Canon high ISO rumour - article

Discussion in 'Canon' started by RichA, Jan 13, 2007.

  1. RichA

    RichA Guest

    RichA, Jan 13, 2007
    #1
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  2. While I generally have great respect for Westfall, the comment
    seems pretty out of place. In the beginning of the article,
    they state quantum efficiencies (QE) range from 25 to 70% (correct).
    So how does one get a factor of 16 (hint: you can't go
    greater than 100% QE). If they mean small
    pixel size P&S cameras of today could someday perform
    like todays DSLRs by a modest increase in QE in combination
    with larger sensor and pixel size, then I'll agree.
    But no one has found a way to reduce noise beyond
    photon counting noise, which is a physical limit.
    Note in the article right after the Westfall statement,
    the Foveon guy didn't believe it either.

    More info on pixel effects size as discussed in the story:
    http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary

    Roger
     
    Roger N. Clark (change username to rnclark), Jan 13, 2007
    #2
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  3. RichA

    Rudy Benner Guest

    You might see a demonstration on Miami CSI.
     
    Rudy Benner, Jan 13, 2007
    #3
  4. You don't need more width you need more volume of active silicon.
    You can do this by making the cells deeper and still have the same physical
    size.
    This technique is used in DRAM to make the cells hold more electrons.

    Any such technique could be applied to larger sensors too, so newer DSLRs
    will still have an advantage over compacts even though current DSLRs may
    produce worse picture quality than newer compacts.

    There has to be some driving force to get people to upgrade now that digital
    exceeds the resolution of film (and the lenses). ;-)
     
    [email protected], Jan 13, 2007
    #4
  5. RichA

    Jan Böhme Guest

    [email protected] skrev:
    That would increase the dynamic range, which in and by itself would be
    a very good thing, actually better than increasing sensitivity further
    IMO. (Phtotogs are ungrateful. They have already forgotten that DSLR:s
    already have given them much higher ISO sensitivity for colour
    photography than they could get with film. They just want to get even
    more.)

    But how coulld it increase sensitivity? If essentially all incident
    photons already are trapped until well saturation becomes limiting, how
    could improving well capacity lead to higher sensitivity?

    Jan Böhme
     
    Jan Böhme, Jan 13, 2007
    #5
  6. Most output media can handle at most about 6 stops. Increasing dynamic
    range without reducing noise levels simply means lower ISO values,
    which require longer exposures, which are (except for landscapes) a
    problem.
     
    Philip Homburg, Jan 13, 2007
    #6
  7. RichA

    HarryO50 Guest

    Most Canons that I see don't do well much above 400 iso. I try to keep
    my XT at 200 most of the time. I get no grain, no noise, that way.
    The new XTi is probably the same way. I'd give my eye teeth to get my
    hands on one of those bodies. I might just do it when funds are
    available. I'm selling some old equiment on ebay now, in hopes of
    raising enough to get the XTi body.

    Harry
     
    HarryO50, Jan 13, 2007
    #7
  8. RichA

    HEMI-Powered Guest

    Today, HarryO50 made these interesting comments ...
    Harry, I have a year-old XT which works well, although my
    experience matches yours on noise above ISO 200. Besides the
    extra 2 MP, what specific features/improvements do you see in the
    XTi?
     
    HEMI-Powered, Jan 13, 2007
    #8
  9. Jan,
    Your are correct, increasing the well size only increases
    the photons collected and thus the dynamic range.
    It does nothing to change sensitivity.

    Pixel size also determines true sensitivity. Larger
    pixels collect more photons and photons/pixel/time
    is sensitivity. Camera manufacturers define ISO to be a fraction
    of full well capacity, thus a sliding scale. We see the
    result in noise: small cameras have more noise; it is
    a fundamental physical limit (photon counting statistics).

    More info on this subject:

    Digital Cameras: Does Pixel Size Matter?
    Factors in Choosing a Digital Camera
    http://www.clarkvision.com/imagedetail/does.pixel.size.matter

    Digital Cameras: Does Pixel Size Matter?
    Part 2: Example Images using Different Pixel Sizes
    http://www.clarkvision.com/imagedetail/does.pixel.size.matter2

    The f/ratio Myth and Digital Cameras
    http://www.clarkvision.com/photoinfo/f-ratio_myth

    Roger
     
    Roger N. Clark (change username to rnclark), Jan 13, 2007
    #9
  10. If you say this, then no camera does well. Canon DSLRs are
    regarded by astrophotographers as the top performing digital
    cameras (only cooled CCDs are better). The noise statistics
    I presented on the page:

    http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary

    shows that. In particular look at Figure 3 (read noise),
    Figure 6 (ISO at unity gain), and Figure 7 (low signal sensitivity).

    If you don't like the noise from a DSLR, you'll hate the
    noise from a small pixel P&S camera ;-). For example,
    compare the iso 1600 images from a DSLR to ISO 100
    images from a P&S:
    http://www.clarkvision.com/imagedetail/does.pixel.size.matter2

    Roger
     
    Roger N. Clark (change username to rnclark), Jan 13, 2007
    #10
  11. I don't think ISO is determined by just the full well capacity.
    It is combination of the full well capacity and the sensitivity.

    Higher sensitivity results in a higher ISO, but a higher full well capacity
    results in a lower ISO.
     
    Philip Homburg, Jan 13, 2007
    #11
  12. RichA

    nick c Guest

    Oh!!

    Reference to two test cases:

    http://www.pbase.com/nchen711/image/72995412

    http://www.pbase.com/nchen711/image/72653897
     
    nick c, Jan 13, 2007
    #12
  13. Sorry.
    I answered the wrong question (again!, it must be age).

    It should increase the dynamic range.

    I suppose if you want to do something really radical you could have an
    individual photon counter per pixel.
    Then you would have sensitivity and dynamic range.
    It would bring digital cameras into the digital age too.
     
    [email protected], Jan 13, 2007
    #13
  14. RichA

    G.T. Guest

    Good question. I upgraded from a Rebel to a Rebel XT for several
    reasons but my next upgrade will be to at least the 30D level, maybe the
    5D level. I don't see much reason to move from the XT to the XTi.

    Greg
     
    G.T., Jan 13, 2007
    #14
  15. Unfortunately, DRAMs don't record photons not coming in at a
    vertical angle very well ...
    Picture quality is not just (absense of) noise. Show me one
    8MPix camera where the optics can really deliver the resolution
    the sensor records.

    -Wolfgang
     
    Wolfgang Weisselberg, Jan 13, 2007
    #15
  16. I said that full well capacity does not change sensitivity.
    I said true sensitivity is photons/pixel/time. Regardless
    of well capacity and relative response of the ISO
    definition, true sensitivity is a function of pixel
    size and quantum efficiency, with larger formats giving
    better sensitivity, assuming the same megapixel count.
    The larger pixels simply collect more photons much like
    a larger bucket collects more rain drops than a smaller
    bucket. The larger bucket may not fill up any faster,
    but more you do get more rains drops. Same with pixels
    and photons. But noise in digital camera images is
    dominated by photon counting statistics, so larger pixels
    collectong more photons give better images.

    Roger
     
    Roger N. Clark (change username to rnclark), Jan 14, 2007
    #16
  17. Of course a change in the full well capacity changes the ISO
    sensitivity. If you double the full well capacity then you need twice
    the photon count to get it full. So you have half the ISO.
    True _quality_ is dictated by time*photons/CFA-pixel.
    How do you define "true sensitivity"? When you have two sensors with the
    same qe, same CFA-mask and the same full well capacity but one has 2x
    the CFA-pixel active area than the other, then in your opinion does the
    2x provide a higher "true sensitivity"? When all other aspects are held
    the same, the sensor with the 2x CFA-pixel area of course has 2x the ISO
    but it means that only half of the dynamic range that the 2x CFA-pixel
    could provide is being used. This does not mean "true sensitivity" but
    false sensitivity.
    Better _quality_.
    That is correct, you simply need a larger bucket to collect them all.
    Yes, better _quality_ images. Then, when that quality is high enough, it
    is possible to provide false sensitivity by reducing that high quality,
    by using only a small portion of the full dynamic range that the
    camera is capable to provide. Just like it is being done in all the
    cameras even if the true quality of these cameras do not warrant such
    reduction.

    My understanding is that the true sensitivity of sensor is a function of
    qe, fill factor and the transmittance of the CFA-mask only.

    Timo Autiokari
     
    Timo Autiokari, Jan 14, 2007
    #17
  18. RichA

    Prometheus Guest

    The number of photons entering a well of unit area in unit time is
    independent of the depth of the well. Imaging that 1000 photons pass
    through a 3 micron diameter opening in to a well in 1ms; how does making
    the well deeper increase the number of photons? The only ways of making
    the well more sensitive are to either make the area larger or improve
    the efficiency. With current efficiencies of ~30% there is limited
    potential in that route. Making the well deeper will improve the dynamic
    range thus allowing you to capture more shadow detail without blowing
    highlights, it can NOT capture more photons per unit time.
     
    Prometheus, Jan 14, 2007
    #18
  19. That is correct.
    No, making the well deeper (increasing the full well capacity) and doing
    nothing else affects to nothing.

    But doing so provides you the possibility to collect a longer time. So
    when you double the full well capacity _and_ you also double the
    collecting time then, and only then, you will have improved dynamic range.

    Doubling the collecting time in the above example (while keeping the
    concept of camera unchanged) can only be achieved by introducing an
    other ISO sensitivity setting that is half of that ISO setting that was
    effective before the doubling of the full well capacity.

    Timo Autiokari
     
    Timo Autiokari, Jan 14, 2007
    #19
  20. RichA

    Jan Böhme Guest

    Philip Homburg skrev:
    True. But this isn't all that relevant for how many stops of
    sensitivity it would be advantageous for the image recording to have.
    In practically all the cases where you really need higher dynamic
    range, it _isn't_ a problem, though. These situations typically involve
    images which in part are lit with bright sunlight. And higher dynamic
    range without reducing noise levels doesn't _simply_ mean lower ISO
    values. It means lower ISO values with better shadow resolution. So you
    expose for your highlight, which should take quite a low ISO at normal
    shutter speed and aperture if you really need the extra dynamic range,
    and get your desired resolution out of the shadows.

    If we talke today's DR as natural, the best way of describing a higher
    dynamic range in ISO terms is that you can use a lower ISO for the
    highlights and a higher one for the shades, in the same exposure.

    Jan Böhme
     
    Jan Böhme, Jan 14, 2007
    #20
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