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Basic Computer Graphics I

What Makes An Image Digital?

  • Ones & Zeros
    It's not:
  • Film
  • Print
  • Paint on Canvas, Pencil on Paper...
  • It's Not Real
  • So what is it anyway?

Pixels

The smallest unit of display information on the screen

  • Described in three dimensions:
    • (X) Horizontal location from the left side of the screen
    • (Y) Vertical location from the top of the screen
    • (Z) Color of pixel at the location
 

Colors

Color of pixel at the location is one of a set of colors determined by the Bit Depth of the image

Bit Depth

  • What is Depth?
    • If an image is X pixels wide and Y pixels high, then it can be said to have a depth of Z
  • What is a Bit?
    • 1 or 0
    • Bits can be used for binary arithmetic

Binary

Power of 2

Decimal

Hexadecimal

1
10
100
1000
10000
100000
1000000
10000000
100000000

2 to the power of 0
2 to the power of 1
2 to the power of 2
2 to the power of 3
2 to the power of 4
2 to the power of 5
2 to the power of 6
2 to the power of 7
2 to the power of 8

1
2
4
8
16
32
64
128
256

1
2
4
8
10
20
40
80
100

Decimal

 0000000100020003000400050006000700080009 001000110012001300140015

Hexadecimal

 0000000100020003000400050006000700080009 000A000B000C000D000E000F

Binary

 0000000100100011010001010110011110001001 101010111100110111101111
  • Color Depth is measured in bits
    • 8 bits: 10010100: 256 possible combinations
      (2 to the 8th power or 2x2x2x2x2x2x2x2)
    • 24 bits: 101010011010100101011001: 2 to the power of 24
      • 3 sets of 8 bits for Red, Green and Blue (RGB)
        • Demo Photoshop's Color Palette
    • 32 Bit
      • 3 sets of 8 bits for RGB, one set for transparency
  • Beyond 32 bits…

Bitmaps Vs. Vectors

  • Bitmaps are bound to the individual pixels that describe them
    • Changing size means loosing information
    • They tend to fall apart when you make them bigger
  • Vectors are bound to mathematical formulas that describe them
    • Changing size does not really affect them
    • They tend to be smaller in file size
    • They tend not to be as detailed as bitmaps
  • Let's Compare
  • Illustrator & work in both, but…
    • Illustrator is optimized for vectors
    • Photoshop is optimized for bitmaps

Anti-Aliasing

  • Aliasing is what happens when solid colors don't conform to vertical and horizontal edges
  • Anti-aliasing is the process which softens the "stair steps" of aliasing through color interpolation

Break

Assignment 1

Pixel Poking

Here's pixelpoker

  • Mac OS X has a built in screen capture utility
    • Shift-Command 3 for the entire screen
    • Shift-Command 4 for a selection
    • The captured image is saved as a file to the desktop called "picture 1.png"
    • You will need this to complete your assignment
      1. Edit the pixelpokers 4 samples
      2. Screen-capture each one
      3. Bring the capture into Photoshop and crop it to just the pixel grid