losslessly

Losslessly is an adverb describing methods or processes that preserve all original information, enabling exact reconstruction of the original data from its encoded form. In information theory and data processing, a lossless operation is invertible: applying the operation and then its inverse yields the original input with no information loss. Losslessly encoded data can be decompressed to match the source bit-for-bit.

Lossless compression reduces file size without discarding data, in contrast to lossy compression which permanently removes some information to achieve higher compression ratios. The effectiveness of lossless compression depends on data redundancy and entropy; highly repetitive data compresses well, while highly random data may yield little or no size reduction.

Common lossless formats and techniques include general-purpose compressors such as ZIP, which uses DEFLATE (a combination of LZ77 and Huffman coding), as well as bzip2 and other algorithms. Lossless image and audio formats preserve exact data, notably PNG for images and FLAC or ALAC for audio. Some file types, like TIFF or WAV, can carry lossless options, ensuring faithful reconstruction. Metadata, error detection, and error correction may accompany lossless formats to improve integrity during storage or transmission.

Applications of losslessly compressed or encoded data include software distribution, archival storage, source code preservation, medical imaging, and scientific datasets, where exact replication is required or legally mandated. Limitations include lower compression ratios for data with high entropy and potentially higher CPU usage compared with lossy methods. In practice, losslessly is chosen when fidelity is paramount or when subsequent processing requires exact data recovery.