I know this might get closed as too subjective, but let's give it a shot as it's probably relevant to a lot of Magento stores out there and given a certain set of constraints, there is probably a reasonably clear answer as to the best overall solution.
I'm wondering whether it's a good idea to use transparent PNGs for product shots instead of JPGs. I've read (https://stackoverflow.com/a/7752936/1117286) that PNG-24 file size can be as much as 5X that of a similarly compressed JPG file, but I'm not sure if that figure is accurate or up-to-date with current compression tools out there.
Obviously for a merchant that can place products against a white background and doesn't plan on changing that any time soon, JPGs would make a lot more sense.
In our case, we have some product shots that are against a textured background and others that are against a white background. The product shots that are against a textured background we just use one gigantic image for the whole thing.
So there would be a clear benefit to transparent PNGs in those cases. And even for the other images that are currently against a white background, we may want to place them also against a textured background at some point in the future - so transparent PNGs would give us some nice future-proofing.
We're also responsive and we get a fair amount of mobile traffic, so we want to keep that in mind.
Given this set of constraints, is using transparent PNGs a reasonable solution? I've yet to find any eCommerce sites out there using transparent PNGs, would be interesting if anyone could post links to them.