“Land Mondrian”
What Newton Found (and
everyone believed)
• White light can be split into all wavelengths by a
prism
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 = YELLOW
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
transparency slides
How did Land project the
“appropriate” ratio of
wavelengths?
Short- and Long- “record”
Camera
• Capture two greyscale images of the
scene using filters
that allow only the
wavelengths you
will project
“Long” filter
Object
“short” filter
film
Projector
“Long” filter
“short” filter
Image
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 this design?
Why would the visual system
have this design?
• Hint: “Within broad limits, the actual values of
the wavelengths make no difference, nor does
the over-all available brightness of each”
Color Constancy
• The “color” of objects is independent of the
ambient light
– yellow bananas and green leaves look yellow
and green regardless of whether they are
viewed in direct sunlight or by the light of a fire
Color Constancy
• Land Mondrian:
– demonstration of color constancy: all the
wavelengths of the colored squares are shifted
by the same amount into the blue end of the
spectrum - your brain ignores the shift
Color Constancy
• Tricky question:
– why does a window look blue from the outside
when there’s a TV going inside?
Color Constancy
• Tricky question:
– why does a window look blue from the outside
when there’s a TV going inside?
– The wavelengths emitted by a TV are mostly in
the blue end of the spectrum
Color Constancy
• Really Tricky question:
– why doesn’t a TV look blue?
– Color Constancy causes you to perceive the
areas of the screen with the greatest proportion
of long wavelengths as “red”, the greatest
proportion of short wavelengths as “blue” and
everything else in between.
About the Exam…
• The practice test is still available
• Remember: when given “yes” or “no”,
“true” or “false”, or any such choice, you
have to select one or the other!
• Read questions carefully - think through the
answers carefully
Next Time: Attention
• Heads up: Treismann article on Wednesday
or Thursday of next week