Comment by PunchyHamster
24 days ago
> Maybe a lossless re-encoding of my website JPEGs to gain 20% size is not worth the 33% longer decode,
And pray tell how much of the waiting for page is used on decoding image (vs transferring) and how much faster the image gets on the machine when it's 20% smaller on average connection?
My guess is that time saving from bandwidth decrease more than compensates for that
Well it obviously depends on the connection, but at 3g speeds and higher, the decoding time outweighs the fairly minor bandwidth saving.
And if you're displaying a cached image, the bandwidth use is zero, but the decoding still happens.
> And if you're displaying a cached image, the bandwidth use is zero [...]
But then less stuff fits in my cache, so I'm transferring even more data.
Also, not everybody has unlimited/unthrottled data plans. I really wish websites would respect my resource tradeoff preferences at least somewhat.
I dont know how you calculate that, but for my phone I get the payoff (given a 30% size reduction) to be positive below anywhere from 30-43Mbps.
When on celular, even 5g, I am pretty often below that.
https://random-stuff.jakearchibald.com/apps/img-decode-bench...
Taking bike.jpg and bike-repackaged.jxl in that demo, on my Pixel 10 Pro in Firefox Nightly, the size and decoding times are:
bike.jpg - 147 kB - 10ms
bike-repackaged.jxl - 126 kB - 33ms
So, I save 21 kB, but pay 23ms.
That extra 21 kB isn't part of a new request, so when it comes to download performance, we're talking about an active response. At 3g speeds, in 23 ms you can download somewhere between 20-118 kB, so at best, it evens out.
If it's a lower end device, the decode delta increases. If it's a faster connection, the 21 kB saving matters less. If the image was cached, then I'm just paying the decode overhead.
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It depends on your network speed, how big the image is, the compression rate of the image, and how fast your hardware is.