Transcript Polar Connections

Digital Color Basics
Rob Snyder
June 2011
Our Eyes are Light Detectors!
Our eyes have two types of photoreceptors called
rods and cones. These cells are located in the retina
layer at the back of the eye.
Rods are used to see in very dim light and only
show the world to us in black and white. This is why
you see only black and white when you are outside
after dark or in a dimly lit room.
Cones allow us to see colors. They are not as
sensitive as the rods so they only work in bright
light.
There are three types of cones in the human eye.
Long wavelength cones have a peak detection of greenish-yellow.
Medium wavelength cones have a peak detection of green .
Short wavelength cones detect principally blue and violet colors.
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/colcon.html#c1
Color processing that begins in retinas
continues in the brain
Source: http://en.wikipedia.org/wiki/Color_vision
Analyzing Digital Images (ADI) computer software can
be used to analyze colors detected by digital camera.
The Eye/Camera Analogy
A digital camera can be compared and contrasted
with our eyes. It has a sensor that also detects the
intensities of light in the red, green, and blue portions of
the electromagnetic spectrum.
The ADI Software/Brain Analogy
ADI software can be compared and
contrasted with our brain. The software
interprets data it receives from three
different sensors in a camera.
Our brain employs an opponent process
where differences in the responses of cones
are interpreted.
Red, Green, and Blue are commonly referred to
as the primary colors of light
Note: Any 3 colors from three different regions of the visible
spectrum can be primary colors.
There are many ways to show students
how primary colors of light can be mixed.
The University of New Hampshire’s Measuring Vegetative Health web
site has interesting Quick Time movies.
http://mvh.sr.unh.edu/mvhinvestigations/red_green.htm
Inexpensive floodlights also can be used
to mix colors of light.
Shining two primary colors of light of equal intensity
onto a screen produces pure complementary colors.
cyan
yellow
magenta
Use a data table predict what colors of light must be mixed
to produce there complementary colors.
ADI has a rectangle tool that can analyze what happens
when blue and green floodlights shine onto a screen.
R = 2%, G = 70%, B = 62% Almost a pure cyan color.
A second data table can be used to record observations.
Red and Blue Floodlights
produce a magenta color.
R = 62%, G = 25%, B = 60% A fairly good magenta color.
Red and Green floodlights
produce a yellow color.
R = 63%, G = 51%, B = 34% Not a very pure yellow color.
Red, Green, and Blue floodlights
produce a white color.
R = 60%, G = 58%, B = 59% Not very white.
Red light has the lowest frequency in the visible
spectrum. Green light has a middle frequency. Blue
light has a higher frequency.
Light from the different frequency regions can
combine to form white light. Therefore, primary
colors of light are referred to as additive primary
colors.
Any three colors from each of the three
frequency regions of the visible portion of the
electromagnetic spectrum can be additive primary
colors.
Students are often introduced primary colors by
mixing blue, red, and yellow paints or food dyes.
As is true with light, other colors can be primary colors.
Cyan, Magenta, and Yellow are a set of primary
pigments often used by artists and in printing.
What happens if you mix colors of paint or dye?
Some of you will mix blue, red, and yellow acrylic
paints from Michaels ($1.49 a bottle).
Some of you will mix cyan, magenta, and yellow
acrylic paints from a art supply store ($7 to $10 a
tube).
Some of you will mix blue, red, and yellow food
dye.
The Analyze Paint and Dye Colors
document describes how to:
 Paint a swatch of each primary color on art paper.
 Mix the three primary colors together and paint a
swatch on art paper.
 Take a photograph of the swatches of paint or dye
color.
 Upload the photograph to a file on a computer.
 Open ADI software.
 Upload the photograph of colors to ADI software.
 Use the rectangle tool to analyze the colors.
What did you discover when you used the
rectangle tool to analyze paint or dye colors?.
What did you discover
about yellow paint or dye?.
R = 62%, G = 45%, B = 0% Not quite a pure yellow.
Primary colors of paints and pigments
are called subtractive primary colors.
Red paint absorbs blue and green light. Blue paint
absorbs red and green light. Yellow paint absorbs blue
and violet. Mixing these three primary colors of paint
results in a muddy dark brown color. This means that
not all wavelengths of incident light were absorbed.
Cyan absorbs red light. Yellow absorbs blue light.
Magenta absorbs green light. A mix of equal amounts of
each of these primary colors results in a black color.
That means that all wavelengths of incident light were
absorbed.
How is the mixing of paints or pigments
different from the mixing of colors of light?
How can you determine that a group of colors
of paint are primary colors?
How can you determine that a group of colors
of light are primary colors?