Lecture 13 Colour Flashcards
What indicated that different colours on the spectrum have different physical properties?
the fact that the degree to which beams from each part of the spectrum were bent by the second prism differed
When are chromatic colours (e.g. blue, green, red) perceived? Provide an example.
- when certain wavelengths are reflected by objects more than others –> SELECTIVE REFLECTION
- e.g. red paper reflecting long wavelengths (and absorbing short/medium)
When are achromatic colours (grey, black, white) perceived? Provide an example.
- when light is reflected equally across the spectrum
- e.g. white paper reflecting all wavelengths equally
What do reflectance curves plot?
percentage of light transmitted at each wavelength
What is the colour of transparent objects created by?
selective transmission
When does selective transmission occur? What kind of curve can be used to plot it?
- when only certain wavelengths pass THROUGH objects (e.g. cranberry juice selectively transmitting long wavelengths results in a reddish appearance)
- transmission curves
What colour is perceived with short, medium, long and medium, and long wavelengths?
- short = blue
- medium = green
- long and medium = yellow
- long = red
What is subtractive colour mixing?
- occurs when mixing together paints that have different pigments
- adding more pigments to a mixture results in fewer wavelengths being reflected (and more being absorbed)
Why does a mixture of blue and yellow paint appear green?
- blue reflects short wavelength (and SOME MEDIUM) and ABSORBS OTHERS
- yellow reflects long wavelength (and SOME MEDIUM) and ABSORBS OTHERS
- after combined, both pigments continue to reflect the same wavelengths they did on their own
- therefore, the only wavelengths that are reflected from a mixture of blue and yellow are MEDIUM wavelengths (i.e. green)
(SUBTRACTIVE)
What is additive colour mixing?
- occurs when mixing lights of different wavelengths
- all of the light that is reflected from the surface by each light when alone is also reflected when the lights are superimposed
Why does superimposing blue and yellow lights onto a whiteboard lead to the perception of white?
short (blue) + medium and long (yellow) wavelengths are ALL reflected back to our eyes, creating white
What are spectral colours?
those that appear on the spectrum
What are nonspectral colours?
can only be created by mixing spectral colours in various combinations (e.g. magenta by mixing red and blue)
what is hue?
another term for chromatic colour (blue, red, etc.) or ‘pure’ colour
What is value?
refers to the light-to-dark dimension
What is saturation?
determined by the amount of WHITE in a hue
TRUE or FALSE: more white = value decreasing, and more dark = desaturation
FALSE: more white = desaturation, and more dark = value decreasing
_______________ can be used to determine additive colour combinations.
HSV (hue/satuation/value) colour solids
What is the trichromatic theory?
states that all human colour vision is based on 3 principle colours (red, blue, green)
Describe the behavioural evidence for the trichromatic theory.
- observers with normal colour vision could match any reference wavelength by mixing the proportion of 3 wavelengths (red, green, and blue)
- > 3 were NEVER needed and 2 was sufficient to match some colours
- observers with colour deficiencies could match their perception of any colour with 2 wavelengths
- this meant that ‘normal’ colour vision depends on 3 receptor mechanisms (i.e. 3 types of cones)
What is the physiological evidence for trichromatic theory?
- visual pigments were found that respond maximally to short, medium, and long wavelengths
- colour perception is based on the combined responses of the 3 different types of cones, which vary depending on the wavelengths available
TRUE or FALSE: colour matching experiments show that colours that are perceptually similar can be caused by different combinations of various physical wavelengths.
TRUE
TRUE or FALSE: the cone pigments fire in an all or nothing response.
FALSE: cone pigment types differ in the PROPORTION OF LIGHT they absorb from particular parts of the light spectrum (i.e. short cones do not ONLY respond to blue)
Can one receptor type lead to colour vision?
NO - because any 2 wavelengths can cause same response in a monochromat simply by altering the intensity
