Image compression is one of the highest-impact optimisations you can make, whether you're working on a website, preparing files for email, building a presentation, or submitting documents to an online portal. A 5 MB photo from a modern smartphone camera can become a 300 KB web-ready image with no visible difference on screen. The goal isn't to make images look bad — it's to find the point where smaller file size meets acceptable quality for your specific use case.
Lossy vs Lossless Compression — The Core Concept
Two fundamentally different approaches — and knowing the difference changes which tool you reach for:
- Lossy compression (JPEG, WebP lossy): Permanently removes image data that the human visual system is least likely to notice. Detail in smooth gradients, subtle texture in flat-colour areas, and high-frequency noise are the first to go. At moderate compression (70–85% quality), the loss is imperceptible to the human eye at normal viewing distances. At heavy compression (below 50%), you'll see characteristic 'blocking' artifacts — chunky patterns, especially in areas of flat colour and around sharp edges.
- Lossless compression (PNG, WebP lossless, GIF): Rearranges the data more efficiently without discarding any information. Every pixel in the decompressed image is identical to the original. File size reduction is smaller than lossy — typically 10–30% for photos, sometimes 50–60% for graphics and screenshots with large flat-colour areas.
- Knowing which type you need: photos almost always benefit from lossy compression. Screenshots, logos, diagrams, and graphics with text are better served by lossless — lossy compression makes text look blurry and creates artifacts on hard edges.
How to Compress Images Free with Convifi
Your photos stay on your device — Convifi compresses them locally in the browser.
- Go to convifi.com/compress-images
- Drop your image onto the page (JPEG, PNG, WebP supported)
- Adjust the quality slider — start at 80% and preview the result
- Adjust the max dimension if you want to resize as well as compress
- Download the compressed image
What Quality Setting Should You Use?
No single number is right for everything. A reasonable starting point by situation:
- Website hero images and banners: 75–82% quality. These are viewed full-screen but only need to look good on a monitor, not printed.
- Product photos for e-commerce: 82–88% quality. Customers zoom in on product images, so detail matters.
- Blog post inline images: 70–78% quality. Rarely examined closely, heavily trafficked pages benefit from small files.
- Email attachments (photos to family/friends): 65–75%. Email bandwidth matters; recipients view on screens.
- Printing: 90–95% quality or lossless. Print exposes compression artifacts that screens hide.
- Passport/ID photos for portals: 85% quality, resize to the required dimensions first.
PNG Screenshots and Diagrams
PNG files containing screenshots, UI mockups, or diagrams with text should be compressed losslessly rather than with lossy JPEG compression. JPEG compression makes text and sharp lines look fuzzy — it's the wrong tool for this content type. Convifi's PNG compressor uses lossless algorithms to reduce PNG file sizes by 10–40% with zero visible change.
WebP: The Upgrade Worth Making
If you're compressing images for a website, consider converting to WebP instead of JPEG. WebP delivers the same visual quality at 25–35% smaller file sizes. A 200 KB JPEG hero image becomes a 130 KB WebP with identical visual quality. Chrome, Firefox, Safari (since 2020), and Edge all support WebP natively — browser support is now above 97% globally. Use the PNG to WebP converter on Convifi before compressing.
Real-World Size Examples
Some real numbers:
- A 5 MB camera JPEG → 450 KB at 80% quality. 89% smaller. Indistinguishable on screen.
- A 1.2 MB PNG screenshot → 400–600 KB lossless. 50% smaller. Pixel-identical.
- A 3 MB product photo → 280 KB at 82% WebP. 91% smaller. Looks identical on most monitors.
- A 800 KB profile photo → 60–80 KB at 75%. Appropriate for any social media or website profile.
Resizing vs Compressing
Image compression and image resizing work together. If your image is 4000×3000px but will only ever be displayed at 1200×900px, resizing it to 1200×900px before compressing dramatically reduces the file size — because there are fewer pixels to store. Convifi's Max Dimension slider lets you set the longest side of the output, capping resolution while preserving aspect ratio. For web images, 1920px width is the maximum you'll ever need. For thumbnails and previews, 800px or even 400px is sufficient.