Food Color What is color

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             What is color?

• The subject of color is complex because it
  includes many factors.
• Color is the physics of light.

• Color is the chemistry and physics of the
  materials that light "colors."
            What is color?
• Color is the human response
to light

• Color is the human judgment of the color
           What is color?
• In themselves each of the components are
  made up of a complicated series of factors.
  Together they create the human sensation we
  call color.
Instrumental Measurement of
           • To create a computerized
             device that will measure and
             describe color like we see and
             judge color; we need to
             simulate the system that
             creates the human color
           • Color instruments need a
             controlled light source that we
             can define mathematically
Instrumental Measurements
          • The colored materials to be
            measured must be presented to
            the instrument in a uniform

          • Devices are created in the
            instrument that senses the
            light in the human visual range
            that is reflected or
            transmitted from the materials
            to be measured.
What is a Color Computer

            • Computer programs
              relate the data from the
              color instrument to the
              human response to color
              using mathematical
              simulations of light,
              human vision and
            • Thus you can see that the
              color computer is as
              complex as the human
              color response
Color begins with light. What do we know
about light and color?
• Light travels at the rate 300,000 Km/s
  in the vacuum of space and slows as the
  material it passes through becomes
• Light can pass through clear gasses,
  liquids, solids and a vacuum. When you
  change the density of the media, you
  slow the speed and bend the light
  waves in a predictable manner. This is
  called the refractive index of a
Light can be measured in wavelengths in the
spectrum of electromagnetic radiant energy

              • Wavelengths of light between 400nm
                and 700nm are the range of light
                energy where 99% of human color
                response occurs (called the visual
                range) and is commonly referred to
                as the visual spectrum.
              • Light can be selectively scattered
                and absorbed by some materials in
                gasses, liquids and solids. As a group,
                these materials are called colorants.

• Each wavelength area in the visual spectrum creates
  one pure color sensation.
• The individual wavelengths in the visual range are
  called monochromatic light. Objects illuminated with
  monochromatic light can only exhibit that single color.
For example, red, orange, yellow, green,
blue, violet are primary, monochromatic
light colors.
When all wavelengths of light in the visual
spectrum, between 400-700nm, are mixed at
equal energy, we see the "perfect" white light.
When all wavelengths in the visual spectrum
between 400-700nm are not present, we have
the "perfect" black.
• If you have only one
  wavelength of light in the
  visual spectrum, you will only
  see one color. Adding other
  wavelengths changes the
  color as the light mixes.
• Light sources, that is "real"
  lights, such as sunlight,
  incandescent, tungsten, and
  fluorescent, have different
  balances of wavelengths of

               • The eye is the window to
                 the color experience.
                 Whether the light comes
                 directly from a light source
                 and is subject to additive
                 light mixing or is reflected
                 by or transmitted through a
                 material, it is the
                 brightness and balance of
                 the light energy that
                 creates the color stimulus

              • Light enters the eye, passing
                through the cornea, aqueous
                humor, the lens, through the
                vitreous humor, and falls on
                the light-sensitive retina.

              • Three types of cone cells in
                the retina respond to the
                color balance of the light
                stimulus. There are red cone
                cell responders, green cone
                cell responders and blue cone
                cell responders.

                        • Since there are more than 7
                          million cone cells in the
                          retina, we can see many
                          different colors in one scene
                          at the same time. Rod cells
                          relate to the brightness of
                          light (white to black). There
                          are over 17 million rod cells

• Note that each of the cone cell responses which are
  diagrammed as the R, G, B curves covers a broad band
  of color space, that the responses overlap and have
  areas where they are more sensitive than other areas
  and that they are at a different level of response
  We see all colors in our vision range at the
  same time. Sometimes the relationship
  between colors that surround each other
  confuses our color vision.

• Look at the color in the center of each display. It
  looks different because the surround color influences
  the way you see the color.
  How can the human response be programmed in a
  computer?             • Experiments were done in
                          the 1920's using observers
                          working with devices that
                          allowed the observer to mix
                          red, green, and blue filtered
                          light to match target colors
                          created by another filtered

• The data was gathered after thousands of tests, and
  the results were calculated to define the human red,
  green, and blue response
                        • Based on the data,
                          calculations were developed to
                          simulate the average color
                          matching characteristics of
                          people having normal vision.
                          (The R, G, B data was
                          previously discussed as the
                          retinal response.) The retinal
                          response data is transformed
                          to X,Y,Z as shown in the next

• Human data is used in all Color Computer programs as
  the basic information to calculate how the human sees
  color and is often defined in color computer programs
  as the Standard Observer (2- or 10-degree)
                         • If we are interested in how
                           a color of an object looks,
                           we need to know what type
                           of lighting with which we will
                           be looking at the object.

                         • In the color computer, we
                           have stored the illuminant
                           mathematical tables for the
                           light sources in which we are

• We select the illuminant of choice in our program, in
  this case, Average Daylight "D65."
We now measure the object
color in which we are
interested with a color
instrument. The data is
then used in the color
                     In the color computer, the
                     color software relates the
                     illuminant data, which is the
                     relative energy of the light
                     source, and multiplies the color
                     measurement data and the
                     color matching functions to
                     yield three curves.

These curves are the tristimulus values X, Y, Z. This
is the basis for the mathematics in the color
computer that tells us how a color will look based on
a color measurement.
• The vision sensations that
  are sent to the brain create
  the three dimensions of
  color judgment response
  that is often referred to as
  three-dimensional color

• The dimensions are light to
  dark (L); reddish to greenish
  (a); yellowish to bluish (b).
              • brightness: the attribute
IMPORTANT       of a visual sensation
DESCRIPTORS     according to which a
                sample appears to exhibit
                more or less lightness.
              • hue: the color of a sample
                relating to primary colors
                such as red, yellow, green,
                blue or its absolute color.
                This becomes hard to
                define in terms of complex
                mixtures of color such as
                browns or purple. In terms
                of color difference, any
                color can change in hue and
                be defined in these terms.
              • Chroma: the colorfulness
IMPORTANT       of a sample relating the
DESCRIPTORS     saturation relative of the
                range from a pure hue to a
                neutral color having no hue
                (lying along the gray scale
                from white to black.
• Experiments were done that were set up to test how
  an observer would judge just barely visual color

                             The data from this
                             experiment showed that
                             we see color more
                             critically when a color is
                             lighter than darker, and
                             we judge color
                             difference more
                             critically in the blue
                             range than in the red or
                             green areas of color
                           The mathematics
                           resulting from these
        Lighter            experiments is
                           called color
                           calculations. They
Green                      can predict that one
                           color will appear
                           lighter or darker,
                           redder or greener,
                           yellower or bluer
                           than another. We
                           can also calculate if
                           the color is shifting
Blue               Red     in lightness,
                           changing in hue, or
                           changing in chroma
            Color Space
              L= lightness (white= 100)

                       b= (+) yellow

a= (-)
green                                  a= (+) red

         b= (-) blue

              L= lightness (black=0)
We express this data in the three dimensions of
human color response. The mathematics is expressed
as L, a, b factors defined as either Hunter L,a,b or
CIE L,a,b:

L = Lightness
(black= 0 and white = 100)
a = +a redness to greenness -a
b = +b yellowness to blueness -b

(greener or less red the "a" factor becomes smaller)
      (redder or less green the "a" factor is larger)
(yellower or less blue, the "b" factor is larger)
bluer or less yellow, the "b" factor becomes smaller
             LAB Color Space

•   Common Systems
•   1. CIE XYZ
•   2. CIE L*, a*, b*
•   3. L a b Hunter
•   L= lightness (black=0, white= 100)
•   a= (+) red, (-) green
•   b= (+) yellow, (-) blue
How do Lab values describe color?
• LIGHTNESS: Bright colors, dark colors
• L= lightness (black=0, white= 100)

• CHROMA: Saturation of a particular color,
  vivid to dull
• Chroma*= a*2 + b*2

• HUE: (angle). Color or predominant
  wavelength (true reading). Numeric
  description of the color Red, yellow, blue.
• Hue*= tan-1 (b*/a*)
         Example of a Calculation

•   L*= 45.81
•   a*= 33.99
•   b*=58.55
•   Hue*= tan-1 (58.55/33.99) = 59.86
•   Chroma = (33.99)2 + (58.55)2= 67.70

•   HUE (angle )
•   a>0 y b=0 therefore, Hue= 
•   a<0 y b>=0 therefore, Hue= 180 +
•   a<0 y b<0 therefore, Hue= 180 +
•   a>0 y b<0 therefore, Hue= 360 +
• Green-yellow      L*= 76 a*=-2.0    b*=56
• 92
• vivid orange-yellow L*= 74 a*=2.0   b*=56
• Hue??
• 88
• Chroma?? 56
• dull orange yellow L*= 63 a*=1.2    b*=34
• Hue??
• 88
• Chroma?? 34

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