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Comment by jaffathecake | Hacker News Reader

Those images are displayed at the correct size for high density devices. Real users don't zoom in and compare to the original.

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The file sizes quoted should be for the resolution of image actually displayed. It would be fine to say a 960x540 image is X bytes with AVIF and Y bytes with JPEG and let viewers judge for themselves whether the two look equivalent. What that page actually does is quote the file sizes for 1920x1080 images, but shrink them to 960x540 before letting viewers compare the compression quality.

That's how you cater for high density devices.

If you take a 320x image and display it at 320x CSS pixels, it'll look blurry on the vast majority of mobile devices, and a lot of laptops, because 1 CSS pixel is larger than 1 device pixel.

https://developer.mozilla.org/en-US/docs/Web/API/Window/devi...

Fwiw this is covered in the article https://jakearchibald.com/2020/avif-has-landed/#what-is-acce...

Are you saying that people don't ever zoom in on images on the web? Because my wife does this regularly to look at details in photos.

I'm saying it's an edge case you shouldn't optimise for. Otherwise, if you're displaying an image at 640x480 CSS pixels, how wide should the image be in pixels? 2,000? 3,000? 10,000? Maybe each image should be 10MB just in case the user zooms in that far?

I think you should optimise for regular display size and density.

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