How to compress images without losing quality

KoalaPic offers smart compression that reduces file size while maintaining visual quality.

Using the compressor

1. Go to the Compress page.
2. Upload your image(s).
3. Choose a compression mode:
4. Smart quality — Automatically finds the best quality/size balance using SSIM analysis. Three levels: High (0.98), Medium (0.95), and Low (0.92) similarity thresholds.
5. Target size — Specify an exact target file size (e.g., “under 500 KB”) and KoalaPic will binary-search for the right quality.
6. Manual quality — Set a specific quality percentage (1-100).
7. Click Compress and download.

How smart quality works

Smart quality uses SSIM (Structural Similarity Index) to measure perceptual quality. It performs a binary search across quality levels, comparing each result to the original until it finds the lowest file size that meets your chosen similarity threshold. This means you get the smallest possible file that still looks great.

Tips for smaller files

• WebP and AVIF compress much better than JPG at the same visual quality.
• For photos, JPG or WebP with smart quality is usually the best choice.
• For graphics with flat colors, PNG with quantization gives excellent results.
• Resizing to a smaller dimension before compressing further reduces file size.