AOH :: COLOR1.TXT Color theory
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January 14, 1991

COLOR1.ASC
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Color Theory Basics

Color theory explains  what  color  is, how the human eye sees color
and the methods used to create all the colors in the color spectrum.

To begin learning about color, we  must  start  with light.  We must
have light to  see  things.   Light  shines  on  an  object  and  is
reflected back to  our  eyes, allowing us to see the objects as they
are.  Objects ONLY REFLECT THE COLORS THEY ARE MADE UP OF, and it is
these colors that are received by the eye.

When we refer to light, we mean white light.  White light is made up
of EQUAL AMOUNTS of RED, GREEN and  BLUE light.  If we were to shine
three PURE beams of red, green and blue light together  and slightly
overlap them, we  can see that where the three overlap, the color is
white.

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PRIMARY COLORS

RED, GREEN and BLUE are referred to  as the PRIMARY COLORS of light.
Because we ADD them together to create color, we call  them ADDITIVE
COLORS.

Where two of the beams overlap, we actually create a third different
color.

Where we overlap  the BLUE and GREEN, we create a new color known as
CYAN.  CYAN is a combination of blue light and green light.

Where BLUE and RED overlap, we get  a color called MAGENTA.  MAGENTA
is a combination of blue and red light.

Where the RED and GREEN beams overlap, we create YELLOW!   Remember,
these are pure  beams  of  colored  light.   YELLOW  is  created  by
combining equal amounts of red and green light.

CYAN, MAGENTA and YELLOW are called  the SUBTRACTIVE COLORS, because
we create color by using them to SUBTRACT COLOR from WHITE LIGHT.

To help us keep these colors in proper perspective  with each other,
we shall refer to the color triangle below.  The colors at the

Page 1

POINTS of the triangle are the three additive colors, RED, GREEN and
BLUE.

The three colors  along  along  the  SIDE  of  the  triangle are the
SUBTRACTIVE COLORS, MAGENTA,  YELLOW,  and  CYAN.   The  subtractive
colors are placed between the two additives that  they  are  made up
of.  For example,  the  magenta  is between the red and blue because
red and blue make magenta.

RED
@
*   *
(R + B = M)    MAGENTA<<<<@       @>>>>YELLOW   (R + G = Y)
*           *
*               *
BLUE<<<<@ * * * * @ * * * * @>>>>GREEN
CYAN
(B + G = C)

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Up until now, we have been combining  two  primary colors at a time.
What would happen if we add together one SUBTRACTIVE  color  and one
ADDITIVE color of light?

Red    +   Cyan    = White Light
(green +   blue)

Blue   +   Yellow  = White Light
(red   +   green)

Green  +   Magenta = White Light
(red   +   blue)

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COMPLIMENTARY PAIRS

Complimentary pairs are  the  combination  of  one  additive and one
subtractive color together to recreate white light.

If you keep in mind that the subtractive  colors  are made up of two
additive colors, by adding the remaining additive color we get white
light again.

Blue is complementary to Yellow
Green is complementary to Magenta
Red is complementary to Cyan

In most of the situations where we find color, it has  been  derived
through the subtractive process.  Paintings, photographic prints and
color negative film  all  rely  on  the SUBTRACTIVE colors to create
color.

The most common application of the  additive  colors  is television.
It uses a combination of red, green and blue dots to  create a color
picture on the screen.

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FILTERS

A filter is a device that will block out certain amounts or kinds of
light.

A NEUTRAL FILTER  ABSORBS  EQUAL  AMOUNTS of the red, green and blue
that make up  the white light.  The  transmitted  colors,  or  those
allowed to pass, are the same as the original colors,  just  not  as
intense.

NEUTRAL FILTER

WHITE       RED>>>>>>>>>>>>>NNN>>>>>>>>>>RED        all
LIGHT RAYS  GREEN>>>>>>>>>>>NNN>>>>>>>>>>GREEN     colors
BLUE>>>>>>>>>>>>NNN>>>>>>>>>>BLUE       pass

Neutral shades of  sunglasses  produce  this  effect of reducing the
intensity of the colors without changing the colors themselves.

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In the photographic process, subtractive  colors  are used to create
color.  Color filters are used to SELECTIVELY choose  what  color we
want to see while eliminating other unwanted colors from light.  The
use of filters  is  basic  to  the understanding of how photographic
film and paper are designed to reproduced the colors of the subject.

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If a RED filter is placed in front  of  a  beam  of white light, you
will see the  color  RED.   Red  light  is allowed  to  pass  or  be
transmitted through while  the  green  and blue light are blocked or
absorbed.

RED FILTER

WHITE       RED>>>>>>>>>>>>>RRR>>>>>>>>>>RED    only RED
LIGHT RAYS  GREEN>>>>>>>>>>>RRR                 passes through
BLUE>>>>>>>>>>>>RRR

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If a GREEN filter is placed in front  of  a beam of white light, you
will see the color GREEN.  Green light is transmitted  through while
the red and blue light is absorbed.

GREEN FILTER

WHITE       RED>>>>>>>>>>>>>GGG                 only GREEN
LIGHT RAYS  GREEN>>>>>>>>>>>GGG>>>>>>>>>>GREEN  passes through
BLUE>>>>>>>>>>>>GGG

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If a BLUE  filter  is  placed in front of a beam of white light, you
will see the color BLUE.  Blue light  is  transmitted  through while
the red and green light are absorbed.

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BLUE FILTER

WHITE       RED>>>>>>>>>>>>>BBB                only BLUE
LIGHT RAYS  GREEN>>>>>>>>>>>BBB                passes through
BLUE>>>>>>>>>>>>BBB>>>>>>>>>>BLUE

Remember that ANY filter TRANSMITS ITS OWN COLOR.
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If you place  a  CYAN  filter in front of a beam of white light, you
will find the RED light is ABSORBED  while  the BLUE and GREEN light
are TRANSMITTED.  This is because CYAN is MADE UP of  BLUE and GREEN
and a CYAN filter TRANSMITS its own color.

CYAN FILTER
(full strength)
WHITE       RED>>>>>>>>>>>>>CCC                 only GREEN & BLUE
LIGHT RAYS  GREEN>>>>>>>>>>>CCC>>>>>>>>>>GREEN  passes through
BLUE>>>>>>>>>>>>CCC>>>>>>>>>>BLUE
(absorbs RED)

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If you place a MAGENTA filter in front of a beam of white light, you
will find the  GREEN  light is ABSORBED while the RED and BLUE light
are TRANSMITTED.  This is because  MAGENTA  is  a combination of RED
and BLUE.

MAGENTA FILTER
(full strength)
WHITE       RED>>>>>>>>>>>>>MMM>>>>>>>>>>RED    only RED & BLUE
LIGHT RAYS  GREEN>>>>>>>>>>>MMM                 passes through
BLUE>>>>>>>>>>>>MMM>>>>>>>>>>BLUE
(absorbs GREEN)

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If you place a YELLOW filter in front of a beam of  white light, you
will find the  BLUE  light is ABSORBED while the RED and GREEN light
are TRANSMITTED.  This is because YELLOW is a combination of RED and
GREEN.

YELLOW FILTER
(full strength)
WHITE       RED>>>>>>>>>>>>>YYY>>>>>>>>>>RED    only RED & GREEN
LIGHT RAYS  GREEN>>>>>>>>>>>YYY>>>>>>>>>>GREEN  passes through
BLUE>>>>>>>>>>>>YYY
(absorbs BLUE)

Each subtractive filter   ABSORBS   ONE   COLOR   of   light   while
TRANSMITTING the other TWO COLORS.

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Often, it is  necessary to use more than one filter  at  a  time  to
obtain the desired  results  of blocking out ALL BUT ONE COLOR.  The
following diagrams illustrate how  a  set of two SUBTRACTIVE filters
work together to filter out ALL BUT ONE COLOR from  a  beam of white
light.

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MAGENTA       CYAN
FILTER       FILTER
WHITE       RED>>>>>>>MMM>>>>>>>>>CCC           only BLUE
LIGHT RAYS  GREEN>>>>>MMM         CCC           passes through
BLUE>>>>>>MMM>>>>>>>>>CCC>>>>>BLUE

If a MAGENTA  and  CYAN  filter  are  used together, you can see the
MAGENTA filter ABSORBS the GREEN and TRANSMITS the RED and BLUE.

Then the CYAN filter ABSORBS the  RED  and  allows  the  BLUE  to be
TRANSMITTED.

We know from our triangle that CYAN is made from GREEN and BLUE, but
since the GREEN was ABSORBED earlier by the MAGENTA filter, there is
NO GREEN for  the CYAN filter to be TRANSMITTED, resulting  in  only
the remaining BLUE color.

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If CYAN and  YELLOW  are  used together, you can see the CYAN filter
ABSORBS the RED and allows the BLUE  and  GREEN  to  be TRANSMITTED.
Then the YELLOW filter absorbs the BLUE and allows  the  GREEN to be
TRANSMITTED.

From our triangle  we  see  YELLOW  is  made from RED and GREEN, but
since the RED was ABSORBED earlier  by  the CYAN filter, there is no
RED for the  YELLOW  filter  to  TRANSMIT,  resulting  in  only  the
remaining GREEN color.

CYAN        YELLOW
FILTER       FILTER
WHITE       RED>>>>>>>CCC         YYY           only GREEN
LIGHT RAYS  GREEN>>>>>CCC>>>>>>>>>YYY>>>>>GREEN passes through
BLUE>>>>>>CCC>>>>>>>>>YYY

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If you use  the  MAGENTA  and  YELLOW  filters together, you see the
MAGENTA filter ABSORBS the GREEN and  allows  the RED and BLUE to be
TRANSMITTED.  The YELLOW filter then ABSORBS the BLUE  and TRANSMITS
the RED.

From the triangle,  we  can  see  that  YELLOW  is made from RED and
GREEN, but since  the MAGENTA filter  ABSORBED  the  GREEN  earlier,
there is no GREEN, leaving only the remaining RED color.

MAGENTA      YELLOW
FILTER       FILTER
WHITE       RED>>>>>>>MMM>>>>>>>>>YYY>>>>>RED   only RED
LIGHT RAYS  GREEN>>>>>MMM         YYY           passes through
BLUE>>>>>>MMM>>>>>>>>>YYY

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With the YELLOW  filter  first,  we  see the BLUE  is  ABSORBED  and
TRANSMITS the RED  and  GREEN.   When  the  RED  and GREEN reach the
MAGENTA filter, the  GREEN  is  ABSORBED   and   the  RED  light  is
transmitted.

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From the triangle,  we  know  MAGENTA is made from RED and BLUE, but
since the YELLOW filter ABSORBED  the  BLUE  earlier,  only  the RED
component remained to be transmitted.

YELLOW       MAGENTA
FILTER       FILTER
WHITE       RED>>>>>>>YYY>>>>>>>>>MMM>>>>>RED   only RED
LIGHT RAYS  GREEN>>>>>YYY>>>>>>>>>MMM           passes through
BLUE>>>>>>YYY         MMM

As this comparison showed, it really isn't important  in which order
the two filters  are  used,  the single color that remains is ALWAYS
the same.  Referring to the color  triangle will help keep the color
relationships straight for you.

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Now, what would happen if you put ALL THREE SUBTRACTIVE  filters  in
front of a light beam?

As you can see, the combination of all THREE FILTERS TOTALLY ABSORBS
ALL of the  light  and NO COLORS are allowed to pass through.  Equal
intensity filters of CYAN, MAGENTA and YELLOW make up what is called
a NEUTRAL FILTER.  This means that  the  color of light seen will be
NEUTRAL or HAVE NO COLOR.

MAGENTA  CYAN    YELLOW
FILTER   FILTER  FILTER
WHITE       RED>>>>>MMM>>>>>>>CCC     YYY         NO LIGHT
LIGHT RAYS  GREEN>>>MMM       CCC     YYY         passes through
BLUE>>>>MMM>>>>>>>CCC>>>>>YYY

Up to this point, we have been talking about FULL STRENGTH  filters.
In other words,  a  full  strength  CYAN filter would ABSORB all RED
light and TRANSMIT GREEN and BLUE light.

It is possible to VARY THE INTENSITY  of  the  filter  so  that SOME
amount of colored light will be ABSORBED.  This means  that  a LOWER
INTENSITY CYAN filter  would  ABSORB  some RED and TRANSMIT some RED
light alown WITH the GREEN and BLUE light.

CYAN FILTER
WHITE       RED>>>>>>>>>>>>>CCC> > > > > RED     only some RED
LIGHT RAYS  GREEN>>>>>>>>>>>CCC>>>>>>>>>>GREEN   FULL GREEN
BLUE>>>>>>>>>>>>CCC>>>>>>>>>>BLUE    FULL BLUE

If we CHANGE THE INTENSITY OF A NEUTRAL  FILTER,  we  will  vary the
intensity of RED,  GREEN,  and  BLUE light TRANSMITTED.   Since  the
filter is NEUTRAL,  the  RED, GREEN, and BLUE light will be in EQUAL
AMOUNTS causing the light to APPEAR NEUTRAL in color.

The table below will serve as a reference  to  the three SUBTRACTIVE
colors that are  most  commonly used as filters in  color  film  and
paper construction.  Always keep in mind the COMPLEMENTARY PAIRS.

Page 6

Filter Color        Light Transmitted      Light Absorbed

CYAN                GREEN & BLUE            RED
(CYAN)

MAGENTA             RED & BLUE              GREEN
(MAGENTA)

YELLOW              RED & GREEN             BLUE
(YELLOW)

It is important  to mention here that so far we have been discussing
filters that are  ideal,  or  perfect,   meaning  they  absorbe  the
complimentary color completely.

In reality, this is not so.  The filters are NOT PERFECT, so a small
amount of the complimentary color does get transmitted,  and a small
amount of the  other two colors are absorbed.  However, it should be
noted that the change in intensity will not create a problem.

One must remember that we are dealing with PURE colors.

Shades of pure and complimentary  colors  arise  from  the action of
imperfect filtering.  Therefore, color correction/compensation  must
ultimately be decided by the viewer.

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A REVIEW

WHITE LIGHT is  comprised  of  EQUAL  AMOUNTS OF RED, GREEN and BLUE
light added together.  Thus, red,  green  and  blue  are  called the
PRIMARY COLORS of light.

We can also create color by ABSORBING RED, GREEN or  BLUE from white
light using SUBTRACTIVE COLOR filters, CYAN, MAGENTA, and YELLOW.

ANY FILTER TRANSMITS ITS OWN COLOR AND
ABSORBS ITS COMPLIMENTARY COLOR.

CYAN absorbs RED light and allows BLUE and GREEN light to pass.
MAGENTA absorbs GREEN light and allows BLUE and RED light to pass.
YELLOW absorbs BLUE light and allows RED and GREEN to pass.

When two or  more  filters  are  used together, it doesn't matter in
which order they are placed, the result will be the same.

When all three subtractive filters  of equal intensity are combined,
the result is a NEUTRAL FILTER.

When placed in front of a beam of white light, the light transmitted
will be NEUTRAL in color and its BRILLIANCE depends on the intensity
of the filter.

Filters are not  perfect in design, so a very small  amount  of  the
color of light  that  should  be absorbed actually does pass through
the filter.

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If you  have comments or other information relating to such topics
as  this paper covers,  please   upload to KeelyNet or send to the
Vangard  Sciences  address  as  listed  on the  first  page.
Thank you for your consideration, interest and support.

Jerry W. Decker.........Ron Barker...........Chuck Henderson
Vangard Sciences/KeelyNet

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If we can be of service, you may contact
Jerry at (214) 324-8741 or Ron at (214) 242-9346
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