Re: Canon 300D files contain 1MB EXIF headers?

Discussion in 'Digital Photography' started by Guido Vollbeding, Apr 1, 2004.

  1. Dave Martindale wrote:
    >
    > Ok. I think I see what you're saying. You end up reconstructing 4x4
    > blocks of the output image instead of 8x8 blocks, so the IDCTs are
    > cheaper. Right?


    Right.

    > I still don't see how you can avoid the Huffman
    > decoding of the 3/4 of the coefficients you're not going to use, since
    > they are all concatenated together in a stream. You can't discard them
    > until you've decoded the stream.


    You need to decode the symbol sizes (bit lengths), and can then drop (flush)
    the actual bits of unnecessary coefficients rather then grab the bits from
    the data stream and fully decoding, storing, and dequantizing them. I have
    done some actual timings and it *does* provide some marked speedup for the
    small downscaling values. (Perhaps I should add the results of actual
    timing tests below the given multiplication table...)

    The modified code has even less overhead for the variable range checks than
    the old one, because I need only one variable ("coef_limit") instead of two
    ("dc_needed" and "ac_needed" - the old code could only discard all AC
    coefficients together).

    For the details look in the provided source package, or quickly here:

    http://jpegclub.org/djpeg/jdhuff.c

    The efficient JPEG downscaling code seems to become popular, I have just
    found an acknowledgement here:

    http://www.fotana.com/main/product.html

    "Faster JPEG scaling, JPEGclub.org.
    This package uses some serious mathematical analysis to speed up scaling
    of JPEG photos during load. Fotana makes heavy use of downscaling since
    today's digital cameras take photos that are far larger than today's
    monitors (amazing!)."

    > Of course display speed matters. The problem with using progressive
    > JPEG is (a) some programs can't decode it correctly and (b) the files
    > are larger (though probably not as large as a non-progressive JPEG
    > plus an embedded half-size image).


    No, progressive JPEG files are usually *smaller* than sequential ones,
    at least when successive approximation is used (spectral selection alone
    may be slightly larger, but not significant).

    > I wouldn't be happy if my digicam
    > gave me JPEG images I couldn't read with some applications.
    > ...
    > Compared to you, of course. But why pick on Canon, who does basically
    > the same sort of processing as everyone else in-camera, and who manages
    > to produce images that look as good as any other Bayer camera
    > manufacturer?


    For what do they have their 'fabulous' "DIGIC" processor, then?
    It is only a piece of shit if they do such stupid and braindamaged
    things. And I think many users would agree with me that it is
    certainly better to have progressive JPEG than such stupid and
    braindamaged cripple. There are people screaming for completely
    incompatible JPEG2000, so why not use something which is already
    available and widely supported for years and which is capable
    to provide just the desired features (progressive JPEG)?

    > Why recommend Sigma, who alone among manufacturers can't
    > manage to produce JPEG images in camera? If anyone is less competent
    > in image processing, it's Sigma.


    The incompetence in image processing is common among digicam
    manufacturers, unfortunately. It was Foveon who also needed
    some support regarding basic decent JPEG application:

    http://jpegclub.org/foveon/

    But after all they listened and learned.
    The JPEG in camera thing is not important for Sigma, IMHO, because
    the current raw capture has important benefits compared with a direct
    JPEG capture. JPEG (at least the common 8-bit variant of it) is not
    appropriate for direct image capture, IMHO, I pfrefer the given raw
    route of Foveon and Sigma.

    Regards
    Guido
     
    Guido Vollbeding, Apr 1, 2004
    #1
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  2. Guido Vollbeding <> wrote in message news:<>...

    > The JPEG in camera thing is not important for Sigma, IMHO, because
    > the current raw capture has important benefits compared with a direct
    > JPEG capture. JPEG (at least the common 8-bit variant of it) is not
    > appropriate for direct image capture, IMHO, I pfrefer the given raw
    > route of Foveon and Sigma.



    The main problem with shooting RAW is that Canon and Fuji DSLRs don't
    provide a full resolution RAW preview on the LCD, only a tiny JPEG
    thumbnail. Better off shooting film.
     
    George Preddy, Apr 1, 2004
    #2
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  3. Guido Vollbeding

    John Navas Guest

    [POSTED TO rec.photo.digital - REPLY ON USENET PLEASE]

    In <> on Thu, 01 Apr 2004 11:26:00 +0200, Guido
    Vollbeding <> wrote:

    >The JPEG in camera thing is not important for Sigma, IMHO, because
    >the current raw capture has important benefits compared with a direct
    >JPEG capture. JPEG (at least the common 8-bit variant of it) is not
    >appropriate for direct image capture, IMHO, I pfrefer the given raw
    >route of Foveon and Sigma.


    Pretending that X3 drawbacks are actually advantages is kind of like trying to
    pretend that the lack of a rear view mirror in a car is a good thing because
    you can get a better view out the back by turning your head. ;-)

    --
    Best regards,
    John Navas
    [PLEASE NOTE: Ads belong *only* in rec.photo.marketplace.digital, as per
    <http://bobatkins.photo.net/info/charter.htm> <http://rpdfaq.50megs.com/>]
     
    John Navas, Apr 1, 2004
    #3
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