Transcript JrowanITEC2110-01&04Oct12ColorPart2.ppt

Digital Media
Dr. Jim Rowan
ITEC 2110
Color Part 2
Roll call
Barton, Paul H.
Bois, Lauren C.
Bonds, Allison E.
Duncan, Jarred T.
Lawson, Joseph I.
Mulongo, Julio B.
Pennison, Heather L.
Reilly, Daniel J.
Sanchez-Casas, Jon F.
Simson, Davis
Sinnock, Grant A.
Swaim, Mark S.
Tran, Dung Q.
Vyas, Anand A.
Woldeyohannes,
Tesfamichael
Roll call
Jones, Crystal L.
Marsh, Kerreen A.
Thompson, Daniel G.
Tran, Christopher V.
Color Models other than RGB
• CMYK
–
–
–
–
cyan
magenta
yellow
key (black)
• HSV, HSB, HSL
– Hue
– Saturation
– value. brightness, lightness
• First, CMYK ==>
CMYK
• Colored light shining on a white surface
• One red light, one blue light and one
green light
• Arranged to overlap...
• Creating Cyan, Magenta and Yellow: the
complementary colors
g
y
r
w c
m
b
CMYK
Yellow = Red + Green
Yellow = White - Blue
g
y
r
w c
m
b
Cyan = Green + Blue
Cyan = White - Red
Magenta = Red + Blue
Magenta = White - Green
CMYK is an Additive model (like RGB) and
appropriate for use with light
CMYK also provides the Subtractive model that
is appropriate for use with ink and paint... things
that absorb light
removes green
CMYK
removes green
white light
white light
leaving
magenta
light
leaving removes red
magenta
removes red
light
white light
leaving
blue light
magenta ink
white paper
cyan ink
white paper
leaving
blue
light
CMYK & Ink
• You can make black by printing the all three
color inks but...
– it isn’t a very good black...
•
•
•
•
•
Cyan, Magenta and Yellow inks aren’t perfect
They are chemical compounds
Some Red is reflected by cyan ink
Some Blue is reflected by yellow ink
Some Green is reflected by magenta ink
– takes a long time to dry
• Many printing processes are supplemented
by black ink
The HSV model
• RGB and CMYK make sense theoretically
(based on cones in the eye) but...
• They don’t correspond to the way we
experience color in the real world
• You don’t look at a patch of Cyan color and
think about the mixture of green and blue light
in it
• You probably relate to Cyan to other blues
you know (hue), how pale it is (saturation)
and its brightness (intensity-V)
HSV
• Three dimensions H S V
• Hue - is the dominant frequency
– expressed as degrees from red
• Saturation - how pale the hue is
– adding white to paint reduces the saturation
• V - The color’s value, brightness or
lightness
– adding black to paint reduces the brightness
Historical Trivia and Color
• Consider the B&W tv and the Color tv
• B&W just needs intensity changes to make white-gray-black
– intensity varies as the electron beam is drawn across the screen
• Color is RGB+Intensity for each
– could transmit each color with its intensity and it would work for color tv but
– can’t use the same signal model for color because the B&W tv’s wouldn’t work
– Solution: Transmit the necessary color information during the retrace.
– Color is transmitted as luminance and two colors
– B&W tv’s simply ignore it because the beam is off
Channels and color images
• Each of the RGB can be shown as a
grey scale image
• Each of the RGB is stored in its own
array
• Each can be manipulated individually
RGB
Channels
RGB RGB RGB
RGB RGB RGB
R
R
R
RGB RGB RGB
R
GR
GR
G
R
GR
BGR
B
G
B
G
BG
B
G
B
B
B
B
• Allows the use of the brightness
and contrast of each individual
color to be manipulated using
levels and curves
• Allows a very fine level of
control
• Very time consuming
• Color balance, hue and
saturation adjustments on the
whole image is a shortcut
Color consistency?
• Different devices use different phosphors
• Physical devices are not usually linear
– Red, Green and Blue phosphors each react
differently and
– They do not react linearly... this means
• 10 times as much excitation will not produce 10 times as
much emitted light
• In the end, it is all a compromise
• Phosphors and excitation circuitry age
Questions?