“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 LightGreen Light

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

Red LightGreen Light

How did Land project the “appropriate” ratio of

wavelengths?

Short- and Long- “record”

• Capture two grey-scale images of the scene using filters that allow only the wavelengths you will project

Camera

“short” filter

“Long” filter

film Projector

Object

Image“Long” filter

“short” filter

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