Canon to address "blown highlights" in 2007?

Discussion in 'Canon' started by RichA, Mar 22, 2006.

  1. RichA

    RichA Guest

    According to Pop Photography, Canon is going to bring out something in
    2007 to fix the
    inability of sensors to deal with wide dynamic ranges. They (Pop
    Photography) said they'd say what it is next month. I'm wondering if
    they've figured out a way to regulate the sensitivity of individual
    pixels in an array by varying something (signal amplification?).
     
    RichA, Mar 22, 2006
    #1
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  2. RichA

    D-Mac Guest

    You mean like the Sony sensor in Fuji DSLRs?
     
    D-Mac, Mar 22, 2006
    #2
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  3. No, its call more pixels just like MF backs do today.


    --

    "I have been a witness, and these pictures are
    my testimony. The events I have recorded should
    not be forgotten and must not be repeated."

    -James Nachtwey-
    http://www.jamesnachtwey.com/
     
    John A. Stovall, Mar 22, 2006
    #3
  4. RichA

    ian lincoln Guest

    fuji dslrs use fuji sensors.
     
    ian lincoln, Mar 22, 2006
    #4
  5. RichA

    D-Mac Guest

    Yes, like the one they get from Sony?
     
    D-Mac, Mar 22, 2006
    #5
  6. RichA

    ian lincoln Guest

    only fuji produce the paired pixel sensor for extra dynamic range. It is
    patented. I suppose they may pay sony to produce them to spec but i doubt
    it. However KM and Nikon do use Sony sensors.
     
    ian lincoln, Mar 23, 2006
    #6
  7. RichA

    D-Mac Guest

    I thought ony Wedding Photographers were pedantic.
    I'll rephrase then: Like to one they get Sony to make?
    Satisfied now?
     
    D-Mac, Mar 23, 2006
    #7
  8. Canon DSLRs already have very large dynamic ranges, limited by
    12-bit A-to_D converters. The 1D mark II, for example, has
    measured dynamic range (max signal/read noise) > 3000:1,
    or 11.6 stops. See:
    http://www.clarkvision.com/imagedetail/evaluation-1d2

    This is already greater than film (even print film):
    http://www.clarkvision.com/imagedetail/dynamicrange2

    I've not seen any data on the Fuji sensors. Can they
    actually do better than 11.6 stops?

    Roger
     
    Roger N. Clark (change username to rnclark), Mar 23, 2006
    #8
  9. RichA

    Rich Guest

    They had an example of film versus digital DSLRs. The negative film
    was exposed 3 stops over and was able to produce a good image, it
    simply required more light through a dense negative.
    The digital image was blown completely. Maybe it's time for
    them to move to 16 bit A to Ds?
    -Rich
     
    Rich, Mar 23, 2006
    #9
  10. RichA

    ian lincoln Guest

    nope
     
    ian lincoln, Mar 23, 2006
    #10
  11. But its a "hard" clip with the digital sensor and a "soft" clip on film.
    Its a bit like the old comparison of transistor and valve audio
    amplifiers - transistors gave better linearity and distortion than
    valves when operating well within their range, but valves sounded better
    because they clipped softly compared to the awful distortion produced by
    hard clipping transistors when driven by the occasional transient beyond
    their nominal range.

    A non-linear top end response to a digital sensor would eliminate the
    problem of blown highlights due to unexpected specular reflections. Say,
    linear response to 90% of the existing capacity and logarithmic response
    in the top 10%. It wouldn't take any additional photodiodes, as Fuji
    use, just the response of the CMOS buffer circuit, and flexibility of
    the pixel design is one of the key benefits of CMOS over CCDs.

    In fact, can't this be done with just two additional diodes, one of
    which is a zener, in a feedback loop around the amplifier in the pixel?
     
    Kennedy McEwen, Mar 23, 2006
    #11
  12. RichA

    eawckyegcy Guest

    Maybe it's time for you to grow a brain? If the pixel well is
    saturated, even a 1000 bit ADC isn't going to help.
     
    eawckyegcy, Mar 23, 2006
    #12
  13. RichA

    JPS Guest

    In message <>,
    I would think that the big issues that get in the way are ones of
    calibrating the pixels to all have the same response in the RAW data.
    It's hard enough getting a few thousand rows and columns of single
    linear pixel readouts to have the same gain and blackpoint.
    --
     
    JPS, Mar 23, 2006
    #13
  14. RichA

    JPS Guest

    In message <>,
    True, but if the RAW data had more dynamic range, you could afford to
    expose with more headroom as a default.
    --
     
    JPS, Mar 23, 2006
    #14
  15. RichA

    Colin D Guest

    As I understand the problem, highlight clipping is due to one or other
    of two effects. One, full wells. Given the dynamic range of good
    sensors, only an exposure long or large enough to cause well saturation
    can cause clipping by this means; and it should only be possible if
    shooting at the camera's lowest ISO. Shooting at higher ISO numbers
    results in fewer photons being captured because of the faster exposure,
    so full-well clipping at higher ISO's is a remote possibility, only
    perhaps with extremely bright specular reflections or gross
    overexposure.

    Two, the amplifier gain employed by the processor can cause clipping in
    jpeg images with only slight overexposure, as all highlights that exceed
    255,255,255 in any amplified channel will be clipped, even if the sensel
    well was not full.

    RAW data processed in good converter software allows the effective gain
    to be adjusted to place the histogram where the operator wants it, so
    fixed-gain clipping problems are avoided.

    I have wondered if jpeg processing in-camera would benefit from some
    sort of automatic gain control, based on how much lift is needed to
    place the highlights just short of clipping, rather than fixed gain
    controlled by ISO. Maybe the manufacturers do this already since it
    seems obvious, but there could be drawbacks like a processing penalty
    and space for the additional firmware, and a fixed safety margin might
    be preferable - in which case the safety margin should be controllable
    by the photog. Come to think of it, it is already controllable by
    exposure compensation. However, a dynamic control based on the
    individual exposure would be better.

    Colin D.
     
    Colin D, Mar 24, 2006
    #15
  16. If you examine the dynamicrange2 web site above, you would see for
    the 1D mark II that the hard clip of the digital sensor is only 2/3 stop
    below the print film, and 1/3 stop above slide film. This is for
    getting any information off the film with a 16-bit scanner.

    But then the digital goes way below the print or slide film in the
    shadows.
    The problem is the full well. The photons convert to electrons in
    a linear process, so even if you want to encode the output
    non-linearly, the sensor is still inherently linear and has
    a full well.

    All canon, or any other manufacturer would have to do is add more
    bits, and include some in headroom. For example, the 1D Mark II
    sensor full well is 80,000 electrons, but the ISO 100 maximum
    signal is about 53,000 electrons. With some extra bits,
    you could have about 2/3 of a stop more headroom.

    Many canon cameras already have a bit shift for jpeg data,
    which auto shifts the data if the jpeg will saturate.
    It is a custom function to turn on. I use it all the time.

    Roger
     
    Roger N. Clark (change username to rnclark), Mar 24, 2006
    #16
  17. RichA

    Rich Guest

    With regard to the shadow detail in digital. What does it matter if
    its there if it consists of near black and white "colour" and next to
    no tonal gradations? If you bring up the level enough to see it, it
    looks so odd and so ugly you might rather have it as black or near
    black.
    -Rich
     
    Rich, Mar 24, 2006
    #17
  18. RichA

    Rich Guest

    Astronomical CCD cameras constantly saturate pixels (owing to bright
    point sources being images) and yet use 16 bit D/As.
    -Rich

    http://www.sbig.com/sbwhtmls/online.htm

    Astrophotographers take note: A 35mm format CCD with 11 million
    pixels. Another revolution in astrophotography is about to take
    place. If you have been waiting for a wide field CCD with the same
    coverage as 35mm film, here it is. Only this one is cooled, linear,
    self-guiding, 16 bits and optimized for high sensitivity and low noise
    performance in low light astronomical applications.
     
    Rich, Mar 24, 2006
    #18
  19. RichA

    Paul Furman Guest

    How exactly do the photodiodes work? Do the 'wells' really have depth?
    Thicker silicon chips?
     
    Paul Furman, Mar 24, 2006
    #19
  20. The "well" is a potential well where electrons get trapped.
    Yes, it does have physical size, much as a capacitor has
    physical size. Larger pixels have larger potential wells
    allowing more electrons to be collected.

    Roger
     
    Roger N. Clark (change username to rnclark), Mar 24, 2006
    #20
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