Cones and colour vision Flashcards
What are the maximum frequency wavelength for the different cone types?
Peaks:
L = 570nm
M = 535nm
S = 435nm
What are metamers?
2 lights that have different spectral power distributions but have the same appearance = Metameric matches
What assumption do we make on cones due to metamers?
We assume they stimulate all cone types equally.
What is an example of metameric match of colour.
If you were to match a green with a red you get yellow. That yellow is indistinguishable from a single monochromatic wavelength. So the eye doesn’t know if its pure yellow or yellow that has been made up of red and green.
What are the contemporary colours?
Red-Cyan
Blue-Yellow
How does brightness affect colour?
Brightness does not affect hue or saturation.
What are some features of the CIE colour space?
- Pure colours around the periphery.
- White in the center
- Saturation increases towards periphery
- Non spectral hues red to blue (the colours that require a combination of red and blue wavelengths)
- Line of black body radiation (When metal is heated and glows red then yellow, then white, then blue)
What is hue?
Hue is the specific shade or type of color we perceive, such as red, blue, green, or yellow. Dominant wavelength.
What is saturation?
The intensity or purity of a colour. How vivid or dull a color appears.
What is brightness?
How light or dark a colour appears. It does not affect hue or saturation but can influence how we perceive them.
What does colorimetry apply to?
Applies to small fields only
How does local colour vision work?
Colour is perceived in the central 5-10 degrees. The wavelength predicts colour. (e.g. red = long wavelengths, blue= short wavelengths)
How does global colour vision work?
Global colour vision is true colour perception and is influenced by surround.
Why do colours not change when illumination changes (i.e. from indoors to outdoors)?
This is due to colour constancy. The visual cortex automatically compensates for shifts in illumination so that colours do not change when illumination changes.
e.g. the dress illusion.
What are the results of colour mixing?
Red, Blue and Green are additive as it is light.
-Red + Blue = Magenta
-Red + Green = Yellow
-Green + Blue = Cyan
- We see white because the red, green and blue cones are equally stimulated.
Magenta, yellow, cyan are subtractive as they are paint. (Think printer)
-Cyan absorbs red and reflects blue and green
-Magenta absorbs green and reflects red and blue
- Yellow absorbs blue and reflects green and red.
- Combination of all 3 means red, green and blue are all absorbed and so no light is reflected resulting in us seeing black.
