GoKawiilWhy JPEG XL Ignoring Bit Depth Is Genius (And Why AVIF Can’t Pull It Off)
People often ask me what I mean when I say “JPEG XL is simply the best thought out and forward thinking image formats there is. Nothing else is close.” This is article is just one example of why.
When I heard that JPEG XL’s encoder doesn’t care about bit depth, it sounded almost reckless (and I was downright confused). In a world obsessed with 8-bit, 10-bit, 12-bit precision wars, shouldn’t bit depth be fundamental? Isn’t more bits always better?
Here’s the twist: ignoring bit depth isn’t a limitation. It turns out it might be a brilliant design decision for modern image compression. And it reveals a fundamental philosophical difference between JPEG XL and AVIF that has massive implications for image quality, workflow simplicity, and future-proofing.
Let me explain why this ”non-feature’ is actually a superpower.
The Problem: Bit Depth Is Just a Convention, Not Reality
When Fractional first started building the JPEG XL community site, I ran tens-of-thousands of image tests for various parts of the site. I was really confused when I forced cjxl to limited outputs of 10- or 12-bits, and the resulting file was EXACTLY the same size. So much so, I reached out to Jon (the man leading the JPEG XL charge) to point out what was clearly a bug in the implementation). You can forgive me for being confused when he said it was the expected behaviour.
Inside JPEG XL’s lossy encoder, all image data becomes floating-point numbers between 0.0 and 1.0. Not integers. Not 8-bit values from 0-255. Just fractions of full intensity.
Whether your source was an 8-bit JPEG, a 10-bit camera RAW, a 16-bit professional scan, or even 32-bit floating point data, doesn’t matter. It all maps into the same [0, 1] range. The encoder sees the meaning of those colors, not how finely they were quantized before arrival.
Think about what this means: a bit is just a file format convention, not a perceptual reality.
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