Image worksheet

Work through these questions before next session

Image editing


Look at the colour panel in Photoshop (Window->Color). Try creating colours by mixing red greem and blue.

Describe the following colours:

  • (100, 0, 0)
  • (100, 100, 240)
  • (100, 100, 100)
  • (100, 100, 30)

What colour values create these colours?


Lossy compression reduces file size but degrades the quality of an image

JPEG is a popular lossy compression format.

Choose an image in Photoshop and save as jpeg. You will get a dialogue box that will allow you to control the quality (there are 3 controls, a number, a slider and words, “high”, “medium” and “low”, they all do the same thing.

Save at a high quality, look at the filesize of the resulting file, and then open it to look at the image. Then save it at really low quality (1) and do the same. The resulting degredations are often called jpeg artefacts


Try the following filters/tools. Do you think they act on single pixels or neighbourhoods?

  • Filter->Blur->Gaussian Blur
  • Image->Adjustments->Threshold
  • Filter->Noise->Add Noise
  • Filter->Pixelate->Facet
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