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    Re: I SAY AGAIN -- Re: ADMIN: attachments: pdf vs jpgand others
    From: Frank Reed
    Date: 2013 Apr 23, 18:31 -0700

    First, I apologize if anyone is getting annoyed by this off-topic thread.

    Regarding jpg's versus pdf's, I had forgotten about one extra issue which also CAN make pdf's smaller --though it's no guarantee. The primary, preferred internal image format in the pdf file was changed a couple of years ago to jpeg2000 which is indeed more efficient than jpeg but still usually requires a "quality" change. This is entirely dependent on the default settings in the pdf creation software. Since pdf is not an image format, software that creates pdfs from images can do so in a broad variety of ways. This is not dependable behavior.

    The case that Antoine posted is what I would call a pathological example (not intentionally, of course!). Hand-drawn diagrams can become enormous when they are scanned. You can write "1+1=2" three inches tall on a normal piece of paper, and when it's scanned that very small amount of information gets converted into the equivalent of a grand landscape painting displaying every little smudge on the page and every subtle change in ink intensity. It's 99.9% noise and 0.1% message. Stored as a jpg, we get the worst of all possible worlds. The sharp "edges" in hand-drawn diagrams and text are terrible for the jpg algorithm and they generate those annoying jpg "artifacts" that look like diffraction rings around the drawing's elements. Any processing after that will usually reduce the file size, sometimes dramatically, and also reduce the artifacts, and running it through a pdf packaging process may very well reduce the file size. This is a loss in "quality" of the photograph of the page which does nothing to damage the information content (it still says "1+1=2"). But there are many ways to achieve the same improvement and more: reduce overall image width and height, reduce color depth, apply a smoothing or "blurring" filter, and then save as a png.

    Finally, the issue of file size is no longer a significant concern for NavList messages. I have dealt with that behind the scenes, and you don't have to think about it... within reason! So please, just go with what I said in the original "ADMIN" post, ok? Single images and small sets of images should be posted as image files (jpg or png preferred), and pdf should be reserved for complex documents.


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