots
Colour matching experiments.
Results of trichromatic theory
Any colour can be matched by correctly adjusting 3 different wavelengths, not 2. Full colour vision is based on the ability to combine 3 wavelengths.
Physiological evidence of trichromatic theory
S = short wavelengths M = medium wavelengths L = long wavelengths
Monochromatism
No functioning cones so only perceive shades of brightness
Dichromatism
Protanopia (no L cones)
Deuteranopia (no M cones)
Tritanopia (no S cones)
Tetrachromacy
Some animals have 4 types of cones so have 4 dimensional colour space
Opponent process theory
Hering complementary afterimages Adapting " generates " afterimages blue => yellow green => red black => white
What opponent channels respond in opposite ways to different wavelengths?
Black/white
Red/green
Blue/yellow
Resulting in these as blindness
Oculomotor cues
Cues that include accommodation and convergence. Body related cues
What are stimulus related cues?
monocular cues (with one eye) binocular cue (both eyes)
What are involved in monocular cues?
Occlusion, relative height, relative size, perspective convergence, familiar size, atmospheric pressure, texture gradients, shadows
Occlusion (monocular cues)
occluded objects (partially hidden) appear further away
Relative height (monocular cue)
Objects higher in the visual field are further away than objects in the lower field.
Relative size (monocular cues)
when objects are equal in size the one that is further away takes up less of the visual field
Familiar size (monocular cue)
knowledge about physical size of an object
Perspective convergence
converging parts of an object are further away
Atmospheric pressure
Objects that are further away are less sharp and have a blue tint. Particles in the atmosphere scatter light and soften colours.
Texture gradients
Denser textures indicate objects are further away
Motion based cues
motion parallax (near objects move quicky and far away objects move slowly), deletion and accretion
Deletion and accretion
an object being covered and uncovered is further away. If you look at something in the distance and you move the object also appears to move
Depth cues
Body related
Stimulus related
Binocular cues
Binocular cues
Retinal disparity and stereoscopic vision
Retinal disparity
The retinal images in the left and right eyes are a few cm apart
Horopter
Imaginary plane through the fixation point connecting all objects of which retinal images fall on corresponding retinal points
Stereopsis
The ability to use retinal disparity as a cue to perceive depth. The larger the disparity the further away the object is from fixation.
Ponzo illusion
Two objects that are the same size appear different sizes in images due to their relative location. The size of an object is determined by its degree of visual angle.
Calculating size constancy
S = K ( R X D)
S perceived size
R size of the retinal image
D perceived distance
