Understanding Image Compression
Image compression is the process of reducing file size by eliminating redundant data while maintaining acceptable visual quality. Understanding how it works helps you make better decisions about quality settings.
Lossy vs. Lossless Compression
- Lossy Compression (JPEG, WebP): Permanently removes some image data to achieve smaller file sizes. The quality slider controls how aggressively data is removed. Higher compression = smaller file = more quality loss.
- Lossless Compression (PNG): Reduces file size without losing any data. File sizes are larger but quality is perfectly preserved. Best for graphics, logos, and images with text.
When to Use Which Format
| Format | Best For | Avoid For |
|---|---|---|
| JPEG | Photographs, complex images with gradients | Text, logos, graphics with sharp edges |
| PNG | Graphics, logos, screenshots, images with text | Large photographs (file size will be huge) |
| WebP | Web images (supports both lossy and transparency) | Print or when older browser support is needed |
Quality Settings Explained
- 90-100%: Minimal compression, nearly indistinguishable from original. Good for archiving.
- 70-89%: Balanced compression, usually no visible quality loss. Ideal for most web use.
- 50-69%: Noticeable compression, minor artifacts may appear. Good for thumbnails or previews.
- Below 50%: Heavy compression, visible artifacts. Only use when file size is critical.
Why Compress Images?
- Faster Websites: Smaller images load quicker, improving user experience and SEO rankings.
- Save Storage: Reduce the space photos take up on your device or cloud storage.
- Email Attachments: Stay under email size limits when sharing photos.
- Social Media: Many platforms compress uploads anyway—pre-compressing gives you more control.
- Mobile Data: Smaller images use less data when browsing or uploading on cellular networks.
Tips for Best Results
- Start High, Go Lower: Begin at 80% quality and decrease until you notice quality degradation, then step back up slightly.
- Check Critical Areas: Pay attention to faces, text, and detailed patterns when evaluating quality.
- Consider the Use Case: Thumbnails can tolerate more compression than hero images.
- Preserve Originals: Always keep an uncompressed backup before compressing important photos.