Recently I was
asked to lecture
at a college for
a course in advanced
professor asked that I
include color theory
in my lecture and at
first, I was a little overwhelmed
at the concept.
Color theory could fill an entire curriculum
in and of itself, yet I only had a scant
three hours to speak, and that was to be just
one of the topics.
I asked the professor for more detail on
what he’d like to have covered and why. He
told me that some of his students were having
trouble grasping the idea of colored light
and the way it interacts with colored sets
and costumes. Ah! OK! So I can cover an introduction
to additive and subtractive color
mixing and help clear up that concept a bit. Since that’s still fresh in my mind, it shall
be our adventure this month.
|Fig. 1: Additive color mixing, such as light, has different primaries. Subjective color mixing is what happens when you mix paint pigments together.
SEEING THE LIGHT
We cannot see light. This is a concept
that generally provokes quizzical stares
from my lecture attendees, but it’s a hard
fact of the physics of our world. We cannot
see the wavelengths (or particles) of light
traveling through space.
What we can see, is light reflecting or
refracting off of objects in our world. You
don’t see the light falling on the page as you
read this; you see the light reflecting off the
surface of the page to reach your eye. Some
people argue that they can see light beams in
the air, but we only see light beams because
that light is refracted through something in
the air; be that dust, moisture or smoke.
What our eyes see is the reflection of
light off of objects, and that light reflecting
off the object is altered by the object itself.
Every object in our world reflects a certain
amount of light, but it also absorbs a certain
amount. The colors you see are based on
wavelengths of light reflecting off of the object,
while others are absorbed.
We see a basketball as orange because
the pigments in the leather of that ball are
rejecting (reflecting) off certain yellow, orange
and red wavelengths of light while absorbing
green, blue, indigo and violet.
|Fig. 2: Red, green and blue light are mixed together. You can see the secondaries and white at the center.
The natural source of light in our world
is the sun. The sun, as an incandescent
source—that is light from heat—projects
light waves in all sizes so that light from the
sun contains all of the colors of the visible
spectrum: red, orange, yellow, green, blue,
indigo and violet (like Pluto, Indigo was
downgraded some time ago as not an “official”
part of the spectrum; but I still include
him for old time’s sake).
Under normal circumstances, all of these
wavelengths of light strike all the objects in
our world that are lit by the sun. Each object
absorbs some wavelengths and reflects others.
If we deprive that particular object of the
wavelengths of light that it rejects, we will significantly
alter the appearance of that object.
This is also a hard concept to grasp because
humans have wonderful color memory.
If I take a strawberry, which we all know
is red, and I put it in a dark room and light it with light that contains no red wavelengths,
the strawberry will appear blackish. Most
people look at that and say “it’s just dark.”
But the truth is the colors aren’t there to
reflect back to our eyes and cameras don’t
have this wonderful color memory. They
only record the truth.
SUBTRACTIVE AND ADDITIVE
There are two different physics of color
mixing: subtractive and additive, (see Fig. 1).
Subtractive color mixing is what happens
when you mix paint pigments together. For
anyone who ever took art classes as a kid,
you were taught the primary colors were
red, yellow and blue. I’m here to tell you
that’s an outright lie. I
think they teach kids this
because magenta and
cyan are difficult words
to grasp at an early age.
The pigment primaries
are magenta (not red),
cyan (not blue) and yellow
(they got that one
|Fig. 3: Subtractive color mixing and the results using yellow,
magenta and cyan filters.
When you mix pigment
every addition of a new
color darkens your result.
In subtractive mixing,
every addition of a
new color brings the result
closer to black. The
combination of all colors is black and the
absence of color is white.
Additive color mixing, such as light, has
different primaries. We deal with red, green
and blue. If you keep in mind that every
addition of a light source makes the result
brighter, it’s easier to grasp that as you add
colors in additive mixing, you get closer to
white. White light is the combination of all
colors and black is the absence of light.
The two physics of color work together.
When you mix pigment primaries (also
called secondaries), you get the lighting primary
colors. Mix cyan and magenta
together to get blue. Mix
yellow and cyan together to get
green. Mix yellow and magenta
together to get red. When you
mix enough equal parts of yellow,
cyan and magenta, you get
Likewise, if you’re using the
primary colors of light, you can
mix red and green to get yellow
(remember in additive, the
result is brighter than the two
colors you’re mixing); you can
mix green and blue together to
get cyan and you can mix blue
and red together to get magenta.
When you combine red, green
and blue together, you get white.
Figs. 2 and 3 are two actual
photographs I took looking at
real-world physics of color in
action. Fig. 2 uses red, green and
blue light mixed together and
you can see the secondaries
and a close approximation of white at the
center. My sources weren’t the most pure
sources so the color mix isn’t perfect, but
it’s definitely a real-world example.
Fig. 3 shows subtractive color mixing
using colored gels. Gels are subtractive because
they stop certain wavelengths of light
from passing through. In essence, they absorb
those colors and allow others to pass
through. So we start with white light (red,
green and blue) and pass that through a yellow
filter. The yellow stops the blue and lets
red and green pass through. The result is
yellow light (red and green light combined
|Fig. 4: In example A, the strawberry is displayed using a white light. In B, it is displayed using a cyan filter, which stops the red from passing through.
Note that the intensity of the light is reduced because we’re filtering out some
of the wavelengths, so we’re down to 25
percent original intensity now. When we
put a magenta filter in front of that, it stops
the green light, but allows the red to pass
Now we only have red light—and it’s 7
percent of the original intensity because
we’ve filtered out all the other wavelengths.
Finally we put a cyan filter in the path of
the red light and the result is zero-percent
intensity. The cyan filter doesn’t allow the
red to pass through, so we have no light on
the other side.
Where this intertwines is when we realize
that we only see objects in our world
as their colors because they are reflecting
those wavelengths back to our eyes. So if
we go back to the example of the strawberry
and we light it with white light,
we’ll see that beautiful red, (see Fig. 4), but
if we put a cyan filter in front of the light
source that stops red light from reaching
the strawberry, it will no longer be receiving
the red to reflect it back and will appear
nearly black. (There are other wavelengths
of light mixed in with the red, so
not pure black.)
You have to keep the principles of both
additive and subtractive color mixing in
mind when you’re lighting a set. The colors
of the walls, set, props, products, etc., are all
biased by the colors (and integrity of color)
of your light sources.
One student at the school had a set that
was painted all brown and they wanted a
moonlight feel with blue light and were
confused when the walls became black in
their image. The walls were black because
the blue light didn’t contain the red and
yellow that the walls wanted to reflect, so
they went black.
This whole topic is further complicated
by white balance and picking your white
point, which biases the way the camera
sees colors even further, but that’s a subject
for another day.
Jay Holben is the technical editor of
Digital Video and a contributor to Government
Video. He is also the author of
the book “A Shot in the Dark: A Crative
DIY Guide to Digital Video Lighting on
(Almost) No Budget.”