Definition: lossy compression

A compression technique that does not decompress digital data back to 100% of the original. Lossy methods can provide high degrees of compression and result in smaller compressed files, but some number of the original pixels, sound waves or video frames are removed forever. Examples are the widely used JPEG image, MPEG video and MP3 audio formats.

The greater the compression, the smaller the file. However, a high image compression loss can be observed in photos printed very large, and people with excellent hearing can notice a huge difference between MP3 music and high-resolution audio files (see audiophile). Typically, the moving frames of video can tolerate a greater loss of pixels than still images.

Lossy compression is never used for business data and text, which demand a perfect restoration (see lossless compression). See data compression, codec examples, JPEG, MPEG and MP3.

Lossless vs. Lossy Compression

Business data requires lossless compression, while audio and video applications can tolerate some loss, which may not be very noticeable.

Sometimes Hard to Tell

The top JPEG image is one fifth the file size of the bottom image, which was compressed the least. Look carefully at the orange section on the top of this cake.

Easier to See With Text

The top JPEG image was compressed the most, and the text is not as sharp as the least compressed. The bottom blow-up shows the distortion clearly.

Lossless GIFs Are Better for Text

The same text is saved in the lossless GIF format. Not only is it as sharp as the least-compressed JPEG, the GIF file is almost 1/10th the size.