File Size Reduction (Cambridge International IGCSE ICT)

File Compression

Spec point — 11.2.2

What is file compression?

• File compression is reducing the size of a file in order to take up less storage space and make file transmission faster

• Images are often the largest element of a file and can be resized/resampled by:

  • Reducing the resolution
  • Reducing the colour depth

Resolution

• Resolution is the total amount of pixels that make up an image
• The resolution is calculated by multiplying the height and width of the image (in pixels)
• In general, the higher the resolution the more detail in the image (higher quality)
• Reducing resolution decreases the number of pixels and therefore reduces file size
• Be aware that reducing resolution can cause a loss of image quality, especially when viewed at larger sizes

Colour depth

• Colour depth is the number of bits stored per pixel in an image
• The colour depth is dependent on the number of colours needed in the image
• In general, the higher the colour depth the more detail in the image (higher quality)
• Reducing colour depth means using fewer bits and therefore fewer colours, which can reduce the file size
• Like with resolution, reducing colour depth can lead to a loss of image quality