How to Compress an Image Without Losing Quality
"Without losing quality" is a spectrum, not an absolute. Here is how to find the sweet spot - a file that is 60-80% smaller with no visible difference.
By imgresizer.org · Feb 20, 2026 · 5 min read
Lossy vs lossless compression
There are two fundamentally different approaches to image compression:
Lossless
Every pixel is preserved exactly. The file is smaller because redundant data is encoded more efficiently - but there is a ceiling on how small it can get. Used by PNG, lossless WebP, and lossless GIF.
Lossy
Some information is permanently discarded. The algorithm identifies what human vision is least sensitive to and removes it. Used by JPG, WebP (lossy mode), and HEIC. Can achieve 80-90% size reductions.
The quality setting explained
For JPEG and WebP, a "quality" slider controls how aggressively the algorithm discards data. The relationship between quality number and file size is not linear:
Quality 90-100%Barely distinguishable from the original. File is still large - often only 10-20% smaller than uncompressed.Quality 80-90%The sweet spot for most photographs. Invisible compression artifacts in almost all real-world images. Files are 40-70% smaller than quality 100.Quality 70-80%Slight artifacts visible in flat-colour areas and around high-contrast edges. Acceptable for thumbnails and social media.Quality 50-70%Visible blocking and smearing. Only appropriate for placeholder images or tiny thumbnails.Quality < 50%Significant degradation. Not recommended except for heavily downscaled images.
Recommendation: start at 82% and go lower only if you need a smaller file and the image still looks acceptable at 100% zoom.
Resize first, then compress
The biggest contributor to file size is often the number of pixels - not the quality setting. A 4000 × 3000 px photo that will only be displayed at 800 × 600 px on screen does not benefit from its extra resolution.
A practical workflow:
- Use the Resize Image tool to set the maximum dimension to your actual display size (e.g. 1200 px wide for a blog post).
- Then use the Compress Image tool at quality 82% to reduce the file size further.
This two-step approach routinely reduces file size by 85-95% compared to the original camera file.
Format matters more than quality settings
Choosing the right format can cut file size more than any quality setting:
- Photo on a website:Convert to WebP. Same visual quality as JPG at 25-34% smaller file size.
- Photo in an email:JPG at quality 80-85%. WebP has poor email client support.
- Logo or icon:PNG for lossless, or WebP (lossless) for smaller. Never JPG - it creates artifacts on sharp edges.
- Screenshot with text:PNG or lossless WebP. JPG creates visible blur around text.
The encoder matters
Not all image tools produce the same output quality. A tool that looks identical on the surface can produce files that are 10-20% larger than necessary because of how it encodes the output.
imgresizer.org uses production-grade WASM encoders (mozjpeg for JPEG, libwebp for WebP, oxipng for PNG) that consistently produce smaller files at the same visual quality compared to standard browser-based tools - without any extra steps on your end.
Compress your images