![]() ![]() With progressive JPEGs, you get a chance to see what the image is about much earlier and can either wait for it to fully load, or more likely just move on with your day without feeling like you’re missing out on anything. Their server is configured for slow delivery over the network to emulate poor network conditions. You can see this in action in your web browser with Pooya Karimian’s excellent baseline vs. The two image sequences below try to demonstrate the differences in the loading sequences (left-to-right) between the two profiles. ![]() You can see what the image is all about in a low resolution with details being added as they’re loaded. ![]() Progressive JPEGs also download top-to-bottom but is decoded in multiple passes adding more details in each pass. This requires you to have downloaded the entire image before you get to see it. Assuming they do and you want to test progressive JPEGs, check out this old, but still very relevant, post from Yahoo YSlow developer Stoyan Stefanov, who has some data on when, where and how to use progressive JPEGs.The JPEG image file format, one of the most common image formats on the web, can be encoded with one of two decoding profiles: baseline (sequential details) and progressive (additive details.) The latter variant offers many advantages on the web over the former variant especially for website visitors with low-bandwidth or high-latency.īaseline JPEGs load top-to bottom at full detail. First you should look at your site's stats, see which browser and devices your visitors are using and whether or not those browsers even render progressive JPEGs progressively. So, should you switch to progressive JPEGs? As with most things in web design there is no right answer. I suspect that how you feel about progressive JPEGs is probably, among other things, a good indicator of how long you've been using the web, which is to say that if you're all-too-familiar with progressive JPEGs from watching them slowly sharpen into focus over painfully slow dialup it's hard to see them as anything but an annoying anachronism. Unfortunately I haven't been able to find any actual usability studies addressing that question. That makes them potentially slower than baseline JPEGs in one of the use cases they're supposed to be ideal for – underpowered mobile devices.īut perhaps the most questionable aspect of progressive JPEGs is whether or not users actually perceive a fully loaded, but blurry image that eventually comes into focus as faster than an image that takes longer, but renders all at once. So while they may be marginally faster and possibly make users feel like the page has loaded faster, they hit the CPU pretty hard. All browsers will render progressive JPEGs just fine, but many of them – Safari, Mobile Safari, Opera and IE 8 – render progressive images just like baseline JPEGs, meaning there is no speed difference.Īnother strike against progressive JPEGs is that they must be rendered multiple times as more data arrives. With progressive JPEGs, because some data is loaded right off the bat, text doesn't jump around (you can avoid this for non-responsive images by specifying the image dimensions).īe sure to read Robson's full article for some important caveats regarding progressive JPEGs, including the fact that browser support is less than ideal. If you're building responsive websites, progressive JPEGs are also appealing because you can avoid the content reflow that happens when baseline images are loaded after text content.
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