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RE: [OM] fwd: Dodgital Cameras etc

Subject: RE: [OM] fwd: Dodgital Cameras etc
From: "Welliver, H William" <hwellive@xxxxxxxxxxxx>
Date: Wed, 5 Jul 2000 13:56:28 -0400
I'd just like to chime in regarding the JPEG/file resolution discussion (I
apologize in advance for extending this OT discussion):

I did a research project this past spring focusing on compression algorithms and
when one says that JPEG is a "mathematical" expression of an image is mostly
correct. When I think of mathematical representations of images, my thoughts
immediatly jump to vector image formats, which obviously JPEG is not. Baseline
JPEG uses the DCT (discrete cosine transform which is a linear transform akin to
the Fourier transform) to convert image data to a more compressible format. When
using a transform such as DCT, it is entirely possible to reduce image size far
beyond conventional compression algorithms even while being lossless. I do
believe that there is a "lossless" capability but that it's not frequently used
in JPEG. The compression ratios get even greater when you throw data away. The
next "big thing" in compression is wavelets, which should increase the
compression ratio while greatly reducing the artifacting associated with DCT
algorithms such as JPEG. 

If you're concerned about increasing image resolution without causing the
increase to make the image look terrible, I'd suggest looking into the Altamira
Group's nifty packages Genuine Fractals and Print Pro(?). They both use a
fractal image format that allows images to be manipulated in a lower resolution
and then be increased to the final output resolution while maintaining a very
high level of detail. It's great for enhancing the final resolution produced by
film scanners. In fact, I just read that Minolta will be bundling Genuine
Fractals with their new Scan Multi II multi format scanner.

As a final note, when I worked at a local newspaper a few years back, we mostly
used image resolutions of 200 dpi to print color spreads.

Bill

        -----Original Message-----
        From:   Tom Scales [SMTP:tscales@xxxxxxxxxxxxx]
        Sent:   Wednesday, July 05, 2000 11:50 AM
        To:     olympus@xxxxxxxxxxxxxxx
        Subject:        Re: [OM] fwd: Dodgital Cameras etc

        The key, I believe is whether you want a screen resolution (what you
were
        viewing) versus printing.  You need a heck of a lot more pixels to print
it
        in a quality that doesn't show the pixels.

        In my experience, with both an Alps Dye-sub printer and the Epson 1270
        printer, around 240dpi is required for a decent print.  I've read of
this as
        the magic number, and my experience has proven it to be true.

        Simple math for an 8 1/2 x 11 (what the sheets come in), says;

        8.5*240 = 2040
        11*240  = 2640

        For a 13x19, which I print a lot,

        13*240=3120
        19*240=4560

        So, for excellent 81/2x11 (or A4), the 2700 dpi scanners do a great job.
        For 13x19, a 4000dpi scanner makes a big difference.  The challenge for
the
        19inch dimension and a 2700 dpi scanner is 2700/19=142dpi, which is very
        marginal for the biggest prints.

        As for JPG, I don't believe it is a mathematical representation, but I
could
        be wrong. Regardless, it is lossy, so even the highest quality won't
match a
        TIF.  I scan 35mm negs into TIF, at around 62MB per TIF.  Even at 90%
        quality (which is very high), JPG's are around 6MB still.  Of course,
        resizing smaller and less quality for the web makes them manageable, but
not
        what I would print from.  Think about it, a 36 exposure roll, at 60Mb
per
        pic takes over 2GB.

        My thoughts.

        Tom



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