DEFLATE

DEFLATE is a lossless data compression algorithm specified in RFC 1951. It combines two techniques: LZ77 (finding repeated substrings and replacing them with back-references) and Huffman coding (assigning shorter binary codes to more common symbols).

DEFLATE is the compression algorithm behind PNG image files, ZIP archives, gzip-compressed files (including HTTP Content-Encoding: gzip), zlib library data streams, and Git’s pack files. It’s arguably the most-deployed compression algorithm in computing history.

Characteristics:

• Lossless — original bytes recoverable exactly.
• Fast to decompress, moderately fast to compress.
• No external dictionary, so any DEFLATE stream is self-contained.
• Good for text and structured data; mediocre for already-compressed media.

Newer algorithms (Brotli, Zstandard) compress better and are increasingly common on the web, but DEFLATE remains the universal fallback because every browser, OS, and tool supports it.