Compression

• Maximizes the amount you can store on a device
• Compression reduces the size of a file so it takes up less space
• Smaller files are quicker when transferred (streamed) over the Internet
• With an image, the number of colours increases the file size because more bits per pixel are needed to store a greater range of possible colours
• One way to make the file size smaller is to store a lower number of colours or to store bigger areas of pixels as one colour
• Both of these techniques will reduce the quality of the image and are known as lossy compression
• Lossless compression does not lose any data at all during compression
• In images with large areas of repeating colour, instead of storing every pixel, we can store the binary for the colour followed by the number of pixels in a row
• Works well with images that have lots of repeating colour, but does not work well with full colour photographs
• Some types of files like text documents and executable code must be compressed without any loss of data, so we use lossless compression for these files
• Reducing the number of bits in a file makes the storage capacity lower and data transfer quicker
• Lossy compression: Some data is lost and cannot be recovered, greatly reducing the file size and reducing the quality of the image/sound. Suitable for images, sound, and video, but not for text and executable files
• Lossless compression: None of the data is lost, it is encoded differently and can be turned back into the original format. Can be used on all types of data, but is usually less effective than lossy compression at reducing file size. Most suitable for documents and executable files