iOS Image Compression?

Discussion in 'iPhone' started by iStrat, Jul 4, 2010.

  1. iStrat macrumors member

    Joined:
    Jul 5, 2007
    Location:
    New York
    #1
    I never noticed this before, but iOS seems to compress images strangely when viewing them on the phone. I've been trying to make some nice looking wallpapers for the retina display, but the compression artifacts and resizing are annoying. If I lookup a nice hi-res image on Google Images, it's all blurry when I zoom in. Check it out with the sample below (5000x3750).

    http://www.psdgraphics.com/file/blue-sky.jpg

    On an actual computer, you can zoom in and read that text in the upper left corner. On the iPhone, if you zoom in on that text, it's all blurry. You're not getting the full resolution in Safari. If you save it to your phone, you can't zoom in all the way to read the text in the Photos app. If I zoom in with Dropbox, I can't zoom in all the way either, but it also seems blurry, like in Safari.

    So, I tried using photoshop to make a high quality 960x640 crop of a part of the image. That works and I can then zoom and see the text fine. However, there still seems to be bizarre compression artifacts. If I set the cropped image as my wallpaper, there is pixelation and blurriness around the clouds that I don't see when I look at it on my computer. Maybe iOS automatically reduces images down to 16-bit or 8-bit color (even though it should be able to handle 24-bit)? It looks more like compression artifacts than loss of color depth to me though. However, if you take a photo and sync it to your computer, it looks fine and is in full 32-bit, so it's only overly-compressed when viewed on the phone.

    Has anyone else noticed this? Am I crazy? Any workarounds? I want some really nice looking sharp wallpapers for the retina display. The built-in Wallpapers look fine somehow, but I'd like to add my own.
     
  2. iMacDragon macrumors 65816

    iMacDragon

    Joined:
    Oct 18, 2008
    Location:
    UK
    #2
    It's not the phone, its the mobile service providers, they tend to run a transparent proxy that recompresses jpeg's for smaller size to use less bandwidth. Sometimes this can be disabled with a specific APN setting, but usually you're at their mercy. reloading the page sometimes gets rid of it.

    You should notice them looking normal if you're on WIFI at home.
     
  3. iStrat thread starter macrumors member

    Joined:
    Jul 5, 2007
    Location:
    New York
    #3
    I don't think it's my ISP. I'm using WiFi in New York. Also, if I get the image onto my phone, then send it to my computer from there, it looks fine on the computer. No information is being lost. The images are being displayed improperly on the iPhone.

    Here is a comparison of the original cropped image I'm using as the wallpaper and a screenshot of how it appears on the phone. The difference is obvious. The iPhone wallpaper has much more compression on it.
     

    Attached Files:

  4. iMacDragon macrumors 65816

    iMacDragon

    Joined:
    Oct 18, 2008
    Location:
    UK
    #4
    HMm, ok, perhaps iOS is doing something too, then. But service providers certainly do muck about with jpegs frequently too, so that's got to be watched for, but sound like something else, you're right. looking at those shots, it doesn't look like compression, as such, it looks like the phone shot is at a much lower resolution for some reason.
     
  5. iStrat thread starter macrumors member

    Joined:
    Jul 5, 2007
    Location:
    New York
    #5
    The images are at the exact same resolution. You can see the clarity of the iOS components of the screenshot image (everything except for the wallpaper in the background). If you mean iOS may be reducing the resolution of the wallpaper, then that seems possible. Why would Apple do that though? And why don't I notice it on the stock wallpapers?
     
  6. iMacDragon macrumors 65816

    iMacDragon

    Joined:
    Oct 18, 2008
    Location:
    UK
    #6
    yes, I meant the wallpaper itself appears to be at a lower than actual pixel resolution, not the screenshot itself. If anything, I'd suspect the wallpaper looks to be sized for 3Gs, but displayed by 4 leading it to be 1/4 the pixels it should be. Could be a bug along those lines perhaps.


    try uploading your pc snapshot to the phone and setting that as wallpaper, see if it then appears full resolution?
     
  7. iStrat thread starter macrumors member

    Joined:
    Jul 5, 2007
    Location:
    New York
    #7
    Okay. Nevermind. The Dropbox app is compressing the image or reducing the resolution I think. I threw it on the web and downloaded it from there and it looks fine now.
     

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