10D ISO 1600 is pushed one stop from 800

Discussion in 'Digital SLR' started by JPS, Dec 30, 2004.

  1. JPS

    JPS Guest

    I just took blackframe and super-overexposed white wall images at ISOs
    800, 1600, and 3200 on my 10D. I converted them all to uncompressed DNG
    files, and looked at the RAW data in a hex editor (set to look at the
    data as decimal numbers, assuming 16-bit unsigned data). The data
    patterns are the same for the 1600 and 3200, and both are a little
    strange. You get a long string of even numbers, then a long string of
    perfectly alternating odd and even numbers, then a long string of odd
    numbers, then a long string of alternating numbers again. I don't know
    if it's the camera or the DNG converter that is doing this to the data
    (adding or subtracting one to blocks and striped blocks), but it's quite
    clear that there are only 11 bits used for both ISO 3200 *AND* ISO 1600.
    Here is some sample data from the ISO 1600 blackframe:


    Note how only the vertical stripes marked have odd numbers.
    JPS, Dec 30, 2004
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  2. So what?
    Randall Ainsworth, Dec 30, 2004
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  3. JPS

    JPS Guest

    In message <301220040605305803%>,
    So, you aren't very bright if you replied to an on-topic thread that
    doesn't interest you.
    JPS, Dec 31, 2004
  4. JPS

    G.T. Guest

    Well, I'm interested but as someone who is ignorant of what I'm looking at I
    have no idea what the significance of the odd numbers is even after reading
    your post 3 times.

    G.T., Dec 31, 2004
  5. Who gives a shit about the sequence of 1's and 0's? It's the end result
    that's important...it's about photography.
    Randall Ainsworth, Dec 31, 2004
  6. JPS

    dylan Guest

    This group's about Photography not digits ? ;oO
    dylan, Dec 31, 2004
  7. Well, actually, it's about SLR systems. I would have thought that a
    better understanding of the internals of something might have enabled you
    to make the best use of it? I think John is trying to explain something,
    without shouting it too loudly.

    Happy New Year,
    David J Taylor, Dec 31, 2004
  8. JPS

    JPS Guest

    In message <>,
    Note that I said, "that doesn't interest you"; not, "that isn't clear to

    The odd numbers are a peculiarity; I don't understand them myself. They
    occur in the raw data (which reads like english text in the image) not
    at all at the beginning of the image (where all levels are even
    numbers), then further into the image every other pixel has an odd
    level, and there are sections that are all odd as well. The DNG
    converter is not supposed to alter data at all, with the exception of
    filling in defective pixels with interpolated data (which would result
    in individual pixels breaking out of the pattern).

    One speculation that I have is that Canon is doing this to make the data
    look OK in a histogram (an equal number of odd and even values should be

    The fact, however, that the RAW data is all even or odd within patterns
    suggests that the data is not really 12-bit at its source, but rather,
    11-bit. What does this mean for the user? It means that you get the
    same quality data by setting the camera to ISO 800 instead of 1600, if
    you are shooting RAW, with an EC of -1. It also means that you get an
    extra stop of highlights this way, as the camera would clip any value
    above 2023 if the camera were set to ISO 1600.

    For those of us who shoot in low light, this is actually very beneficial
    to know. I have suspected that the camera is cheating ISO 1600 for a
    long time, and consequently, I have been setting the camera to ISO 800
    instead of ISO 1600 when shooting wildlife at dusk. That way, if there
    truly is enough light for ISO 800, I will get the better ISO 800 image,
    but if there is not enough light, it will shoot a shot that will "push"
    to ISO 1600 with the same quality and more dynamic headroom than if the
    camera were actually set to ISO 1600! I even set the EC to +1 at ISO
    800 sometimes, if there aren't a lot of bright highlights. That will
    make the aperture stop down more, when there is sufficient light
    (effectively a better ISO 400 than if the camera were actually set to
    ISO 400, because more bits represent the subject's dynamic range), but
    will also work at ISO 800, or "1600" (as good or better than the camera
    does 1600 with 0 EC) when necessary.

    Also, "ISO 3200" or "H" is actually ISO 1600, under-exposed and pushed
    by a stop, the same way.
    JPS, Jan 1, 2005
  9. JPS

    JPS Guest

    In message <311220041158443563%>,
    JPS, Jan 1, 2005
  10. JPS

    Frank ess Guest

    Frank ess, Jan 1, 2005
  11. You guys get too bogged down in the electronics/computer end of things.
    Randall Ainsworth, Jan 1, 2005
  12. JPS

    JPS Guest

    In message <>,
    JPS, Jan 1, 2005
  13. JPS

    JPS Guest

    In message <311220041738269965%>,
    It only sounds "bogged down" to you because you're simple. This is
    natural, ABC, 123 stuff to me. I'm smart enough to know that the more
    you know how things really work, the simpler it is for you to deal with
    them. Less magic, and less black boxes with no controls.

    Your less-bogged-down approach will result in images with more noise,
    and less shadow detail.
    JPS, Jan 1, 2005
  14. I doubt it.
    Randall Ainsworth, Jan 1, 2005
  15. JPS

    Alan Browne Guest

    Randall Ainsworth wrote:

    Spoken like a poor carpenter who doesn't understand tools.
    Alan Browne, Jan 1, 2005
  16. JPS

    Dustbunny Guest

    If someone told you your 8MP camera really only had 6MP, you'd be
    upset, right? Or suppose your 48-bit scanner was really only using
    16-bits. Well think of not using all the bits in those terms, maybe
    then you'll appreciate what is being described here. Or look up the
    Dustbunny, Jan 2, 2005
  17. JPS

    Colin D Guest

    Well, I'm quite familiar with bits, bytes, hex and all that, having been
    in programming for about 20 years, but I am at a loss to understand what
    you are driving at here, John. 12 bits converts to decimal 4095, or
    4096 separate steps, but the data in your graphic, since it is for
    blackframe, is averaging around 8 or 9 bits (decimal 240 - 268 approx).
    The odd numbers imply that bit 0 is a 1, that's all, but I can't see
    from this that the highest binary value is represented by 11 bits, or
    2048 decimal.

    Could you elucidate further, please?

    Colin D, Jan 2, 2005
  18. JPS

    JPS Guest

    In message <[email protected]>,
    If the winning lottery numbers were all odd one year, odd every other
    week and even on the others the next year, and all even the next year,
    what would you think? Do all numbers have an equal chance at any given
    JPS, Jan 2, 2005
  19. Please look up how little enery it needs to cool down air compared
    to water, beer and even the plastic and metal of the fridge itself.
    Buying a smaller fridge in the first place will handsomely remove
    all that empty space. This also reduces the surface of the
    refrigerator unit, thus reducing the amount of heat that leaks
    through from the outside, thus lowering your electric bill

    Your beer will not be cooler in any way, if you cool it long
    enough and don't have the door open a lot of the time.

    F'up set since OT.
    Wolfgang Weisselberg, Jan 2, 2005
  20. Oh yes, it is! Unless the 10D has a Foveon chip, which it hasn't,
    3/4 of the data has to be interpolated. Think bayer patterns
    .... and then remember that (customarily) in each row there are
    green pixels, but red and blue pixels are usually on seperate rows.
    This is but one of many possible causes. Programs have been known
    to have bugs, the bayer pattern interpolation may cause this,
    a non-perfect sensor (some cameras are even differently sensitive
    for UV light on their green pixels in alternating rows!) and many
    other causes may exist.
    Have you actually tested that, or is that just a guess? For all
    we know, the camera could also compress the highlights, e.g.:

    0-1800 => 0-3600 (i.e. *= 2)
    1801-4096 => 1801-2023 (compress) => 3602-4096 (*= 2)
    How do you think the camera handles ISO 800, 400, 200, if not by
    'cheating', if not by collecting many bits' depth at ISO 100 and
    --- in the easiest case --- simply bit-shifting them?
    Assuming the image is _better_ in a photographic sense.
    Something you can _see_ in the finalized picture.
    Unless you overexposure your image (so you actually reach that
    "headroom"), said headroom is purely theoretical and does you not
    a bit of good. You could as well shoot at 1600 then. And if you
    use anything but RAW (and thus a much more laborious workflow)
    you loose dynamic range, since JPEG compresses said range ...
    So you basically 'expose to the right'?
    And there may be special routines helping the image look better
    being run as well.

    Wolfgang Weisselberg, Jan 2, 2005
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