Lossy vs. lossless: what you lose when you compress
Image compression comes in two flavors. Lossless compression squeezes a PNG without throwing away any pixels—you get the exact same image back, just in a smaller file. Lossy compression, used by JPEG, throws away some data to achieve bigger file size reductions. JPEG discards high-frequency color information your eye barely notices, but each time you re-save a JPEG, you lose more detail. Save a JPEG 10 times and it gets visibly blotchy (called generation loss). PNG doesn't suffer this—you can re-save it forever and never degrade.
For photos, lossy JPEG is almost always the right choice. A JPEG at quality 80–85 looks excellent and compresses 10× smaller than the original. For screenshots, diagrams, or images with text, PNG is better—it preserves sharp edges. WebP and AVIF are modern alternatives that beat JPEG at compression (30% smaller at the same quality), but older browsers don't support them.
Understanding JPEG quality
- Quality 50–65: Visible artifacts, noticeable color banding. Only useful if file size is the absolute priority and visual quality doesn't matter.
- Quality 75–85: Sweet spot. Compression is excellent, and artifacts are invisible at normal viewing distance. This is what most web images should target.
- Quality 90–95: High quality, but file sizes are larger. Only needed for archival, professional photos, or print. Most viewers won't see the difference from quality 85.
- Quality 100: Still lossy—the JPEG algorithm is being used, just with minimal compression. File sizes are huge. Use lossless PNG if you want true quality 100.
Real-world compression wins
A 5 MB iPhone photo compressed to JPEG quality 82 drops to 400 KB. That's a 92% reduction—perfect for uploading to Gmail (which has 25 MB per email) or sending over mobile data. Resizing the photo to 1920px wide (from original 3000px) before compressing saves even more—you're not uploading pixels you don't need.
Website performance improves dramatically when images are compressed. A hero image at 800 KB slows page load; at 120 KB (same dimensions, quality 80), it loads instantly. Social media platforms (Instagram, Twitter, Facebook) recompress your uploads anyway, so over-optimizing is pointless, but basic compression is essential.
Never recompress a JPEG. Download the original, re-save at quality 80, and you're fine. Re-compress a JPEG that's already been compressed, and you get generation loss that stacks. Always keep your source images, and derive web versions from the originals.
Frequently asked questions
Why does my PNG look the same size after compression?
PNG uses lossless compression. If it's a photo with millions of colors, there's not much redundancy to squeeze. You get maybe 10–20% smaller. If you need aggressive compression, convert to JPEG (sacrificing lossless-ness) or use WebP/AVIF.
What's WebP and why don't I see it everywhere?
WebP is Google's format—it's 25–35% smaller than JPEG at the same quality. Internet Explorer and older versions of Safari don't support it, so adoption is slow. For web use, it's the future, but JPEG is still the universal fallback.
Can I crop and compress in the same step?
Not with this tool—it compresses without resizing. But cropping before compression is always smarter: fewer pixels means smaller file. If you want to crop first, use the Image Cropper, then compress the result.
Is there a "good enough" compression setting for all images?
Quality 80 for JPEG works for 90% of photos and web use. For print or archival, go 90+. For email or mobile, 75 is fine. Experiment with a test image and adjust by eye—the quality slider shows you the impact in real-time.