logarithmic cameras (SLR or otherwise)

Discussion in 'Digital Photography' started by jonathan, Dec 15, 2003.

  1. jonathan

    jonathan Guest

    hey all,

    I was wondering if anyone had any news on the state of logarithmic
    cameras; for night shots, I've been doing tons of autobracketing,
    stitching (as in panotools and PTGUI), and contrast masking to
    overcome what is really a technology issue - that both film and
    standard CMOS cameras don't have nearly enough contrast range to
    handle the large light variation that happens in lots of different

    Anyways, when I search the web for logarithmic sensors, I don't come
    up with much except a couple of 'experimental' sensors for
    applications like machine vision; I was hoping that someone might have
    a good overview of where this technology is, and how fast it might get
    to market.

    anyone got some pointers or a good summary?


    jonathan, Dec 15, 2003
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  2. jonathan

    DJ Guest

    A logarithmic response would seem like a great idea to get more dynamic range,
    or "lattitude" in photographic parlance. There are 2 problems with this, as I
    see it:

    1. Silicon sensors are inherently linear when used in photo current mode. That
    is the mode used in camera sensors because the photo current, proportional to
    light level, is integrated over the time of the exposure. Photo diodes used in
    voltage mode (e.g. for power generation) are logarithmic, but there is probably
    no feasible way of using voltage mode in a camera sensor.

    2. One might propose a linear sensor array followed by a logarithmic amplifier.
    What this would actually amount to is increasing the amplification for low light
    levels and reducing it for high levels. However, the noise would get you.

    I practice I think it's safe to say that using 12 bit RAW mode (who knows, maybe
    14-bit or 16-bit in future cameras) extracts just about everything that can be
    extracted from the sensor at the current noise levels.

    DJ, Dec 15, 2003
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  3. jonathan

    jonathan Guest

    well, that's the source of my frustration (I've shot raw and I've used
    DSLR pro). It extracts way too little (or too much, depending on your
    point of view) and no matter what kind of spin you put on the picture
    in either DSLR pro or photoshop, the shot doesn't come out how you
    actually see the scene at night. You can approximate it with lots of
    work, but that's about it. things get blown out too easy.

    I'd imagine that this would be a *big* incentive for camera
    manufacturers - I can see their adverts: 'perfect frames every time!'
    and 'our camera takes pictures the way the eye sees!' But I don't
    know enough to say whether the difficulties you mention are
    engineering difficulties to overcome or physical impossibilities.

    I'd guess the former, but that's just me, and what do I know :)

    jonathan, Dec 15, 2003
  4. jonathan

    DJ Guest

    Yesterday's physical impossibilities have a tendency to lead to tomorrow's
    engineering achievements, so who knows? :)
    DJ, Dec 16, 2003
  5. jonathan

    JPS Guest

    In message <>,
    You could take a RAW converter that outputs linear data, and stack
    several images taken at ISO 100, and then do your own curves. Some of
    the linear converters don't scale the images to full histogram, so they
    fall in a range like 0 to 63 or 0 to 15 (out of 255), and in that case,
    you could add several of them without even having to average them. I
    don't know when I'm going to get around to it, but I was going to alter
    dcraw.c to output uninflated values that ignore blackpoint, so that I
    can get the *real* raw data out of the files. You should be able to add
    16 of them together, at least, without any averaging.
    JPS, Dec 18, 2003
  6. jonathan

    JPS Guest

    In message <>,
    Sounds to me like you're simply overexposing, and/or not doing the RAW
    conversion with the right tools.
    JPS, Dec 18, 2003
  7. jonathan

    jonathan Guest

    I'm using DSLR pro, which *does* support histogram manipulation, and
    does support curves. It also supports manipulation of exposure values.
    I've never been able to get the exact effect I want (seeing with the
    camera what my mind's eye sees at night) without a tripod, low ISO
    levels, a fast fast lens and a non-trivial amount of effort. And
    sometimes not even then. Simple manipulation of raw doesn't get me

    When you say 'take several images at ISO 100' I'm assuming you mean
    the same image - which limits me to the above. Or are you meaning
    something different? And what is dcraw.c? Is it a package or a c file?

    jonathan, Dec 30, 2003
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