Color is a sensation produced by the human visual system. The two most common color models are RGB, used for computer displays, and CMYK, used for printing. RGB is an additive model that uses combinations of red, green, and blue light to produce colors. CMYK is a subtractive model that uses combinations of cyan, magenta, yellow, and black inks to produce colors. Both models represent colors using three numeric values corresponding to the intensities of the primary colors.

1. Color
BY HASHMI SAFWAN

2. What is color ?
 Color is a sensation produced by the human eye and nervous system.
 It is useful to represent a color by a set of exactly three numbers.

3. Color is Human Sensation
 Cone and rod receptors in the retina
 Rod receptor is mostly for luminance perception
 3 different types of cone receptors in the fovea of retina, responsible for
color representation. Each type is sensitive to different wavelengths

4. Color model
 A color model is an orderly system for creating a whole range of colors from a small set
of primary colors.

5. Types of Color model
 Subtractive Color
 Additive Color
 Additive color models use light to display color
 subtractive models use printing inks.

6. The Two Most Common Color Models
 RGB model
 For computer
 CMYK model
 For printing
 YCbCr model

7. RGB Color Model:
 Additive color model.
 For computer displays.
 Uses light to display color.
 Colors result from transmitted light.
 Red + Green + Blue = White.

8.  The RGB Color Model
 If R,G, and B are represented with 8 bits (24-bit RGB
 image), the total number of colors is (28 )3=16,777,216

9. CMYK Color Model
 Subtractive color model.
 For printed material.
 Uses ink to display color.
 Colors result from reflected light.
 Cyan + Magenta + Yellow = Black
 Used internally in color printers
 Complementary to RGB:
 C=1-R
 M=1-G
 Y=1-B

10. Color Models
 the color model RGB is used in hardware applications like PC monitors, cameras and scanners, the CMY
color model is used in color printers,
 Each color can be a point in the RGB color model cube. Red, green and blue are known as the primary
colors. These colors can be added to produce secondary colors which are:
 magenta = red + blue
 cyan = green +blue
 yellow = red + green
 Other possible combinations:
 white = blue (primary) + yellow (secondary)
 white = green (primary) + magenta (secondary)
 white = red (primary) + cyan (secondary)

11. Additive vs. Subtractive Color Models
 Since additive color models display color as a result of light being transmitted (added) the total absence of
light would be perceived as black. Subtractive color models display color as a result of light being absorbed
(subtracted) by the printing inks. As more ink is added, less and less light is reflected. Where there is a total
absence of ink the resulting light being reflected (from a white surface) would be perceived as white.

12. HSL and HSB
 Hue Hue is what most people think of when we say "color".
 Saturation Saturation is the "purity" of the color. It refers to the amount of gray paint mixed
with the hue.
 Lightness Value refers to the intensity of light present.

13. HSL and HSB

14. Dithering
 Dithering is often used for displaying monochrome images
 creating the illusion of new colors and shades by varying the pattern of
dots.
 Sometime call halftoning.

15. YCbCr
 YCbCr Color Space is used in MPEG video compression standards
 • Y is luminance
 • Cb is blue chromaticity
 • Cr is red chromaticity
Y = 0.257*R + 0.504*G 0.098*B 16
Cr = 0.439*R 0.368*G 0.071*B 128
Cb = 0.148*R 0.291*G 0.439*B 128
YIQ color space (Matlab conversion function: rgb2ntsc):