Glossary A–ZLetter C
Compression
Compression reduces the size of files by storing data more efficiently.
A distinction is made between lossless compression, which restores the original completely, and lossy compression, which leaves out details that are barely visible to the eye.
For images, JPEG is an example of lossy and PNG of lossless compression. Videos are almost always compressed lossily; the video codec determines the method, and the bit rate determines its strength. For screen networks, compression is what makes it possible to transfer and store videos at all, because uncompressed they would be many times larger.
Too much compression shows up as blocky artefacts, smeared areas and banding in gradients, which are particularly noticeable on large screens viewed from close up. Fine type and sharp edges suffer more in videos than photos do. Operators should therefore compress content only once from the original file; repeated recompression degrades the picture with every pass. Text and logos often look better as a separate layer than burnt into the video.