Graphical Representation

1
Graphical Representation
Graphics are represented on the computer screen
using pixels. Each pixel may be on or off
depending if the value of that pixel is 1 or 0 in
the computers memory.
2
Screen
Memory
This image is 7 x 7 pixels. The amount of memory
required to store this black and white image is 7
x 7 bits 49 bits.
3
The quality of an image is determined by the
resolution of the graphics available. The smaller
the size of the pixels, the better quality or
higher resolution. Increasing resolution will
increase file size and memory needed to store the
file.

• Graphics can be classified as
• Bitmapped
• Or
• Vector
• Go and look up the difference between vector and
  bit mapped graphics.

4
Bitmap and Vector Images

• Bit map packages paint pictures by changing the
  colour of the pixels which make up the screen
  display.
• Vector packages work by drawing objects on the
  screen.
• Paint - usually bitmapped
• Draw usually vector

5
Main Differences

• When two shapes overlap in a bitmap image, the
  shape on top rubs out whatever is underneath.
• When a vector shape is placed over another shape
  the original shape stays underneath

Vector
Bitmap
Image
6
Differences cont

• When a bitmapped image is saved the whole image
  is saved, whether it contains any of the image.
  This may give large file sizes.
• The objects of a vector drawing are saved as a
  description of their attributes. Eg line
  thickness and coordinates.
• Vector packages are resolution independent
• Resizing of bitmapped images can lead to loss of
  quality and jaggedness
• Resizing of vectors will have little impact on
  file size.

7
Bit Depth

• The number of bits used to represent colours or
  shades of grey in an image is known as bit depth
  or colour depth of an image.

The more bits used for each pixel the larger the
file size.
8
Calculating file sizes

• Storage requirement ( in bits)
• Amount of pixels used in whole image
• number of bits used to represent colours for
• each pixel