File Compression
What is File Compression?
Every digital media file — whether an image, an audio track, or a video — takes up storage space. Uncompressed files store all of their data in full, which means high quality but large file sizes. Large files are slow to upload, slow to stream, and costly to store, especially at scale.
File compression is the process of reducing a file's size by encoding its data more efficiently or by removing some of it altogether. The aim is to make files easier to store, transfer, and distribute — without making the quality unacceptably poor for the intended use.
There are two fundamentally different approaches: lossy compression and lossless compression. Understanding both — and knowing when to use each — is essential for the exam.
Lossy Compression
Lossy compression permanently removes data from a file in order to reduce its size. The data that is discarded is chosen carefully — it tends to be information that human senses are least likely to detect. In an image, this might be subtle colour differences between neighbouring pixels. In audio, it might be quiet sounds drowned out by louder ones playing at the same time.
Because the removed data is gone permanently, a lossy file cannot be restored to its original quality. Each time a lossy file is edited and re-saved, another round of compression discards more data, causing quality to degrade further. This process is sometimes called generation loss.
The key advantage is the dramatic reduction in file size that lossy compression achieves. An MP3 audio file might be a tenth of the size of the equivalent WAV file; a JPEG image might be a fraction of the size of a TIFF. This makes lossy formats ideal wherever smaller file sizes matter more than perfect quality — streaming music, social media images, and online video are all contexts where lossy compression is the standard.
Examples of lossy formats across media types: JPEG (image), MP3 and AAC (audio), MP4 and WMV (video).
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