EOS20D CR2 format and camera settings

Discussion in 'Digital SLR' started by Jim Garrison, Dec 11, 2005.

  1. Jim Garrison

    Jim Garrison Guest

    I understand that 'raw' format is supposed be just that:
    48bpp of the raw levels recorded by the camera sensor,
    totally unprocessed.

    However, the ISO setting obviously affects the captured
    data, so *some* processing is going on, even with
    raw files.

    What I'm looking for (if it exists) is a chart showing
    which camera settings actually affect the raw numbers in
    some way, and which are stored as metadata.

    My guess is that the ISO setting results in different levels
    of amplitude scaling, but all other image settings (WB, color
    space, contrast, sharpness, saturation and color tone) are
    merely recorded as metadata in a .CR2 file and don't change
    the recorded pixel values.

    Jim Garrison, Dec 11, 2005
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  2. Jim Garrison

    Scott W Guest

    The camera changes its analog gain stages when you change the iso. I
    believe that is the only setting that will affect the raw data, other
    then thing like sutter speed.

    Scott W, Dec 11, 2005
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  3. $I understand that 'raw' format is supposed be just that:
    $48bpp of the raw levels recorded by the camera sensor,
    $totally unprocessed.

    36, actually; the sensor works at 12 bits.

    $However, the ISO setting obviously affects the captured
    $data, so *some* processing is going on, even with
    $raw files.

    ISO is analog, controlled by the gain level of the amplifiers on
    the chip. Some sources claim that 3200 is actually the same as
    1600 but with digital modification; Canon, to the best of my
    knowledge, has never released a statement about whether or not
    this is the case.[/QUOTE]
    Stephen M. Dunn, Dec 11, 2005
  4. Jim Garrison

    JPS Guest

    In message <ihPmf.43077$>,
    Unfortunately, the RAW data is actually only 12-bit for most DSLRs. It
    is a 12-bit value that more or less represents the amount of charge in
    the cells, in a linear proportion. Not totally true, however, as the
    data is offset on many cameras (black is much higher than 0 in the RAW
    For most ISOs, the number is proportional to the amplification used
    before converting the signals to numbers. Cameras may use
    multiplication of under-exposed data instead of purely amplification for
    their highest ISO(s). The Canon 20D's ISO 3200 is really 1600 with the
    RAW numbers doubled, and a stop of under-exposure; not very useful if
    you shoot RAW, as setting the camera to ISO 1600 and -1 EC yourself will
    leave you a stop of headroom that is clipped when the camera is set to
    ISO 3200.
    Pretty much. At any given ISO, the only factors that affect the RAW
    data directly are the shutter speed and the f-stop, and the amount of
    light coming through the lens. All those other things are just
    metadata. There are possibly some exceptions, however; at least one
    DSLR (Nikon D2X) purports to use the WB setting so that the red and blue
    channels have independent amplification, and therefore, virtually
    independent ISO.
    JPS, Dec 11, 2005
  5. Jim Garrison

    JPS Guest

    In message <>,
    It doesn't matter what Canon says; the RAW data has no unique
    information for the least significant bit in the top 1 or 2 ISOs on the
    Canon cameras. The 20D has all even numbers at ISO 3200 in the RAW
    data, except for a few hundred bad pixels that are odd when averaged
    from their neighbors. The 10D has patterns of 1s and 0s in the least
    significant bit that are not possibly the real digitized data, at ISOs
    1600 and 3200:


    JPS, Dec 11, 2005
  6. Jim Garrison

    JPS Guest

    I forgot to mention why it is only 12-bits. Each pixel only measures
    one color band, red, green, or blue, depending on the filter over it.
    The filters are over the pixels in a pattern like this:

    R G R G R G

    G B G B G B

    R G R G R G

    G B G B G B

    R G R G R G

    G B G B G B

    The full RGB pixels are generally derived from the RAW data by a type of
    interpolation called "demosaicing".
    JPS, Dec 11, 2005
  7. Jim Garrison

    Jim Garrison Guest

    Thanks! That was more than I asked for, but just what
    I needed to know.

    Jim Garrison, Dec 11, 2005
  8. Jim Garrison

    Paul Furman Guest

    Ah, that's the same WB setting that caused the encryption controversy,
    thanks for clarifying.

    On a similar note, color filters (or polarizer, etc.) on the front of
    the lens are another way to change the raw data.
    Paul Furman, Dec 12, 2005
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