Colour part 1 Flashcards
Why do we perceive colour? give examples
Signalling information about natural and human built environment (traffic lights, and bananas)
Perceptual organization of the world (where one object begins and the other one ends)
Object recognition (apple types)
Cultural transmission (used to represent ideas in society)
Aesthetics
What are the two things we see for colour?
Wavelengths of light
Pure wavelengths (monochromatic light) –> laser –> narrow band of wavelength
What is the region for visible light?
400-700 nm
What are reflective curves?
Shows how much light is reflected off an object at different wavelengths?
Is the light off an object just one wavelength?
No, lots of wavelengths
What would the reflectance curve look like for lettuce and tomato?
Lettuce = more green reflected (MED wavelength)
Tomato = more red reflected (Long)
Still a distribution of wavelengths
What would the reflectance curve look like for white paper?
lots of all colours reflected –> equal across spectrum
What would the reflectance curve look like for gray paper?
equal but low reflectance
What would the reflectance curve look like for black
paper?
Doesn’t reflect much
What is extreme black called (0.2% reflectance)?
Vantablack S-VIS
What are the primary colours?
Depends on what you are doing with colour
Just need 3 colours that are spaced along spectrum
What are the colours used for printing?
Cyan, magenta, yellow
What is reflection and subtractive colour mixing with paint?
Colour a paint looks depends on reflectance
What wavelengths does yellow pain reflect?
Long and medium
What wavelengths does blue pain reflect?
Small and medium
What if you combine blue and yellow pain?
only reflects what yellow and blue both reflect = so medium
What model does transmission and additive colour mixing use?
RGB colour model
Is the RGB colour model opposite to CMY?
Yes
What happens when all the colours in RGB are overlapped?
white
What is transmission?
admitting light rather than absorbing like computer screens
What model do LCD computer screens use and how do they work?
RGB
Each pixel has red, green, and blue piece = relative brightness determines what we see
How to describe the full range of colours?
a 3 dimensional colour space
How many colours can humans discriminate?
at least 2 million
What are the three dimensions of the first colour space
Hue, saturation and value (HSV colour space)
What is hue?
The chromatic or rainbow colour
What is saturation?
The amount of white added (to the particular hue)
What is value?
How light or dark the colour is
What are 2 other versions of colour space?
HSL (hue, saturation, lightness), RGB (red, green, blue)
What is hue, saturation and lightness in the HSL colour space?
Hue is the same, saturation is how grey, and lightness is how light
Do you always need 3 dimensions for colour space?
yes
How does red, green, blue colour space work?
For computer
How much of each colour is turned on for each pixel
ratio of each colour
What could colours be?
Percepts
Qualia
Patterns of neural activity
Properties of objects in the world
What is qualia?
The “redness” of red
unarticulable essence of colour
What is the inverted spectrum argument?
How do I know my red is your red or maybe your red is like my green
What is the trichromatic theory based on?
Colour perception is based on 3 principal colours
Colour perception is based on 3 receptor types (cones)
Colour perception is a 3 dimentional construct
What is the experiment to support the trichromatic theory?
color matching experiments
How does the the color matching experiments work?
Participants tries to match test field by adjusting the brightness of lights shining on comparison field
Exactly 3 lights of different wavelengths are necessary to match all test field colours
The participant can make it look identical to test field
What colours does the colour matching experiment use?
RGB
What are the three types of cones
Short (blue), medium (green) long (yellow)
How do cones respond to colours of single wavelengths?
480 nm light causes activation of all 3 cones
relative level of activation of each cone type gives colour information to brain
What does white do to cone activation?
all three
What are metamers?
two different stimuli that are perceptually identical
Identical cone activation
How do metamers work?
if you get a combo of the light that does the same activation of each cone type –> metamers
Total activation of each type of cone is identical –> looks the same
s= 0.2 + s= 0.8 = 1.0 total
