Lossless vs Lossy Image Compression: What Is the Difference?
A clear explanation of lossless and lossy compression — when to use each, which formats use which, and how to choose for your use case.
Every time you compress an image, you are using either lossless or lossy compression — two fundamentally different approaches with very different tradeoffs. Understanding the difference helps you choose the right format and the right tool every time.
Lossy Compression: Smaller Files, Some Data Discarded
- Lossy compression permanently removes image data that the compression algorithm considers least important. The removed data cannot be recovered. The result is a smaller file — but each time you re-compress a lossy file, it loses more data.
- Formats that use lossy compression:
- JPG / JPEG
- WebP (lossy mode)
- AVIF (lossy mode)
- HEIC (lossy mode)
- Best for: Photographs, social media images, web content — anywhere that small file size matters more than pixel-perfect preservation.
Lossless Compression: Same Quality, Just Organised Better
- Lossless compression reorganises image data more efficiently without discarding anything. The decompressed file is bit-for-bit identical to the original. Files are larger than lossy, but quality is perfectly preserved.
- Formats that use lossless compression:
- PNG
- WebP (lossless mode)
- TIFF (with LZW compression)
- GIF (limited to 256 colours)
- BMP (uncompressed, technically lossless)
- Best for: Logos, screenshots, medical images, archival photos — anywhere pixel accuracy is critical.
The Practical Difference in File Size
| Image Type | JPG (lossy) | PNG (lossless) | WebP (lossy) |
|---|---|---|---|
| Photograph (1200×800) | ~120KB | ~800KB | ~90KB |
| Screenshot (1920×1080) | ~200KB | ~150KB | ~100KB |
| Logo (500×200) | ~30KB | ~15KB | ~10KB |
Generation Loss: The Key Risk with Lossy Compression
Every time you open a lossy file and re-save it, it loses more data. Save a JPG 10 times and you can see visible artefacts. This is called generation loss. The solution: always keep your original in a lossless format (PNG or TIFF) and export a new lossy copy for distribution each time. Never re-save a JPG repeatedly.
Which Should You Use?
- Photos for the web: Lossy JPG or WebP — Compress images here
- Logo or icon: Lossless PNG — Convert to PNG
- Photo archive / master file: Lossless TIFF or PNG
- Best of both worlds for the web: WebP supports both — Convert to WebP
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