Digital image : a matrix of pixels.

Pixel: picture element, unit for screen and digital images.

Resolution: pixel density.

Screen: 1024x768
Printer 300 dpi (dots per inch)
Picture: 76 dpi

B/W: 1 bit/pixel
16 colors: 4 bits/pixel
256 colors or grays : 8 bits/pixel
True color : 32 bits/pixel

Electromagnetic spectrum: radio, TV, phones, radar, microwave, infrared (heat), visible light, ultraviolet, X-rays, Gamma-rays.

Light properties:

electromagnetic wave
frequency (f) and wavelength (l) : c=fl
white light: contains all visible frequencies
red frequency < violet frequency
energy : white energy Ew and dominant energy Ed

Color composition

• Mixing (subtracting): blue + yellow = green, green + red = black
• Composing (adding): blue + yellow = white, green + red = yellow

Primary colors: can produce the others from them

mixing : red, yellow, blue (painting)
composing : red, green, blue (vision, computer screen)

mixing : red - green, blue - orange, yellow - violet
composing : red - cyan, green - magenta, blue - yellow

TV / screen: matrix of RGB dots.

Printer : matrix of CMY + Black dots.
RGB: red, green, blue
[0, 1] [0, 1] [0, 1] or [0, 255] [0, 255] [0, 255]
CMY: cyan, magenta, yellow – printing
[0, 1] [0, 1] [0, 1]
HSV: hue, saturation, value – painting programs
[0, 359] [0, 1] [0, 1]
 
 
 

RGB	CMY
See Fig. 2-1 from the textbook	See Fig. 2-2 from the textbook.

(C, M, Y) = (1, 1, 1) - (R, G, B)

• System colors (Unix-Linux), HTML, some libraries.
• 256 named colors: red, tan, navy, salmon, orange, etc.
• List of the system colors: emacs – Edit – Text Properties – Display Colors
• xterm –bg chocolate4 –fg wheat

set of primitives like lines, rectangles, spheres, etc., given by coordinates
xfig, ClarisDraw, etc.
high level of compression, easy editing
shape restrictions

set of individual pixels
direct RGB / lookup table  or color map
true color   /  256 colors or grayscale

GIF (Graphics Interchange Format) 256
JPEG (Joint Photographic Experts Group) true
BMP (Windows bitmap) 2-true
TIFF (Tagged Image File Format) true
TGA (Targa File, SUN) true
PNG (Portable Network Graphics) 256
EPS (Encapsulated PostScript) true

format identification
image size
image type
image data format
compression type

color map
pixel data (raster)

Graphic Scene and Components

• The elements composing an image are usually called a "scene".
• What makes the image:
  • viewer or camera, position, orientation, angle, type of projection, clipping window
  • objects: geometry, spatial relationship, colors, material properties
  • light sources: position, type, intensity, color
  • how they are all connected