Topic 16-Digital Imaging

Topic 16- Digital Imaging

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Topic 16-Digital Imaging

Two types of graphic:

  • Bitmap
  • Vector

Bitmap: photograph

  • Image itself is stored as a map showing the position of each pixel
  • Details of the colour of each pixel are stored
  • This is a huge amount of data

In general:

  • Bitmap are big files so they take lots of space on a disk. They also take a long time to upload (i.e.put onto a website) or download (i.e. to appear on a user's screen)
  • They can lose their sharpness when they are enlarges or reduced in size

Vector: drawing

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Topic 16-Digital Imaging

  • Information about how to draw the image is stored rather than the image itself
  • Stored as a series of wquations
  • The equations tell the computer how to draw the parts of the image
  • Only instruction/equations are stores, so file size is small

In general:

  • Are used for more precise images such as: maps, technical, drawing/plans or images that contain a limited number of colours
  • Are not good for re-creating photgraphic type artwork
  • Are uploaded and downloaded faster owing to their smaller file size
  • Can be enlarged or reduced, keeping their sharpness
  • Do not take up much space when stored compares to bitmap images 
  • Are made up of objects that can be edited and filled with colour

Impact of large file size for bitmap:

  • Large file size means large upload time (i.e. time to transfer file to a website is large)
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Topic 16-Digital Imaging

  • Large file size means download time is large (i.e. the time taken for a user to view the image on a website)
  • Files are compressed to reduce file size

Impact of small file size for vector graphics:

  • Quick upload time
  • Quick download time
  • Can store lots more images in the same storage space compared to bitmap

Advantages of vecotr graphics compared to bitmap graphics:

  • Vector graphics have very small sizes. Small file size means that a viewr or the graphics does not wait long to see it appear on the screen
  • They have a low upload and download time and so are ideal for the Web 
  • They are much easier to edit and can be resized without any loss in quality
  • By using software it is easy to zoom in and out a vector image

Disadvantages of vector graphics:

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Topic 16-Digital Imaging

  • Only suitable for images with a limited number of colours
  • No good for images with continuous colours like a photograph

Tootls and techniques used for manipulating still images:

  • Graphics can be manipulated in a number of ways including:
  • Zoom: allows a user to magnify or reduce the size of an image on a screen
  • Selections: allows the whole or part of an image to be selected for editing
  • Transformationing: using rotation or reflection
  • Sizing: the graphic is pre stored at a certain size but can have its size altered
  • Scaling: is sizeing to a pre determied size often expresseed as a percentage
  • Copying: a single image can be copied many times
  • Moving: an image can be moved to any place where it is suitable
  • Layering: add elements to an image that exists serparately

Colour effects:

  • There are many imaging effects that can be used on a pictiure:
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Topic 16-Digital Imaging

  • Colour palette
  • Gradient tool

Image effect:

  • There are many imaging effects that can used on a picture
  • Touch up
  • Red eye reduction 
  • Smoothing

Common File Formats:

  • GIF file- graphical interchange format. Original image is compressed. They have the advantages that they are small in file size. A max of 256 colours can be used, this means don't quite look like the original image. They are good for images and photographs on the web
  • JPEG- Joint Photographic Expert Group. Ideal for photos. Original image is compressed. Uses 16 million colours
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Topic 16-Digital Imaging

GIF file format:

  • Uses 8 bits for colours
  • Maximum of 256 colours 
  • Transparency
  • Uses compression 
  • Used for simple graphics

JPEG files format:

  • Uses 24 bits for colour
  • Maximum of 16.7 million colours
  • Uses compression
  • Used images with continuous colour (e.g. photos)
  • Transparency 

Other common file formats:

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Topic 16-Digital Imaging

  • PNG- Portable network Graphics
  • TIFF- Tagged Image File Format
  • PSD- PhotoShop Document
  • BMP-BitMaP
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