Exam next week Covers everything about all sensory modalities except hearing This includes: vision balance/touch/taste/smell/ proprioception/theroception

COLOR VISION

Color Vision Perceiving Color Primary colors Red Green Blue

Trichromatic Theory of Color Vision Signal to Brain Wavelength Input Cone “Blue” Blue “Green” “Red”

Trichromatic Theory of Color Vision Signal to Brain Wavelength Input Cone “Blue” “Green” Green “Red”

Trichromatic Theory of Color Vision Signal to Brain Wavelength Input Cone “Blue” “Green” “Red” Red

Trichromatic Theory of Color Vision Signal to Brain Wavelength Input Cone “Blue” Equal Parts Red and Green = “Green” Yellow “Red”

Trichromatic Theory of Color Vision Signal to Brain Wavelength Input Cone “Blue” Equal Parts Red and Green = “Green” Yellow “Red”

Trichromatic Theory of Color Vision Signal to Brain Wavelength Input Cone “Blue” Equal Parts Red and Green = “Green” Yellow “Red”

Theories of Color Vision: Trichromatic Theory Problem with Trichromatic Theory: YELLOW

Theories of Color Vision: Opponent-Process Theory color is determined by outputs of two different continuously variable channels: red - green opponent channel blue - yellow opponent channel

Theories of Color Vision: Opponent-Process Theory Red opposes Green (Red + Green) opposes Blue Opponent-Process Theory explains color afterimages because the “opposite” of blue is yellow, the “opposite” of green is red, etc.

Color is an illusion Everything you’ve learned so far is wrong.

Color is an illusion Everything you’ve learned so far is wrong. Well, not really wrong, just far from complete.

Everthing you thought you knew L A N D Everthing you thought you knew about color is wrong...

What Newton Found (and everyone believed) White light can be split into all wavelengths by a prism According to previous theories: two wavelengths combine to yield intermediate color and no others Red Light Green Light Red + Green = YELLOW

What Newton Found (and everyone believed) White light can be split into all wavelengths by a prism According to previous theories: two wavelengths combine to yield intermediate color and no others Red + Green light can never yield blue Blue + Green light can never yield red

What twist did Land do to this paradigm that confounds the conventional understanding of color mixing?

What Land found: Two bands (colors) of the spectrum recombine to produce all the possible colors provided the appropriate relative amount of each wavelength is projected Red Light Green Light transparency slides

How did Land project the “appropriate” ratio of wavelengths?

Short- and Long- “record” Camera Capture two grey-scale images of the scene using filters that allow only the wavelengths you will project “Long” filter Object “short” filter film Projector Image “Long” filter “short” filter

Camera splits image into maps of “longer” and “shorter” wavelengths long filter medium filter

Projector combines “longer” and “shorter” wavelengths using the maps to get the appropriate amounts of each long/“red” light medium/ “green” light Viewer perceives desaturated hues including blues

What is Land’s interpretation? How do we perceive color?

Land’s interpretation: perception of color is a weighing of the ratio of shorter and longer wavelengths

Land’s interpretation: perception of color is a weighing of the ratio of shorter and longer wavelengths

Why would the visual system have evolved this way?

Why would the visual system have evolved this way? Hint: “Within broad limits, the actual values of the wavelengths make no difference, nor does the over-all available brightness of each”

What is color for? What is color vision used for? Identification - what is this thing? Discrimination - what other things is this thing like? Communication - indicates this thing to others But in each case color refers not to the illuminating light, but to the surface of the object itself

What is color for? Does the color of an object remain constant under different lighting conditions?

Color Constancy The “color” of objects is independent of the ambient light – even though light can vary dramatically Sunlight Incandescent Light Relative Intensity Relative Intensity Wavelength

Color Constancy Because of our mechanism of color constancy we can even use completely artificial spectra

Color Constancy The “color” of objects is independent of the ambient light

Next Time ATTENTION!