Computer Studies
 Knot Making

Graphics compression

  • There are mainly three types of graphic formats:
    • Bitmap
      • .bmp filenames
      • for each pixel, the bitmap format records information
      • it takes a large amount of Hard Disk space.
    • Graphics Interchange Format
      • .gif filenames
      • used for pictures with large areas of same colour
      • groups areas of same colour together
    • Mpeg
      • .jpg filenames
      • use a high compression algorithim
      • called jpeg
      • used for photos because these have no groups of pixels next to each other which are the same.


  • Enter the paint program and save a blank picture in the document
  • Note that the file size should be very small as the picture is blank. But, it is large.
  • Draw in the picture and save it again, now check with the supposition that it should be a larger filename. But, it is still the same size.
  • Now save the same picture as GIF and note the slight change of colour tones. Now see the file size and it should be relatively minute.
  • Now save the picture as a JPG and this time note the large difference in colour tones and definition. Check the filesize.
  • Open a photo quality bitmap and note that no pixel is the same as its adjacent.
  • Save as GIF and note the poor quality it becomes, and small size on disk.
  • Lastly, save it as a JPG and note the negligible difference it makes, note itís smaller size on disk.

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