How PNG Compression Works
PNG uses lossless compression based on the DEFLATE algorithm (same as ZIP). It applies predictive filtering to pixel rows, then compresses the result. Every pixel is preserved exactly — no quality loss, ever.
PNG optimization works by finding more efficient encoding paths and removing unnecessary metadata. The visual output is byte-for-byte identical to the original pixels.
PNG Compression Results
| Image Type | Original | Optimized | Savings |
|---|---|---|---|
| Screenshot (UI) | 1.8 MB | 720 KB | 60% |
| Diagram/chart | 950 KB | 380 KB | 60% |
| Icon with transparency | 85 KB | 42 KB | 51% |
| Photo saved as PNG | 4.1 MB | 3.2 MB | 22% |
Pro tip: Photos stored as PNG are massively oversized. Convert photos to JPG or WebP first — you'll get 80-90% smaller files. Reserve PNG for graphics, screenshots, and images that need transparency.
When to Use PNG
- Screenshots — sharp text and UI elements stay crisp
- Graphics with text — logos, diagrams, infographics
- Transparency needed — product images on transparent backgrounds
- Pixel art — every pixel matters, no compression artifacts
- Source files — when you'll edit the image later (no generational loss)
When NOT to Use PNG
- Photographs — PNG files for photos are 3-5x larger than JPG. Use JPG or WebP instead.
- Web performance — if file size is critical and minor quality loss is acceptable, WebP offers better compression with transparency support.
- Large images — a 4000×3000 PNG can be 10+ MB. Consider WebP lossless (30% smaller).