JPEG is still the most widely used photo format, and many JPEGs straight from cameras or design tools are 2–5× larger than they need to be. The good news: with MozJPEG and the right quality, you can cut 50–70% of the bytes with no visible quality loss. Here's how.
Why MozJPEG beats standard JPEG
Standard JPEG encoders (libjpeg) are decades old. MozJPEG is a modernized encoder that produces smaller, better-looking files at the same quality setting by using optimized quantization tables and progressive scanning. Kix Image Tools uses MozJPEG, so you get the better encoder by default.
The quality sweet spot
JPEG quality is 1–100, but the scale isn't linear — there's a cliff:
- 90–100: almost no perceptible difference vs source, but files stay large. Usually wasteful.
- 75–85: visually clean for almost all photos. The best balance.
- 60–70: minor artifacts on close inspection, fine for thumbnails.
- Below 50: blocking and banding become obvious.
For most photos, quality 75 is the sweet spot — and it's Kix Image Tools's default. Drop to 70 only if the file is still too big.
Resize before re-encoding
Re-encoding a 6000×4000 JPEG at quality 75 still leaves a huge file because of the pixel count. Downscale to the largest display size you need first — this multiplies the savings.
Don't re-compress repeatedly
JPEG is lossy, and every re-encode compounds artifacts (generation loss). Compress from the source once at the target quality. If you must re-compress, keep the original and start over rather than re-saving the compressed file.
When JPEG isn't the right output
If you want even smaller files and modern browser support is fine, switch the output to WebP or AVIF — both beat JPEG at equal visual quality. See converting to WebP.
Summary
Compress JPEG with MozJPEG at quality 75, resize first, and compress from the source once. You'll halve the file size with no visible loss — and switch to WebP/AVIF when you want the next level of savings.