Compress without losing quality.

Lossless: the same pixels

The resulting image is identical, pixel for pixel. It's what you want for screenshots, logos and graphics. In our tests with that kind of image, optimizing the PNG with OxiPNG saves 33%, and turning it into lossless WebP, 62%.

With photos, lossless savings are small. The exception: a JPEG you already have can be turned into JPEG XL without losing anything, and it weighs quite a bit less.

Optimized PNG, like oxipng

$ apolo png -o 4 screenshot.png

Lossless WebP

$ apolo webp -lossless -z 9 screenshot.png -o screenshot.webp

With a loss you can't see

Photos compress much further if you accept losing detail the eye doesn't notice. At a SSIMULACRA 2 score of 90, which you can't tell apart even up close, our 24 photos weigh 79% less in JPEG XL and 77% less in AVIF than the original PNG.

How to know it doesn't show

Apolo measures each result with SSIMULACRA 2, the perceived-quality metric from the JPEG XL project: at 90 or more you can't tell them apart; at 70, it's high quality; at 50, it shows. And it shows the original and the result with a slider, side by side or with a difference map.

Instead of trying qualities blindly, you can ask for the score: “Quality by score” finds, photo by photo, the lowest quality that reaches it.

A folder, without it showing even up close

$ apolo lote photos/ --formato avif --objetivo 90

Measure a result against its original

$ apolo medir photo.png photo.avif

And the size

What usually weighs most in a photo is that it's bigger than it will be seen. A 4000-pixel phone photo shown at 1200 carries eleven times more pixels than needed. Apolo shrinks it to the longest side you ask for before compressing.

$ apolo lote photos/ --formato avif --objetivo 90 --lado-mayor 2400