Chapter 5 (colour) Flashcards
White paper
High reflectance, light bounces back
What is lightness reflects cd?
Illusions
Actual reflectance of surfaces in world, perception of light reflected on each surface regardless of light variations
Chocolate bar
Low reflectance, light is absorbed
Color consistency
Is achieved when visual system choices lightness consistency by applying assumptions about the way light sources and surfaces interact in the world, thus the illusion is perceived
What is color consistency?
Disconnecting effects of lighting conditions to determine true color of object
After images
Result from operation of of opponent process in visual system
3 types of output for after images
- Red green
- Blue yellow
- Black white
Mechanisms of after images
Visual system contains some cells that get excited by red light and inhibited by green light and visa versa
Results of after images
Eye is still firing colors even when color disappears
Some R- +G cells firing faster than R + G- cells hence why not seeing the plain white square
What causes color blindness?
Congenital absence of 1 come ( usually L or M cone in males)
Cone types
L come- long wavelength
M come- medium wavelength
S cone- short wavelength
Mechanisms of color blindness
Not blind to differences in wave length but color perception is based off outputs of 2 cones instead of 3
Folded card illusion
Visual system assumes changes in luminance are due to lighting shifts caused by folds in card not changed in surface reflection
Lab example of folded card illusion
Folded card looks as if light source is coming from above
Bumps and dimples
Visuals system makes 2 assumptions:
- portion of surface that faces towards light source will be brighter than portion away from light
- assume light source is coming from above
Checkerboard shadow illusion
Visual system is not able to disregard interpretation of light sources in scenes when making judgements about the brightness of surface
Color perception definition
Color is our subjective wavelength that perception ends up bouncing off the object and into our retina
How is color perception transferred in eye?
- Photoreceptors start process by selectively responding to different wave lengths
- 3 different cone receptors used for the color (trichromacy)
- Then 3 comes translate into opponent process mechanisms (like red vs green of blue vs yellow) which is responsible for after images
What is the purpose of the visual system?
- to tell us what is out there rather than the wavelengths
- take into account the luminance characteristics of a scene to tell us the actual colors in the world ( color constancy)
