Transcript Polar Connections

Detecting and Mixing Colors
STEM DIGITAL Institute
Rob Snyder
Many instruments can be used to
collect visible light data, including
digital cameras.
How do our eyes and digital
cameras detect colors of visible light?
Our Eyes Have Two Types of
Photoreceptors
Our eyes have two main types of photoreceptors
called rods and cones. These cells are located in a
layer at the back of the eye called the retina.
Cones allow us to see colors. They are not as
sensitive as the rods so they only work in bright light
and are often described as red, green and blue cones.
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 in
the evening or in a dimly lit room.
Each type of cone detects a range of wavelengths.
“Red” cones have a peak detection of greenish-yellow.
“Green” cones have a peak detection of green .
“Blue” cones detect principally blue and violet colors
Which pair of cones might respond when looking at a wall
that was painted the color yellow?
Color processing begins in the eye’s cones.
Signals are then transmitted through optic nerves to
the brain where data processing continues.
Our brain compares responses of cones to visible
light and interprets a color. For example: “Red” and
“green” cones both respond to yellow light.
Digital cameras have three types of filters that cover
an array of many sensors. The sensors detect the
intensities of light of long wavelengths (the red range ) or
medium wavelengths (the green range )or short
wavelengths (the blue range) that are transmitted
through the three different types of filters.
Data is then transmitted to and stored in a memory
card in the camera.
Recall that our RGB cones respond to a range
of wavelengths of light.
The RGB sensors of a digital camera also respond
to ranges of wavelengths of light.
The ADI Software/Brain Analogy
Our brain analyzes data
it receives from pairs of
“red”, “green”, and “blue”
cones in our eyes.
The ADI software
program in a computer
analyzes the responses of
the “red”, “green’ and
“blue” sensors in the
digital camera.
How can Analyzing Digital Images software
reveal the differences between primary colors of
light and primary colors of paints or pigments?
Here are two examples of primary
paints or pigments that can be mixed.
Cyan, Magenta, and Yellow
Elementary school students often learn
pigments are often used to print
that Blue, Red, and Yellow paints can
be used to create many colors.
many different colors.
The ADI “line tool” can reveal how sensors in a digital
camera respond to yellow paint.
The average intensities of colors detected along the line are:
Red = 62.3%, Green = 45.3%. Blue = 0.16%
ADI can generate a graph of the intensities of red,
green and blue intensities along a line.
The ADI Resources Document provides examples of
how to use the Line Tool.
The Line Tool: You can draw a line across an image and detect changes in the
intensities of red, green, and blue light.
 Select “Line Tool” and then move cursor to a Starting Point on the Photo
 Press down using left click to move the line to an end point and release.
 You can collect and record data about the start and end point of the line
and the average color intensities of the line.
Create a graph of colors along a line. Create a graph that shows changes in
the intensities of red, green, and blue light along a line that you draw across a
photograph.
 Use the File Menu in the upper left corner.
 Select “Graph Colors” to generate a graph.
 You can turn R or G or B or Average intensity on and off.
ADI also has a rectangle tool that can analyze a
mix of primary paints or dyes.
The relatively low RGB intensity levels in the rectangle are:
Red = 10.98%, Green = 10.35%, Blue = 9.11%
A histogram of colors in a rectangle reveals low
intensities of red, green and blue detected when blue,
red and yellow paints were mixed together.
Mixing primary paints produces a color that absorbs
more colors of light so it is called a subtractive process.
The ADI Resources Document provides examples of
how to use the Rectangle Tool.
The Rectangle Tool: This feature analyzes average intensities of
red, green, and blue light in the rectangle area of a photograph.
 Select the Rectangle Tool
 Press down using left click to draw a rectangle on the
photograph.
Create a color histogram of colors in the rectangle:
 Use the File Menu.
 Select “Graph Colors”.
 You can turn RGB or the Average Line on and off for the entire
photograph and/or for the area defined by the rectangle.
Different colors of a paint, dye or ink absorb
different colors of light.
 Blue paint absorbs principally red and green
wavelengths of light.
 Red paint absorbs principally blue and green
wavelengths of light.
 Yellow paint absorbs principally blue
wavelengths of light.
Mixing these 3 primary colors of paint absorbs three
primary colors of light that our eyes detect. The
cones of our eyes are not stimulated very much and
we perceive color as a black or muddy brown color.
Inexpensive spotlights can produce “fairly good”
complementary and white colors.
Note: Any 3 colors from three different regions of
the visible spectrum can be primary colors.
This is a photograph of a mix of red and green light.
Average Intensities along the line are: R = 69%, G = 57%, B = 38%
High quality lights in dark rooms result a much lower intensity of blue.
This graph of colors along the line across yellow light
illustrates that “red” and “green” sensors of a digital
camera responded to yellow light. The “blue” sensor did
not respond much to yellow light
An ADI rectangle tool can analyze the result of shining
inexpensive Red, Green and Blue spotlights onto a screen.
The relatively high intensities of RGB detected in the “white” light
are: Red = 62.14%, Green = 59.94%, Blue = 60.36%
An ADI histogram reveals fairly high intensities of red, green and
blue light in the white light produced during the demonstration.
Mixing primary colors of light produced a lighter color so
mixing colors of light is called an additive process.
Compare the graphs.
A mix of primary colors of
light
Additive
A mix of primary colors
of paint
Subtractive
You can use the Compare Colors Tab in ADI’s
Color Basics software experiment with colors of
pigments or light.
Some aspects of color theory results in
surprising results.
You can also play with color when word
using processing programs.
The Color Spaces tab in Color Basics indicates
the use of an intensity scale from 0 to 255.
255 + 1 = 256 = 28. 256 is a special number used in digital
computing because it is the maximum number represented
by an eight-digit binary number.
A Summary of Color Basics
Eyes and digital cameras detect light in the red, green
and blue ranges of the visible spectrum.
 Primary colors of light are different from primary
colors of paints or pigments.
 Mixing three primary colors of light is additive
producing a lighter color increases the intensities of
the primary colors detected by our eyes or a digital
camera.
 Mixing three primary colors of paints is subtractive
producing a darker color and reduces the intensities of
the primary colors detected by our eyes or a digital
camera.

Play with colors
Please take some time to explore
colors using Color Basics before
we discuss other features of ADI.