I used to compress at 100% or drag the slider to zero — both wrong
When I first built the Image Compressor, I tested it on a 2.4 MB product photo and got a 180 KB output at 80% quality. I zoomed to 200% looking for artifacts. Could not find any. That is the threshold most people miss: between 75-85% quality, the human visual system genuinely cannot distinguish compressed JPEG/WebP from the original at normal viewing distances.Below ~75%, DCT quantization starts discarding frequency components the eye can detect — hair strands, fabric texture, text on signs. Above 85%, you are spending file size on data the eye cannot resolve anyway.
For PNG, compression is always lossless. The only reduction comes from stripping embedded metadata — EXIF camera data, GPS coordinates, ICC color profiles. A typical camera JPEG can carry 30-120 KB of invisible metadata.
Which format compresses best for your use case
JPEG — Best for photographs, complex scenes with gradients. Lossy. At q=80: 70-85% file size reduction versus uncompressed.WebP — Best for web delivery. Lossy and lossless modes. Typically 25-35% smaller than JPEG at equivalent perceptual quality. Full alpha channel support. To dive deeper, check out my comparison on WebP vs JPEG vs PNG vs AVIF.
PNG — Best for logos, screenshots, anything with sharp edges or transparency. Lossless only. No quality compromise, but limited compression ratio on photographic content.
If you are optimizing for a website: photographs go to WebP, UI screenshots with text go to PNG, product images needing transparency go to WebP.
How to Get the Best Results in Practice
Upload your image to the Image Compressor and start at the default 80% setting. Look at the before/after file size. For most JPEG photos, you will see 60-75% reduction immediately. If the visual looks identical to you at 100% zoom, you are done.For images that will be displayed small (thumbnails, avatars, social media previews), you can often push to 70% without anyone noticing — the image is never viewed at pixel level anyway.
For images containing text or fine line art (screenshots, diagrams, infographics), stay above 85% or switch to PNG. Text edges are exactly the kind of high-frequency detail that lossy compression sacrifices first.
If you are optimizing specifically for web performance, you can read my guide on how to reduce image file size for the web.
Impact on Google Core Web Vitals
Google's Largest Contentful Paint (LCP) metric — one of the three Core Web Vitals that directly affect search rankings — measures how long it takes for the largest image on screen to fully render. If your hero image is 1.8 MB, LCP on a mobile connection will be poor. Compress it to 200 KB and LCP drops proportionally.This is the single highest-impact optimization most small websites can make with zero code changes. Compress the images, re-upload, and the improvement shows up in Google Search Console within days.
What the Tool Does Technically
The compressor uses the browser's native Canvas API: your image is drawn onto an off-screen canvas, then re-exported usingcanvas.toDataURL('image/jpeg', 0.8) or equivalent. The browser's built-in codec handles the actual encoding — the same implementation used by Chrome to display web images. No external library is downloaded, no file leaves your device.