4 ms·

One thing that hasn't been addressed is the cost of making the second image request. There is probably a break even point for this technique where it becomes us

One thing that hasn't been addressed is the cost of making the second image request. There is probably a break even point for this technique where it becomes useful, but the added complexity greatly limits its utility.

pyre 16y ago
> In one case we got a 573KB 24-bit PNG down to a > 49KB JPEG with a 4KB PNG alpha-mask! I somehow don't think that the cost of using two requests vs just one really matters with that kind of size difference (unless you're serving high-latency customers on satellite internet or something).
- nathanhammond 16y ago
  That would certainly be beyond the break even point. :) In that case it's definitely another tool to keep in the back pocket in case needed. (Somehow I missed that line in the article by focusing in on the code.)
  - mthoms 16y ago
    Could also use a data uri for the mask if a second request is really an issue.
- masklinn 16y ago
  > I somehow don't think that the cost of using two requests vs just one really matters with that kind of size difference On DSL it probably doesn't (let's consider a 150ms ping, we'll take that as the time to initiate an HTTP connection, with 10Mbps of bandwidth or 1.25MB/s): the single image will take 150ms + 440ms (download) for a total of 590ms, whereas the pair will take 2x150ms + 40ms + 3ms for a total of 343ms. Now consider 3G: 3.6Mbps (460KB/s) (we'll consider a pretty basic HSDPA) and pings of around 600ms are common. The single image takes 600ms + 1246ms for a total of 1846ms, whereas the pair takes 2x600ms + 100ms + 9ms for a total of 1309ms. Still lower, but we're getting closer. 7.2Mbps HSDPA bumps the bandwidth to 920KB/s and doesn't change the ping significantly. Now the single image only takes 632ms to download for a total of 1232ms, and the pair takes 54ms for a total of 1254ms. And cell data usage will only grow further. Now of course, a 573KB full-color PNG is going to be hell on a mobile browser and its cache, but still, HTTP request cost is coming back with a vengeance as HSPA makes high amounts of bandwidth available.

pyre 16y ago

> In one case we got a 573KB 24-bit PNG down to a > 49KB JPEG with a 4KB PNG alpha-mask! I somehow don't think that the cost of using two requests vs just one really matters with that kind of size difference (unless you're serving high-latency customers on satellite internet or something).

nathanhammond 16y ago
That would certainly be beyond the break even point. :) In that case it's definitely another tool to keep in the back pocket in case needed. (Somehow I missed that line in the article by focusing in on the code.)
- mthoms 16y ago
  Could also use a data uri for the mask if a second request is really an issue.
masklinn 16y ago
> I somehow don't think that the cost of using two requests vs just one really matters with that kind of size difference On DSL it probably doesn't (let's consider a 150ms ping, we'll take that as the time to initiate an HTTP connection, with 10Mbps of bandwidth or 1.25MB/s): the single image will take 150ms + 440ms (download) for a total of 590ms, whereas the pair will take 2x150ms + 40ms + 3ms for a total of 343ms. Now consider 3G: 3.6Mbps (460KB/s) (we'll consider a pretty basic HSDPA) and pings of around 600ms are common. The single image takes 600ms + 1246ms for a total of 1846ms, whereas the pair takes 2x600ms + 100ms + 9ms for a total of 1309ms. Still lower, but we're getting closer. 7.2Mbps HSDPA bumps the bandwidth to 920KB/s and doesn't change the ping significantly. Now the single image only takes 632ms to download for a total of 1232ms, and the pair takes 54ms for a total of 1254ms. And cell data usage will only grow further. Now of course, a 573KB full-color PNG is going to be hell on a mobile browser and its cache, but still, HTTP request cost is coming back with a vengeance as HSPA makes high amounts of bandwidth available.