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What is Lossless Compression?

Lossless compression reduces data size without discarding information, so decompression can reconstruct the original bytes or pixel values exactly. It usually yields larger files than lossy compression.

How Lossless Compression works

A lossless encoder models redundancy and represents recurring symbols or prediction residuals more compactly while preserving an exact reconstruction target. The target may be a byte stream, decoded pixels, or audio samples, depending on the format’s contract. Entropy and source structure limit the achievable reduction, so already compressed or encrypted inputs may grow after new framing overhead. Media workflows use this mode for masters and intermediate assets when later edits, measurements, or legal preservation require stable source values.

Key facts

  1. “Lossless image” usually guarantees reconstructed sample values, not an identical original file: metadata order, padding, and encoder-specific chunking can change.
  2. Compressing JPEG or other entropy-coded bytes again with a general-purpose lossless codec usually saves little because most easy statistical redundancy is already removed.
  3. Checksums should specify their domain: a file hash verifies container bytes, while a decoded-sample hash can verify media equivalence across different lossless wrappers.

When Lossless Compression matters

Choose lossless coding for source assets, documents, archives, graphics, or data requiring exact round trips. The tradeoff is generally greater storage and bandwidth use than a comparable lossy output.

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