Chapter 5- Flashcards
What are the 3 steps to color perception?
1) Detection-wavelengths must be detected
2) Discrimination-We must be able to tel the difference between one wavelength
3) Appearance - We want to assign perceived colors to lights and surfaces in the world
S-cone
a cone that is preferentially sensitive to short wavelengths (420nm)- blue cone
M-cones
A cone that is preferentially sensitive to middle wavelengths: Colloquially but not entirely known as (535nm) green cone
L-Cone
A cone that is preferentially sensitive to long wavelengths -(565nm) “red cone”
Isaac Newton
- “Light does not have color, we internally perceive color”
What are typical light sources?
Most of the light we see is reflected: Sun, Light bulb, fire
What range of the electromagnetic spectrum is visible light?
400-700nm
Newtons theory : wrong
Seven Kinds of light–> seven kinds of photoreceptors
Thomas Young’s Theory- right
Continuum of light –> three kinds of photoreceptors (not including rods)
Photopic
Light intensities that are bright enough to stimulate the cone receptors and bright enough to saturate the rod receptors to their maximum responses
*Ex: Sunlight and bright indoor lighting are both photopic light conditions
Scotopic
Light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate the cone receptors
*Ex: moonlight and extremely dim indoor lighting are both scotopic light conditions
Color Discrimination: The principle of Univariance
photoreceptors can only respond more or less depending on how many quanta they have absorbed –Cannot whisper in your ear what the wavelengths of quanta were.
CONES ARE COLORBLIND
Rods
only sensitive to scotopic levels
- All rods contain the same photopigment molecule: Rhodopsin
- rods have the same sensitivity to various wavelengths of light
Metamer
-perceptually identical but not identical
One receptor system
One receptor type, one light=match
two receptor types, two lights =match
Rule: Output= input sensitivity
Trichromacy
The theory that the color of any light is defined in our visual system by the relationships of three numbers, the outputs of three receptors types now known to be the three cones
Additive color mixing
- shine lights together to see what they create
ex: Blue plus yellow lights create white wavelengths
pointilism - painting
- technology
- dots of color
- eyes blur color to see certain colors (additive color)
Subtractive color mixing: A mixture of pigments
taking light away
-yellow backpack- absorb blue light
Color Space
A three dimensional space that describes all the colors
-RGB color space
HSB color space
RGB color Space
Defined by the outputs of long medium and short wavelengths lights (ie red green, blue)
HSB color space
defined by hue saturation and brightness
Hue- the chromatic color aspect
saturation-the chromatic strength of a hue
brightness- the distance from clack in color space
Color Opposites
Red vs green
blue vs yellow
dark vs light
Opponent color theory
The theory that perception of color depends on the output of three mechanisms: each of them based on an opponency between two colors: red-green, blue– yellow black-white
s
ganglion cell projecting to fovea -
Legal vs illegal colors
-Ewald Hering (1834-1918)
can have: bluish green reddish yellow, but never have reddish green or bluish yellow
Does everyone see colors the same way?
NO
male population 8% colorblind
female population .05%
color anomalous
Deuteranope
Absence of M-cones-green
Protanope Color Blindess
Due to absence of L-cones -red
Tritanope
Due to absence of S-cones -blue
Cone monochromat
Has only one cone type-truly color blind
Achromatopsia
An inability to perceive colors that is caused by central nervous system
Related color
Brown or gray
Unrelated color
A color that can be experienced in isolation
Luminance
The visual system knows that light changes but not hue
Mantis Shrimp
-16 receptor types
