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    Picture sizes

    I have recently upgraded my Mac OS X operating system version to 10.4.10 on my Mac PowerBook G4 15", and this has upgraded the version of the utility Preview which I habitually use to view picture sets to Preview 3.0.9. This has made me notice a minor "problem" with some sets.

    In Preview I use the tool "View at actual size". For most picture sets this fills my screen (and a little bit more) with a landscape picture - I reckon it's one bit per pixel.

    In the sets in Jorinel-Small, the picture "Viewed at actual size" occupies about a third of the screen (perhaps a touch more) in each direction.

    I have found that this is due to the is due to the Density values in the JFIF (JPEG File Interchange Format). Bytes 14 to 18 code as follows:

    14: units (1 byte) Units for the X and Y densities.
    _____ units = 0: no units, X and Y specify the pixel aspect ratio
    _____ units = 1: X and Y are dots per inch
    _____ units = 2: X and Y are dots per cm
    15+16: Xdensity (2 bytes) Horizontal pixel density
    17+18: Ydensity (2 bytes) Vertical pixel density

    So if these bytes of each JPEG were changed from

    01 01 2C 01 2C to
    00 00 64 00 64

    Density would change from "300 dpi" to "pixel aspect ratio". This makes the pictures work in the same way as the vast majority of the pictures on the site.

    In the sets in Jorinel-Big I can only see a small portion of the picture when "Viewed at actual size", and the result is pixelated. The above manipulation has no effect.

    Any experts out there who can tell me what's going on?

    The attached images show what I see with picture viewed at "full size", with an actual size clip of the d_vanessa one to show the pixelation.
    Attached Files
    Last edited by Jorinel; 29 November 2007, 01:29 PM. Reason: spelling

    #2
    I get the same effects on Tiger with Preview 3.0.9 but it works OK in Leopard with Preview 4.0.0

    I don't have an explanation but it looks like a Preview problem?

    It's not an effect I would notice because I view photos in iPhoto or Xee.

    L

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      #3
      Hi Lesley

      Thanks for your input. I'm glad i'm not just seeing things.

      I haven't come across Xee before - it looks like just what I need.

      Jorinel

      Comment


        #4
        I like Xee, it's just so easy to use.

        Sometimes less is more, much more!

        L

        Comment

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