1. Dr. Jim Rowan ITEC 2110 Color Part 2
Digital Media
Dr. Jim Rowan
ITEC 2110
Color Part 2

2. w g r b c y m

3. Question
You have a blue ball and walk into a room lit with a red light. What color is the ball while in the room?
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4. Color Models other than RGB
CMYK
cyan
magenta
yellow
key (black)
HSV, HSB, HSL
Hue
Saturation
value. brightness, lightness
First, CMYK ==>

5. 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 w g r b c y m

6. CMYK Yellow = Red + Green Yellow = White - Blue g y r w c
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

7. CMYK removes green magenta leaving light removes red removes red
white light
white light
magenta
leaving
light
white light
leaving
blue light
blue
leaving
light
magenta ink
white paper
cyan ink
white paper

8. 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

9. 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)

10. 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

11. Adjusting the Hue

12. Adjusting the Hue

13. Adjusting the Hue

14. Adjusting the Hue

15. Adjusting the Saturation

16. Adjusting the Value

17. Full-On Red in RGB model

18. Full-On Green in RGB model

19. Full-On Blue in RGB model

20. 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

21. Channels and color images
Each of the R and the G and the B can be shown as a grey scale image
Think of each as being stored in its own array
That way, each can be manipulated individually

22. RGB
Channels
RGB R G 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

24. Color consistency? Probably not.
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 age and change
Excitation circuitry age and change

25. Questions?