Re: The Joy of Pixel Density

Discussion in 'Digital Photography' started by ejmartin, Jul 20, 2008.

  1. ejmartin

    ejmartin Guest

    On Jul 20, 11:30 am, Bob Newman <> wrote:

    >
    > I think currently realised is the issue at the moment, both for sensor
    > technology and signal processing chain. In the best of all possible
    > worlds many things might be possible on both fronts. EF certainly
    > seems to have something up his sleeve, and from his slide show, it
    > seems to include really tiny pixels and really big DR. In the limit,
    > when you get to a true digital sensor, when each pixel has a FWC of
    > 1e, read noise ceases to be an issue. Near that limit, if each pixel
    > has a FWC of 2e, it's not much of an issue. This is another thing that
    > makes me think that you and Roger are not right, fundamentally, on
    > this. Somewhere between here and there, there would need to be a
    > turning point when the read noise issue stopped getting worse and
    > started getting better. In fact, I'm beginning to think I could mount
    > an inductive proof that you are wrong.> There may be in some hoped-for future a means of lowering the small
    > > pixel read noise to about 1 electron (input referred), which is not
    > > simultaneously available for bigger pixels; perhaps the reason will be
    > > the sort of capacitance arguments you have put forth.  At that point,
    > > small pixel DR on a per area basis will equal that of the 1D3's fully
    > > realized sensor DR, and small pixels will be competitive on SNR and
    > > DR.  But there is no such pixel like that among current examples.

    >
    > John and I would say, because no-one has bothered to develop it,
    > because it lies so far off the accepted orthodoxy of camera design. I
    > think that's the way Eric's going, though.


    I just remembered, while we are waiting for production small-pixel
    CMOS sensors from Canon, there is one further data point: that 52MP,
    APS-H sized sensor that they made a prototype of:

    http://www.imagesensors.org/Past Workshops/2007 Workshop/2007 Papers/076 Iwane et al.pdf

    3.3µ pixels, with 5.5 electrons of read noise. Still not getting
    smaller in proportion to pixel pitch (in fact, a bit worse; granted,
    it's preproduction, but if it were easy to beat down the read noise by
    making the pixels smaller, shouldn't they have been able to at least
    match the performance of pixels with 4 or more times the area?).
     
    ejmartin, Jul 20, 2008
    #1
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  2. ejmartin

    Bob Newman Guest

    On 20 Jul, 18:10, ejmartin <> wrote:
    > On Jul 20, 11:30 am, Bob Newman <> wrote:
    >
    >
    >
    >
    >
    > > I think currently realised is the issue at the moment, both for sensor
    > > technology and signal processing chain. In the best of all possible
    > > worlds many things might be possible on both fronts. EF certainly
    > > seems to have something up his sleeve, and from his slide show, it
    > > seems to include really tiny pixels and really big DR. In the limit,
    > > when you get to a true digital sensor, when each pixel has a FWC of
    > > 1e, read noise ceases to be an issue. Near that limit, if each pixel
    > > has a FWC of 2e, it's not much of an issue. This is another thing that
    > > makes me think that you and Roger are not right, fundamentally, on
    > > this. Somewhere between here and there, there would need to be a
    > > turning point when the read noise issue stopped getting worse and
    > > started getting better. In fact, I'm beginning to think I could mount
    > > an inductive proof that you are wrong.> There may be in some hoped-for future a means of lowering the small
    > > > pixel read noise to about 1 electron (input referred), which is not
    > > > simultaneously available for bigger pixels; perhaps the reason will be
    > > > the sort of capacitance arguments you have put forth. At that point,
    > > > small pixel DR on a per area basis will equal that of the 1D3's fully
    > > > realized sensor DR, and small pixels will be competitive on SNR and
    > > > DR. But there is no such pixel like that among current examples.

    >
    > > John and I would say, because no-one has bothered to develop it,
    > > because it lies so far off the accepted orthodoxy of camera design. I
    > > think that's the way Eric's going, though.

    >
    > I just remembered, while we are waiting for production small-pixel
    > CMOS sensors from Canon, there is one further data point: that 52MP,
    > APS-H sized sensor that they made a prototype of:
    >
    > http://www.imagesensors.org/Past Workshops/2007 Workshop/2007 P...
    >
    > 3.3µ pixels, with 5.5 electrons of read noise.

    With a column gain of 3, look at figure 5. Who knows how that compares
    with the figures obtained using the various amateur testing methods.
    > Still not getting
    > smaller in proportion to pixel pitch (in fact, a bit worse; granted,
    > it's preproduction, but if it were easy to beat down the read noise by
    > making the pixels smaller, shouldn't they have been able to at least
    > match the performance of pixels with 4 or more times the area?).

    Who knows also what the design goals were? There are reasons to keep
    the cell capacitance high, which will increase electron referred read
    noise but will also increase FWC and therefore DR. Read noise is a
    parameter the designer can trade off against other things, unless you
    know what those tradeoffs were, you can't draw any hard conclusions.
     
    Bob Newman, Jul 20, 2008
    #2
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  3. ejmartin

    ejmartin Guest

    On Jul 20, 3:37 pm, Bob Newman <> wrote:
    > On 20 Jul, 18:10, ejmartin <> wrote:
    >
    > > On Jul 20, 11:30 am, Bob Newman <> wrote:

    >
    > > > I think currently realised is the issue at the moment, both for sensor
    > > > technology and signal processing chain. In the best of all possible
    > > > worlds many things might be possible on both fronts. EF certainly
    > > > seems to have something up his sleeve, and from his slide show, it
    > > > seems to include really tiny pixels and really big DR. In the limit,
    > > > when you get to a true digital sensor, when each pixel has a FWC of
    > > > 1e, read noise ceases to be an issue. Near that limit, if each pixel
    > > > has a FWC of 2e, it's not much of an issue. This is another thing that
    > > > makes me think that you and Roger are not right, fundamentally, on
    > > > this. Somewhere between here and there, there would need to be a
    > > > turning point when the read noise issue stopped getting worse and
    > > > started getting better. In fact, I'm beginning to think I could mount
    > > > an inductive proof that you are wrong.> There may be in some hoped-for future a means of lowering the small
    > > > > pixel read noise to about 1 electron (input referred), which is not
    > > > > simultaneously available for bigger pixels; perhaps the reason will be
    > > > > the sort of capacitance arguments you have put forth.  At that point,
    > > > > small pixel DR on a per area basis will equal that of the 1D3's fully
    > > > > realized sensor DR, and small pixels will be competitive on SNR and
    > > > > DR.  But there is no such pixel like that among current examples.

    >
    > > > John and I would say, because no-one has bothered to develop it,
    > > > because it lies so far off the accepted orthodoxy of camera design. I
    > > > think that's the way Eric's going, though.

    >
    > > I just remembered, while we are waiting for production small-pixel
    > > CMOS sensors from Canon, there is one further data point: that 52MP,
    > > APS-H sized sensor that they made a prototype of:

    >
    > >http://www.imagesensors.org/Past Workshops/2007 Workshop/2007 P...

    >
    > > 3.3µ pixels, with 5.5 electrons of read noise.

    >
    > With a column gain of 3, look at figure 5. Who knows how that compares
    > with the figures obtained using the various amateur testing methods.> Still not getting
    > > smaller in proportion to pixel pitch (in fact, a bit worse; granted,
    > > it's preproduction, but if it were easy to beat down the read noise by
    > > making the pixels smaller, shouldn't they have been able to at least
    > > match the performance of pixels with 4 or more times the area?).

    >
    > Who knows also what the design goals were? There are reasons to keep
    > the cell capacitance high, which will increase electron referred read
    > noise but will also increase FWC and therefore DR. Read noise is a
    > parameter the designer can trade off against other things, unless you
    > know what those tradeoffs were, you can't draw any hard conclusions.


    One thing we can compare is DR per area; that seems to me pretty
    unambiguous (or is that mistaken?). Read noise per area scales as
    read noise per pixel divided by the sqrt of the number of pixels per
    area; FWC per area is the FWC per pixel divided by the number of
    pixels per area; thus the DR per area is some fixed number times FWC
    per pixel/(read noise per pixel * pixel spacing):

    1D3: 71000 electrons FWC/(4.0 electrons read noise * 7.2µ pixel
    spacing) ~ 2470
    40D: 40000 electrons FWC/(4.3 electrons read noise * 5.7µ pixel
    spacing) ~ 1630
    52MP prototype: 24000 electrons FWC/(5.5 electrons read noise * 3.2µ
    pixel spacing) ~ 1370

    The trend to me seems rather clear.
     
    ejmartin, Jul 20, 2008
    #3
  4. ejmartin

    Bob Newman Guest

    On 20 Jul, 23:15, ejmartin <> wrote:
    > On Jul 20, 3:37 pm, Bob Newman <> wrote:
    >
    >
    >
    >
    >
    > > On 20 Jul, 18:10, ejmartin <> wrote:

    >
    > > > On Jul 20, 11:30 am, Bob Newman <> wrote:

    >
    > > > > I think currently realised is the issue at the moment, both for sensor
    > > > > technology and signal processing chain. In the best of all possible
    > > > > worlds many things might be possible on both fronts. EF certainly
    > > > > seems to have something up his sleeve, and from his slide show, it
    > > > > seems to include really tiny pixels and really big DR. In the limit,
    > > > > when you get to a true digital sensor, when each pixel has a FWC of
    > > > > 1e, read noise ceases to be an issue. Near that limit, if each pixel
    > > > > has a FWC of 2e, it's not much of an issue. This is another thing that
    > > > > makes me think that you and Roger are not right, fundamentally, on
    > > > > this. Somewhere between here and there, there would need to be a
    > > > > turning point when the read noise issue stopped getting worse and
    > > > > started getting better. In fact, I'm beginning to think I could mount
    > > > > an inductive proof that you are wrong.> There may be in some hoped-for future a means of lowering the small
    > > > > > pixel read noise to about 1 electron (input referred), which is not
    > > > > > simultaneously available for bigger pixels; perhaps the reason will be
    > > > > > the sort of capacitance arguments you have put forth.  At that point,
    > > > > > small pixel DR on a per area basis will equal that of the 1D3's fully
    > > > > > realized sensor DR, and small pixels will be competitive on SNR and
    > > > > > DR.  But there is no such pixel like that among current examples.

    >
    > > > > John and I would say, because no-one has bothered to develop it,
    > > > > because it lies so far off the accepted orthodoxy of camera design. I
    > > > > think that's the way Eric's going, though.

    >
    > > > I just remembered, while we are waiting for production small-pixel
    > > > CMOS sensors from Canon, there is one further data point: that 52MP,
    > > > APS-H sized sensor that they made a prototype of:

    >
    > > >http://www.imagesensors.org/Past Workshops/2007 Workshop/2007 P....

    >
    > > > 3.3µ pixels, with 5.5 electrons of read noise.

    >
    > > With a column gain of 3, look at figure 5. Who knows how that compares
    > > with the figures obtained using the various amateur testing methods.> Still not getting
    > > > smaller in proportion to pixel pitch (in fact, a bit worse; granted,
    > > > it's preproduction, but if it were easy to beat down the read noise by
    > > > making the pixels smaller, shouldn't they have been able to at least
    > > > match the performance of pixels with 4 or more times the area?).

    >
    > > Who knows also what the design goals were? There are reasons to keep
    > > the cell capacitance high, which will increase electron referred read
    > > noise but will also increase FWC and therefore DR. Read noise is a
    > > parameter the designer can trade off against other things, unless you
    > > know what those tradeoffs were, you can't draw any hard conclusions.

    >
    > One thing we can compare is DR per area; that seems to me pretty
    > unambiguous (or is that mistaken?).  Read noise per area scales as
    > read noise per pixel divided by the sqrt of the number of pixels per
    > area; FWC per area is the FWC per pixel divided by the number of
    > pixels per area; thus the DR per area is some fixed number times FWC
    > per pixel/(read noise per pixel * pixel spacing):

    No, I don't think it's ambiguous, and I think it is a good figure of
    merit.
    > 1D3: 71000 electrons FWC/(4.0 electrons read noise * 7.2µ pixel
    > spacing) ~ 2470
    > 40D: 40000 electrons FWC/(4.3 electrons read noise * 5.7µ pixel
    > spacing) ~ 1630
    > 52MP prototype: 24000 electrons FWC/(5.5 electrons read noise * 3.2µ
    > pixel spacing) ~ 1370
    >
    > The trend to me seems rather clear.

    Yes, except that that sort of data analysis wouldn't pass muster in
    any serious context. We have three samples which appear to show a
    trend. If we accept that there is a trend (and three samples is a
    rather small number on which to base it!) we still don't know why
    there's a trend. As I suggested to Roger Clark, these are designed
    artifacts, we do not know what the designer is aiming for. I'd hazard
    a guess that designers of high megapixel DSLR's are aiming at maximum
    IQ at low ISO's, in which case they'll put the capacitance of the
    sensel as high as feasible within the space constraints of the pixel,
    since increased FWC gives increased pixel level DR. This will
    adversely affect read noise/ area.
    > - Hide quoted text -
    >
    > - Show quoted text -
     
    Bob Newman, Jul 21, 2008
    #4
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