How Image Compression Works
There are two fundamentally different kinds of compression. Lossless compression (used by PNG) finds more efficient ways to store exactly the same pixels — like zipping a file, nothing is thrown away, but savings are modest. Lossy compression (used by JPG and WebP) discards information your eye is unlikely to notice: fine color variations, high-frequency detail in busy areas, subtle gradients. That's how a 5 MB photo can shrink to 500 KB with no visible difference at normal viewing size.
The quality slider controls how aggressive that discarding is. At 90–95% the output is visually indistinguishable from the original. Around 75–85% you get the sweet spot most websites use — big savings, artifacts only visible if you zoom in. Below 60%, compression artifacts (blocky areas, halos around edges) start appearing at normal size. The right setting depends on the image: photos with lots of texture hide artifacts well; screenshots with sharp text show them quickly.
Why File Size Matters More Than You Think
Images are the heaviest part of almost every web page — typically 40–60% of total page weight. Google's Core Web Vitals measure Largest Contentful Paint (LCP), and on most pages the LCP element is an image. Compressing a hero image from 2 MB to 300 KB routinely cuts load time by more than a second on mobile connections, which measurably improves search ranking, bounce rate, and conversion.
Beyond the web: email providers cap attachments (Gmail at 25 MB), application forms and government portals often enforce limits like "photo under 200 KB", and messaging apps recompress oversized images badly on their own. Compressing yourself, with control over the quality, always beats letting a platform do it for you.
Getting the Best Results
- Resize before you compress. A 4000px-wide photo displayed in an 800px column wastes most of its pixels. Scale it down with the Image Resizer first — resizing usually saves more bytes than compression does.
- Use JPG for photos, PNG for graphics. Photographs compress beautifully as JPG. Screenshots, logos, and anything with sharp edges or text stay crisper as PNG. Our PNG to JPG and JPG to PNG converters handle the switch.
- Compress once, from the original. Re-compressing an already-compressed JPG stacks generations of artifacts. Keep your original and derive each compressed copy from it.
- Check at 100% zoom. Judge quality at the size the image will actually be displayed, not zoomed to 400% — nobody views your website through a magnifier.
Frequently Asked Questions
Will compression make my image blurry?
At sensible settings (75%+), no — the removed detail is below what the eye notices at normal viewing size. Blurriness usually comes from over-aggressive settings or from compressing an image that was already small.
Are my photos uploaded to a server?
No. Compression runs in your browser using the HTML5 canvas API. Your images never leave your device — there's no upload, no queue, and no server-side storage to worry about.
How much smaller will my file get?
Typical photos shrink 60–80% at quality 80. Results vary with content: a detailed landscape compresses less than a portrait with smooth backgrounds, and images that were already optimized may barely change.
Does compressing remove EXIF data?
Yes — re-encoding through the canvas strips metadata such as GPS location, camera model, and timestamps. For photos you're posting publicly, that's usually a privacy win.
What's the difference between compressing and resizing?
Resizing changes the pixel dimensions (4000×3000 → 1200×900); compression keeps the dimensions but stores the pixels more efficiently. For the smallest files, do both — resize to the display size, then compress.