IGCSEComputer ScienceCIERevision Notes1. Data Representation1.2 Text, Sound and ImagesRepresenting Images

Representing Images (CIE IGCSE Computer Science)

Revision Note

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Becci Peters

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Computer Science

Representing Images

  • A bitmap image is made up of a series of pixels, which are small dots of colour that are arranged in a grid. Each pixel can be represented by a binary code, which is processed by a computer
  • The resolution of an image refers to the number of pixels in the image. A higher resolution image has more pixels and is, therefore, sharper and more detailed but also requires more storage space
  • The colour depth of an image refers to the number of bits used to represent each colour. A higher colour depth means that more colours can be represented, resulting in a more realistic image but also requires more storage space
  • E.g. an 8-bit colour depth allows for 256 different colours to be represented (28=256), while a 24-bit colour depth allows for over 16 million different colours to be represented (224=16,777,216)
  • The file size of an image increases as the resolution and colour depth increase. This is because more pixels and colours require more binary data to represent them
  • The quality of an image also increases as the resolution and colour depth increase. However, it's important to balance the desired quality with the practical limitations of storage space

Worked example

An image has a resolution of 600 x 400 and a colour depth of 1 byte. Calculate the file size of the image giving your answer in bytes. Show your working

[2]

  • 600 space cross times space 400 space equals space 240000 [2]
  • 1 mark for the working and 1 mark for the answer

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    Becci Peters

    Author: Becci Peters

    Becci has been a passionate Computing teacher for over 9 years, teaching Computing across the UK helping to engage, interest and develop confidence in the subject at all levels. Working as a Head of Department and then as an educational consultant, Becci has advised schools in England, where her role was to support and coach teachers to improve Computing teaching for all. Becci is also a senior examiner for multiple exam boards covering GCSE & A-level. She has worked as a lecturer at a university, lecturing trainee teachers for Computing.