> Note that it's generally not desirable to have FLIF used on the Web. A decent-quality JPEG will load at full resolution quicker than it takes FLIF to show a half-resolution preview.
On the other hand, this allows browsers on metered-bandwidth connections to control bandwidth more effectively. Rather than disabling images entirely, this would allow loading a low-resolution version and stopping, and letting the user control whether to load the rest of the image.
Again, this is not new in FLIF, and it isn't a strength of the format. You're describing exactly what can already be done with progressive JPEG better.
Truncated FLIF looks like a pixelated mess, whereas JPEG at the same byte size is almost like the original (note that the site has encoded JPEG to have few progressive scans, so sometimes you get half image perfect and half blocky. This is configurable in JPEG and could be equalized to entire image being ok-ish).
I wrote a Chrome plugin that does exactly this. I was living in an apartment with a heavily metered connection, and wanted a way to block large header images and 40mb GIFs. The extension let's you set a maximum image size, and uses the HTTP Range header to request only that much of the image - it's pretty naive but it works. Here is an example from Facebook, with the limit set to 10kB:
Unfortunately browsers don't do anything smart in terms of requesting progressive images, as there isn't an easy way to figure out how much of an image should be downloaded. So even on a 320x400px low end mobile device, you'll still end up downloading the whole the 2000x2000 header image - the only difference is it'll appear quicker as it is progressively rendered.
I would love to see this. Instead of network operators throttling bandwidth and/or re-compressing images, set a sane default and let the user have ultimate control.
On the other hand, this allows browsers on metered-bandwidth connections to control bandwidth more effectively. Rather than disabling images entirely, this would allow loading a low-resolution version and stopping, and letting the user control whether to load the rest of the image.