In this chapter, you will learn

1
In this chapter, you will learn

• How computer handles graphic objects
• The differences between a bitmap file and a
  vector file
• The differences among different common graphic
  file formats

2
Handling Computer Graphics

• Computer Handles data in binary format 0 or 1
  (bit)

28 256
216 65,535
224 16,777,216
232 4,294,967,296
3
Bitmap Graphics

• A bitmap graphic is represented by a dot pattern
• Each dot is called a Pixel (picture element)
• A pixel has a single color only

4
To have a better understanding of bitmap
graphics, lets start with the simplest type of
bitmap picture - Monochrome (i.e. BW) Bitmap
5
BW Bitmap Graphics

• A pixel can be Black or white (2 states)
• So, 1 bit can be used to code the color

1111111111111 1111111111111 0001111111111 10111111
11111 1100011111111 1111000111111 1111110111111 11
11111000011 1111111111001 1111111111110 1111111111
110 1111111111111
1 - White 0 - Black
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BW Bitmap Graphics

• Therefore, a full screen (800 x 600) monochrome
  bitmap picture requires storage of
• (800 x 600 x 1) bits
• 480000 bits
• 60000 bytes
• 58.59 kB

7
Grayscale Bitmap Graphics

• Grayscale graphics are created by using shades of
  gray
• 8 levels of grayscale

How many bits should be used to represent the
gray colors of each pixel?
3 bits
8
256 colors Bitmap Graphics

• How many bits are necessary to represent 256
  colors in each pixel?

8 bits
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Question

• How many bits are necessary to represent a 800 x
  600 graphic of 256 colors?

Number of bits used 800 x 600 x 8 bits
3,840,000 bits
(Storage required 468.75 kB)
The larger the resolution and the no. of colors,
the more storage spaces are required to hold the
graphic
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Vector Graphics

• A vector graphic is divided into objects
• Each object is defined by the method of drawing
  it

This picture contains 3 objectsa line, a circle
and a rectangle
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How to draw the circle?

• The circle is represented by a mathematical
  formula

Circle(50,100,150,black,1,green)
A few bits is enough to save the properties of
this circle!
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Advantages of using Vector Graphics

• It requires less storage space
• When a vector graphic is enlarged, it remains
  intact (no distortion)

Enlarging a Vector Graphic
The line is as smooth as before
Enlarging a Bitmap Graphic
The line thickened saw-tooth resulted
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Common Graphic File Format

• Bitmap (.bmp) - a common graphic file
  formatcan be read by almost all programs
• Gif (.gif) - a compressed bitmap file format. It
  can support up to 256 colors
• Jpeg (.jpg) - a lossy compressed bitmap file
  format. But it can support up to 16.7 million
  colors
• (because it applies lossy compression, some of
  the details is lost!)

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Jpeg Format (5kB)
Gif Format (26kB)
15
Comparison Table
16
How colors are represented?

• 8-bit color means 28 256 different colors
• 16-bit (High) color means 216 65535 different
  colors
• 24-bit (True) color means 224 16777216
  different colors

The number of bits used to represent colors is
called color depth.
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RGB Color Scheme

• All colors are made up of 3 primary colors of
  light Red (R), Green (G) and Blue (B)
• Different intensities of red, green and blue can
  mix up different colors
• In computer, 8 bits are used to represent 256
  levels of each of these primary colors

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Example
Http//www.phy.ntnu.edu.tw/hwang/image/rgbColor.h
tml

• RGB(255,0,0) Red
• RGB(0,255,0) Green
• RGB(0,0,255)
• RGB(0,0,0)
• RGB(255,255,255)
• RGB(255,0,255)

Blue
Black
White
Magenta
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CMYK Color Scheme

• For printing, publisher will find CMYK scheme
  more suitable for ink used.
• CMYK represents 4 colors Cyan, Magenta, Yellow
  and blacK.