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General expectations for PDF file size

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  • #16
    Originally posted by Dov Isaacs View Post

    The “automatic” aspect of this is that we examine each image as we produce and export the PDF file. If the image is “vector-like” we compress with lossless ZIP compression, avoiding those nasty JPEG imaging artifacts and lossiness. If the image is photographic (i.e., something that would typically come out of camera), we apply JPEG compression at the special quality setting.

    - Dov
    That's interesting. How does the software know what type the image is? Image analysis? Number of unique colors in the image, sharpness of edges or something similar?

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    • #17
      Originally posted by Schnitzel View Post

      That's interesting. How does the software know what type the image is? Image analysis? Number of unique colors in the image, sharpness of edges or something similar?
      It carefully analyzes the image and works exceptionally well. The code exists not only in PDF export/save from InDesign and Illustrator, but also in the Distiller in converting PostScript to PDF!

      - Dov

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      • #18
        Originally posted by Dov Isaacs View Post

        Whereas I would agree with you wrt/ how inexpensive disk space is and per my posting wrt/ resampling I would avoid cascading rounds of decompression, downsampling, recompression - especially with JPEG, JPEG compression at maximum quality is generally not a problem for photographic types of images and reasonably high resolution. Raster images of what would probably have been better represented as either text or vector images should never be JPEG-compressed. ZIP compression is much more appropriate and lossless.

        In Adobe applications such as InDesign and Illustrator, you should use the “Automatic (JPEG)” at “Maximum Quality” for images. Why? The “automatic” aspect of this is that we examine each image as we produce and export the PDF file. If the image is “vector-like” we compress with lossless ZIP compression, avoiding those nasty JPEG imaging artifacts and lossiness. If the image is photographic (i.e., something that would typically come out of camera), we apply JPEG compression at the special quality setting. For the vast majority of printing applications, this works out without any perceptible quality loss. (BTW, unless your image workflow uses RAW images followed by use of TIFF or PSD subsequently as opposed to out-of-camera JPEG, you have already suffered through a round of image lossiness!)

        - Dov
        Agreed. For the vast majority...which is why I prefer to use ZIP because it always works without any quality loss.
        Joe
        OS: Mac OS X 10.10.2 - RIP: Prinergy Connect 6.1 - CTP: Luscher XPose! 160 (2)

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        • #19
          Originally posted by Repro_Pro View Post
          Whenever we produce a PDF that seem abnormally large, we re-save that PDF using Acrobat (no change to any parameter).
          In many cases the new PDF file size diminishes significantly.
          I have no idea why this happens.
          One reason is,
          because: If you re-save (with "save as") you kill the history of changings in a document. Only the latest, actual state of the document will be written.

          An other reason for unnecessary growing of a PDF-file coud be: Depending from the Export Settings sometimes much to much icc-profiles (each about 1-2 MB) were added to objects. For an example PDF/x-3 add (often) the same CMYK-profile to former not calibrated pictures and text aditional to the Output intent… ;-)

          Ulrich

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          • #20
            Thanks Ulrich,
            But, if Illustrator saves history inside the pdf and that info is not available to us, then such behavior is clearly counter-productive.
            Beyond that, why would Acrobat strip any info "silently" when a file is simply saved AS IS?
            BTW, I believe Acrobat doesn't strip the native Illustrators' file structure, that we actually want to keep.
            I wonder if Acrobat is actually re-structuring the Illustrators' pdf internal file structure and optimizing it?
            Perhaps Dov can shed some light here...

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