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Re: Lossless JPEG

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  • pauldavidbourke
    ... they may, change over time. I think many of us know that JPG is compressed and is lossy. Here are some thoughts along those lines ... quality of it. So,
    Message 1 of 6 , Sep 22, 2005
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      > Most of you might know that I am an advocate for JPG, at this time. Opinions be what
      they may, change over time. I think many of us know that JPG is compressed and is lossy.
      Here are some thoughts along those lines
      > "baseline JPEG is lossy because it is subject to roundoff errors in various calculations."
      > The compress and re-compress of a JPG is known as something that degrades the
      quality of it. So, then the final dome masters are what you make as JPG's. These are the
      frames that aren't going to get editing any further. Produce the show with high quality
      standards and files then PRINT it to JPG's.

      This is not necessarily the forum for a discussion on this but may I make a few comments.

      First, it is true that baseline JPEG is always lossy.

      However the ISO standard DOES describe a lossless JPEG, that is, mathematically pixel
      perfect lossless, not just perceptual lossless.

      There is also "JPEG-LS" which is a lossless JPEG standard being used increasingly.

      So as far as I am aware, the maximum quality quality setting in the Mac version (perhaps
      others) of PhotoShop is implemented as lossless JPEG.

      As far as personal opinions/recommendations are concerned, I would suggest PNG as a far
      superior fomat.
    • Ryan Wyatt
      ... N.B. that this does not give the kind of compression ratios that JPEG admirers so deeply desire. More like 2:1 than 10:1. ... I know that JPEG-LS requires
      Message 2 of 6 , Sep 22, 2005
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        > However the ISO standard DOES describe a lossless JPEG, that is,
        > mathematically pixel perfect lossless, not just perceptual lossless.

        N.B. that this does not give the kind of compression ratios that JPEG
        admirers so deeply desire. More like 2:1 than 10:1.

        > There is also "JPEG-LS" which is a lossless JPEG standard being
        > used increasingly.

        I know that JPEG-LS requires a special plug-in for Photoshop, which
        rather makes me doubt the following:

        > So as far as I am aware, the maximum quality quality setting in the
        > Mac version (perhaps others) of PhotoShop is implemented as
        > lossless JPEG.

        Adobe doesn't make this claim anywhere that I can find. It seems
        like they'd tell us if that were the case, doesn't it? The online
        manual has this to say:

        "JPEG (Joint Photographic Experts Group)

        "Lossy compression; supported by JPEG, TIFF, PDF, and PostScript
        language file formats. Recommended for continuous-tone images, such
        as photographs. To specify image quality, choose an option from the
        Quality menu, drag the Quality pop-up slider, or enter a value
        between 0 and 13 in the Quality text box. For the best printed
        results, choose maximum-quality compression. JPEG files can be
        printed only on Level 2 (or later) PostScript printers and may not
        separate into individual plates."

        It would have been easy to mention that "13" is lossless, right?
        I've looked on online forums, in their support pages, etc., but I see
        nothing to support the claim that the highest setting is lossless.
        I'd appreciate it if one of the many people making this claim would
        provide supportive documentation. (Sorry, this is getting to be a
        sore spot with me.)

        My biggest concerns with JPEG are color and geometry. As I
        understand it, most JPEG compression schemes start off with an
        immediate conversion to YCbCr, which gives you even less color range
        than 8-bit, I believe, and further steps in this process knock the
        color space down even further: with new display systems, we need to
        be moving toward increased color depth, not less. As far as geometry
        goes, everybody knows JPEG has problems with rotations, resampling,
        and recompression, and that's exactly what we're doing when we put
        dome masters onto a multi-projector system: we rotate the image to
        match the projector position, resample it to match the geometry, then
        (typically) recompress it to get it to play back.

        Can anyone think of a way to do a side-by-side JPEG versus
        uncompressed test? Maybe just on two adjacent channels of a multi-
        pipe system...?

        BTW, I'm not saying we should leave JPEG out of the draft standard,
        but I think we need to describe the pluses and minuses as clearly as
        possible.

        A somewhat amusing anecdote: you can see JPEG artifacts rendered in
        bronze (I think it's bronze) at the Rose Center! We have a
        topographic moon globe based on Don Davis's exhaustive mapping of the
        lunar surface. To create the globe, a greyscale bumpmap of Don's was
        used to yield the topology of the surface. Don provided an
        uncompressed image, but at some point, an exhibit fabricator or
        *someone* put the image through a JPEG compression that left
        significant artifacts. Because theses artifacts were then used to
        create the texture of the bronze globe, you can run your fingers
        across little rectangular bumps that correspond to the way the image
        was broken up and compressed by the JPEG routine. Sad, but true.

        > As far as personal opinions/recommendations are concerned, I would
        > suggest PNG as a far superior format.

        Out of curiosity, does PNG experience orientation problems (e.g.,
        like TIFF, which defines orientation in a header that not all
        programs recognize)?

        More importantly, however, I don't believe that PNG appears in the
        current draft of the dome master standard; we should add it.


        Ryan, a.k.a.
        Ryan Wyatt, Science Visualizer
        Rose Center for Earth & Space
        American Museum of Natural History
        79th Street & Central Park West
        New York, NY 10024
        212.313.7903 vox
        212.313.7868 fax
      • Paul Bourke
        ... And I m not claiming that, just what I ve been told. If I want to save images in a lossless way I will do so using a format specifically designed for that,
        Message 3 of 6 , Sep 22, 2005
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          > > So as far as I am aware, the maximum quality quality setting in the
          > > Mac version (perhaps others) of PhotoShop is implemented as
          > > lossless JPEG.
          > Adobe doesn't make this claim anywhere that I can find. It seems
          > like they'd tell us if that were the case, doesn't it? The online
          > manual has this to say:

          And I'm not claiming that, just what I've been told. If I want to save
          images in a lossless way I will do so using a format specifically
          designed for that, not JPEG.

          > My biggest concerns with JPEG are color and geometry.
          > BTW, I'm not saying we should leave JPEG out of the draft standard,
          > but I think we need to describe the pluses and minuses as clearly as
          > possible.

          I haven't really contributed to the full dome standards business so am
          not sure where file formats come in. As a practical matter I assume
          (hope) full dome members aren't using JPEG as the storage format for
          movies. There's a big difference between using such a format for the
          final playback format (we use PhotoJPEG for our QuickTime movie codec)
          compared to the archive format of the original frames.

          > > As far as personal opinions/recommendations are concerned, I would
          > > suggest PNG as a far superior format.
          > Out of curiosity, does PNG experience orientation problems (e.g.,
          > like TIFF, which defines orientation in a header that not all
          > programs recognize)?

          Ahhh, the old problem of standards that aren't supported properly in
          software. I can't vouch for PNG support across a wide range of
          software, especially since I rarely use MSWindows. I do know TIFF
          support under MSWindows can be poor, many applications use libraries
          that don't even handle the big and small endian information in the
          TIFF file header.

          The relative merits of PNG
          - A freely available reading/writing library supplied as source code.
          - 9 bit alpha channels (not so amazing).
          - Gamma correction support (important).
          - Up to 48 bit colour and 16bit grey (16 bits per RGB, interestng for
          large dynamic range in domes).
          - Doesn't allow vendor specific tags (biggest headache with TIFF).
          - Good lossless compression (often much better than TIFF).
          - Patent free, by design.

          Having said all that, I use gzipped TGA files for original frames and
          playback using "high" quality PhotoJPEG.

          --
          P a u l B o u r k e
          Email: paul.bourke@...
          http://astronomy.swin.edu.au/~pbourke/
        • slevy@new.math.uiuc.edu
          ... How about blink-comparison? A severe test would be to use a lossless path to transport, say, even-numbered dome master frames, and a high-quality JPEG
          Message 4 of 6 , Sep 23, 2005
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            Ryan Wyatt wrote:

            > Can anyone think of a way to do a side-by-side JPEG versus
            > uncompressed test? Maybe just on two adjacent channels of a multi-
            > pipe system...?

            How about blink-comparison? A severe test would be to use a
            lossless path to transport, say, even-numbered dome master frames,
            and a high-quality JPEG path to transport odd-numbered frames,
            on a single scene; then split each per projector and project the results.
            Differences would show up as shimmering.

            I haven't tried the above, but regularly do blink-comparison of single
            frames to test JPEG visual quality. The results do depend on the display
            system, and they're certainly more likely to show up on scenes with extended
            areas of very low but nonzero brightness; still I've almost never
            managed to notice a difference between 98-100% JPEGs and lossless paths.
            On the other hand, our displays take only 8-bit data.

            I'd be interested in others' reports on tests like these...

            Stuart Levy, slevy@... (& at new.math...)
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