image quality limitation on iPhone

palmoufpalmouf
Posted:
in iPhone edited January 2014
Hi,



I am a big fan of a french comic blog which I am looking at through my iPhone.

but for strange reasons some notes are readable, and others are not due to the iphone jpeg rendering i believe.



When the comic is composed a a single image that is more than 2800 px height (for a width of 765) the jpeg seems to be loaded in much lower quality.



zoomed part of the image which is more than 2800 px height





zoomed part of the image wich I cut to be less than 2800 px height





does someone has any clue about this ?



link to the mobile version of the blog I am following



link to another image I found on the internet with the same behaviour have a llok at it on a desktop and then on the iphone, and look at the text quality is also reduced drastically in the same way

Comments

  • Reply 1 of 4
    MarvinMarvin Posts: 15,326moderator
    Yeah, I get this sort of thing too on my iPhone - mine even seems to crop some large images. It's the 3G provider trying to save bandwidth. If you close the site down and go into settings > safari > clear cache and then open the same site after connecting to wifi, the images should be the originals.



    It makes you grudge paying so much for data access everywhere. Faster loading times will be preferred in most cases but if I specifically want to look at images and only 3G is available, I'd rather they weren't blocky.



    The sooner we get 4G or LTE everywhere the better.
  • Reply 2 of 4
    dfilerdfiler Posts: 3,420member
    Looks like the image is only partially loaded for whatever reason. The newer jpeg implementations deliver every other line first and then the missing lines. This was incredibly useful in the analog modem era. It allowed images to be displayed (in a useable manner) while loading. (this description is admittedly a drastic simplification)



    My guess is that the image is only partially laded due to the imense dimensions.
  • Reply 3 of 4
    palmoufpalmouf Posts: 4member
    Quote:
    Originally Posted by dfiler View Post


    Looks like the image is only partially loaded for whatever reason. The newer jpeg implementations deliver every other line first and then the missing lines. This was incredibly useful in the analog modem era. It allowed images to be displayed (in a useable manner) while loading. (this description is admittedly a drastic simplification)



    My guess is that the image is only partially laded due to the imense dimensions.



    Hi dFiler,

    You found it right, i just have seen in following document:

    http://developer.apple.com/safari/li...ioniPhone.html



    which explains

    Quote:

    JPEG images can be up to 32 megapixels due to subsampling, which allows JPEG images to decode to a size that has one sixteenth the number of pixels. JPEG images larger than 2 megapixels are subsampled?that is, decoded to a reduced size. JPEG subsampling allows the user to view images from the latest digital cameras.



    Thanks for your help
  • Reply 4 of 4
    carniphagecarniphage Posts: 1,984member
    Quote:
    Originally Posted by palmouf View Post


    Hi,



    I am a big fan of a french comic blog which I am looking at through my iPhone.

    but for strange reasons some notes are readable, and others are not due to the iphone jpeg rendering i believe.



    When the comic is composed a a single image that is more than 2800 px height (for a width of 765) the jpeg seems to be loaded in much lower quality.




    I suspect that the graphics hardware has a maximum texture size of 2048 pixels in any one dimension.



    The iPad seems to have 4096 pixels as a maximum dimension.



    Larger images are down-sampled which then causes blurriness.



    C.
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