Digital Media

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

2. Color Models other than RGB • CMYK • cyan • magenta • yellow • key (black) • HSV, HSB, HSL • Hue • Saturation • value. brightness, lightness • First, CMYK ==>

3. g y r w c m b 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

4. g y r w c m b CMYK Yellow = Red + Green Yellow = White - Blue 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

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

6. 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

7. 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)

8. 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

9. 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

10. 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

11. RGB Channels • 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

12. 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

13. Questions?