4 ms·

This is neat, but it sure could use heck of a lot better index page. Here's an example of the output: http://www.patrickmeenan.com/progressive/view.php?img=htt

• Alupis 12y ago
  Can someone explain to a non-graphics person what this means? Seems like it's just demonstrating how the JPG get's displayed on your page while it's still being downloaded?
  • danbruc 12y ago
    The page just demonstrates that using progressive JPEGs yields a way better user experience than sequential ones. The page essentially turns an image into an animation simulating the loading behavior of both variants next to each other; while the progressive image is almost immediately completely visible (at low resolution) the sequential one builds up slowly from top to bottom.
    • thaumasiotes 12y ago
      Who says it's a better experience? I always think of progressive images as wasting resources by transmitting worthless information (the unintelligibile progressive image) along with the image I want to see. Text in a progressive jpeg tends to be a smear until you have the whole thing anyway.
      • danbruc 12y ago
        I am not completely sure without checking the specification but still pretty confident that progressive JPEGs are not made up of several images at different resolution but just have the low frequency component first. And images with text are neither the common use case for images nor the intended use case for progressive JPEGs.
        • thaumasiotes 12y ago
          The user experience is not determined by how the technology secretly works. Appearing to do something wrong is a bad thing in and of itself.
          • danbruc 12y ago
            I don't get it. Progressive JPEGs have no redundant information - I verified that - and are usually a bit smaller than sequential ones because of a more favorable arrangement of different components for entropy coding. And producing initially blurry images of text is not the fault of progressive JPEGs but at most a bad technology choice for a given use case. The image will get fully loaded in the same time no matter if it is sequentially or progressively encode so at best a sequential JPEG containing text can claim that the first lines get readable earlier.
      • bigiain 12y ago
        Except that the progressive image is delivering ~1000 _fewer_ bytes than the original (if my quick skim of the numbers is correct) - now I'm guessing that's because the original isn't particularly well optimised to start with, but I don't thing progressive jpegs in general add much to the payload size. It doesn't "transmit worthless information", it's more like it "re-orders the way it sends the information, so that even at only 10 or 20% loaded you get some very strong hints about the content."
      • pornel 12y ago
        There is no redundant information in progressive JPEG. JPEG stores image as frequencies (transforms 8x8 block into "layers" of varying levels of detail) and then it can arrange this data in the file in couple of ways, either: ABCD ABCD ABCD ABCD or AAAA BBBB CCCC DDDD
    • Scaevolus 12y ago
      Progressive JPEGs are also typically smaller than sequential ones, since they send equal-frequency components together in batches that compress better.
  • squeaky-clean 12y ago
    Yes, try using the slider to step through the animation. A progressive jpeg will load the whole image in a very low-resolution state and will progressively enhance the quality as it loads. A regular jpeg will just load vertically. You can see that at 50% downloaded the progressive image of Kermit looks good, certainly good enough for you to tell what the entire image is and be able to see some details. The non-progressive jpeg has half of it's image rendered, the other half still downloading.