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ACTIVITY: Image compression

For this activity you will need image editing software, such as Photoshop (for more information, see Image editing programs).
If you are not sure how to download images from the web, go to Downloading images.

  • Download Image 1 to disk. It is currently saved as a high-quality JPEG.

  • Open the image in Photoshop, go to 'File>Save for web' and select JPEG format in the Settings panel at right. Use the tabs at the top to view '4-up' - the original image and three 'optimised' views.

  • Change the 'quality' settings to 20, 40 and 60 in the three optimised views, and see how the image quality and data size changes.

  • Download Image 2 to disk. It is currently saved as a 256 colour GIF.

  • Repeat steps 2-3 above. See how the JPEG format affects the flat colour areas in the graphic.

Image 1 - JPEG

Sample JPEG photo (students)

 

Image 2 - GIF

Sample GIF graphic (temperature chart)