Transcript 7 jrowanSpring2013ColorPart2.pptx

Digital Media
Lecture 7: Color part 2
Georgia Gwinnett College
School of Science and Technology
Dr. Jim Rowan
Refer to Supplemental text:

You have a blue ball and walk into a
room lit with a red light. What color is
the ball while in the room?
r
y
g
w c
m
b
Color Models other than RGB

CMYK
–
–
–
–

cyan
magenta
yellow
key (black)
HSV, HSB, HSL
– Hue
– Saturation
– value. brightness, lightness
r

y
g
w c
m
b
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 and…
 White

Yellow = Red + Green
Yellow = White - Blue
r
Magenta = Red + Blue
Magenta = White - Green
y
g
w c
m
b
Cyan = Green + Blue
Cyan = White - Red
White = Red + Green + Blue
This color model can be used as an Additive model
appropriate for use with light
This color model can also be used as a Subtractive model
appropriate for use with ink and paint...
things that absorb light
leaving
magenta
light
removes green
white
light
white
light
removes
green
leaving
magenta
light
removes red
removes red
white
light
leaving
blue light
magenta ink
white paper
cyan ink
white paper
leaving
cyan
light
CMYK model
Cyan
 Magenta
 Yellow
 Key (black)

– While you should be able to make black by
mixing Cyan, Magenta and Yellow…
– Paint (and ink) is not perfect
Subtractive model
 Used by the printing industry

HSV model


Another way of looking at color
Hue
– The color described as degrees from red

Saturation
– How pale the color is
– Think of it as adding white to the color

Brightness
– How intense the color is
– Thinks of it as adding black to the color
Adjusting the Hue
Adjusting the Hue
Adjusting the Hue
Adjusting the Hue
Adjusting the Saturation
Adjusting the Value
Full-On Red in RGB model
Full-On Green in RGB model
Full-On Blue in RGB model
The transition from
B&W to 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
RGB
RGB RGB RGB
Channels
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
Channels
Red
Green
http://en.wikipedia.org/wiki/Channel_(digital_image)
Blue