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.

Practice:

• 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 it’s smaller size on disk.