How Computers Represent Graphics

How computers representHow computers representgraphicsgraphics

GraphicsAn image is made up of tiny dots called pixels.

The resolution determines the quality of the picture. The smaller the pixels the finer the detail that can be displayed on the screen.

High Resolution Image Low Resolution Image

Graphics PackagesGraphics packages can be classed as either:

Bitmapped graphics (painting) Vector graphics (drawing)

Bitmapped GraphicsThe image is saved in a two dimensional array using binary numbers to represent the colours in the pixels. Each pixel is represented by the same number of bits.

In this example, two colours have been used (black/white) and so each pixel is represented by one bit.

0 = white, 1 = black

Bitmapped GraphicsIn this example, four colours are used in the graphic and so each pixel is represented using two bits.

00 = white, 01 = blue, 10 = red, 11 = black

Bitmapped GraphicsHow many colours could be represented using 3 bits?

Bitmapped GraphicsHow many colours could be represented using 3 bits?

000

001

010

011

100

101

110

111

8 colours (23) could be represented using 3 bits

Bit DepthThe number of bits used to represent the colour of the pixels is called the bit depth.

Colours Bits

2 1

4 2

8 3

16 4

32 5

64 6

128 7

256 8

65536 16

16777216 24 (True Colour)

CreditsCfE Computing – How computers represent graphics

Produced by P. Greene and adapted by R. G. Simpson for the City of Edinburgh Council 2004

Adapted by M. Cunningham 2011

All images licenced under Creative Commons 3.0• Sets of blue waves and surfing boards by Horia Varlan (Flickr)• Black & White Atlanta skyline by Glen Edelson (Flickr)• A Cactus Flower for Capt. Suresh by Koshy Koshy (Flickr)• Sunset over the Danube - Budapest by joiseyshowaa (Flickr)• Edinburgh skyline by rovingI (Flickr)