9618 · 1.3
Compression — FAQ
Frequently asked questions for 9618 Compression. Direct answers first, then deeper explanation — then practise with marking.
If lossy compression achieves smaller files, why would anyone use lossless?
Because for certain types of data, any loss of information is unacceptable. For example, a compressed text document must be perfectly reconstructable, as changing even one character could alter the meaning. The same applies to software executables, financial data, and scientific measurements where absolute precision is required.
Can you compress a file that has already been compressed?
Yes, but the results vary. Applying lossless compression (like ZIP) to a file that is already losslessly compressed will yield very little or no extra size reduction. Applying further lossy compression to an already lossy file (e.g., re-saving a JPEG) will reduce the file size further but will also cause additional, cumulative quality degradation.
Is there a limit to how much a file can be compressed?
Yes. For lossless compression, the limit is determined by the amount of redundancy in the data. A file with completely random data cannot be compressed losslessly and may even increase in size. For lossy compression, you can theoretically keep compressing until the file is tiny, but it will become completely unusable as all meaningful data is destroyed.
How do I choose which compression to use for my project?
Consider the purpose. Is it for archival? Use lossless (e.g., FLAC for audio, PNG for images). Is it for streaming or sharing online where file size is critical? Use lossy (e.g., MP3/AAC for audio, JPEG/WEBP for images, H.264/H.265 for video). The key is balancing the need for quality against the constraints of storage and bandwidth.