From: David J Taylor on
Lionel wrote:
> On Sat, 17 Mar 2007 14:43:32 +1100, Lionel <usenet(a)imagenoir.com>
> wrote:
>
>> On Sat, 17 Mar 2007 12:07:08 +0900, "David J. Littleboy"
>>> Also, my understanding (possibly wrong) is that the CCD/CMOS
>>> sensors are fabricated in technology that's multiple generations
>>> behind the DRAM/microprocessor/ASIC curve, so there's actually
>>> quite a bit of room for improvement in the circuits.
>
> Now that I think about this further, I've realised that you're
> probably thinking of minimum feature-size, which is vitally important
> for DRAM & other digital circuits, but isn't terribly useful for image
> sensors. Image sensors can be made with older fabrication technologies
> because photodiodes as small as modern DRAM cells would (I think!) be
> too small to usefully detect photons.

But the smaller feature size might reduce the space occupied by the
support structure and thereby improve the fill-factor.

David


From: John Sheehy on
Lionel <usenet(a)imagenoir.com> wrote in
news:4vvmv2tfk3eb63cem762dmh1rfbjf592g4(a)4ax.com:

> On Sat, 17 Mar 2007 05:33:58 GMT, John Sheehy <JPS(a)no.komm> wrote:

>>Read noise is more of a problem when you have less and larger pixels.
>>Really.

> No, it's categorically not. The bigger the signal, the easier it is to
> amplify & convert accurately.

At the pixel level. I don't worship pixels. I use them to record
images. having more of them, with slightly less accuracy each, has more
useful resolution information about the subject, and when binned, has
less read noise. This is what is happening now in the real world,
despite your boogey-man stories. Did you read the figures for the FZ50
pixels binned to DSLR size? 8.1 electrons of read noise, out of a max of
43,200 photons, at ISO 100. That is what is real, right now. Forget
your boogey-man read noise horror stories.

> As the signal level decreases, it
> eventually drops below the noise floor, & can only be detected by
> statistical means, over multiple repeated samples. This is a
> fundmental fact in electronics.

The "noise floor" is determined by the electronics used, and as useage
changes, so does the electronics. Think about Canon high ISO - very low
read noise for small signals; less noise in electrons at higher ISOs,
where there are *SMALLER SIGNALS*. Your generalization falls apart in
reality.

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John P Sheehy <JPS(a)no.komm>
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From: John Sheehy on
Lionel <usenet(a)imagenoir.com> wrote in
news:85vmv2ttgd09e4c6gq47mkrojj5pbme1kq(a)4ax.com:

> On Sat, 17 Mar 2007 05:18:31 GMT, John Sheehy <JPS(a)no.komm> wrote:
>
>>Lionel <usenet(a)imagenoir.com> wrote in
>>news:1gnmv2115h3hk123mthqv4seor0cs0ri2d(a)4ax.com:
>>
>>> Having said that, assuming that microlenses work similarly to lenses
>>> at the macro level, on the one hand, they should definitely help
>>> improve the signal to noise ratio at the level of the individual
>>> photodiode, but on the other hand, will fill the smaller well sooner,
>>> decreasing the effective dynamic range of each pixel.
>>
>>Microlenses have zero effect on dynamic range.
>
> Not so.

You say "Not so", then you imply "Yes so":

> Each photodiode has a maximum well capacity that determines
> its dynamic range.

Which is exactly why microlenses have no effect on DR. No matter how
big, small, or absent your "light funnel", the S/N at any given level in
the RAW data is exactly the same; the 1:1 S/N is the same number of stops
below saturation for any microlens; and that follows for 10:1, 3:1, 1:2,
or any ratio you deem as "minimum usable".

> When it's full, any excess is lost, & will either
> leak into adjacent areas, causing errors or 'blooming', or must be
> dumped into 'drains', which require more non-light sensitive surface
> area.

This is all relative. The microlens coverage is equivalent to using
variable neutral density filters, as far as signal level is concerned.
ND filters do not affect DR.

>>> And because the
>>> output signal will still be small, you'll get more amplifier noise
>>> when you read the signal from the pixel.

>>But not relative to absolute exposure.

> That would be true if you're using theoretical perfect amplifiers.
> It's not the case with real world amplifiers.

Think Canon high ISO. Less noise in electrons, at higher gain. That's
real world. The small-pixel cameras tend to have very good read noise at
ISO 100, and poor amplifiers for high ISO; worse than pushing. Better
can be done.

>>Noise per pixel or per unit of sensor area?

> Both. At the macro level, it'll manifest as decreased dynamic range.
> (See Roger Clarke's dynamic range vs ISO graphs for a real world view
> of how this effect would appear.)

Roger has a knack for testing one thing, and drawing conclusions about
another. My tests show that low noise in big pixels is only an advantage
when magnifying the *PIXELS* at the same size; not the subject - when the
same focal length, Av, Tv, and ISO are used. Roger compares large
pixel,large sensor to small pixels, small sensor, with equivalent FOV,
and then draws conclusions about small *pixels*. That is wrong. The
conclusions should be about small *sensors*.

> (Hm. That's just given me a couple of interesting ideas as to how
> Canons noise reduction systems work. Multi-pattern spatial
> sub-sampling & integration, perhaps? Something like that might explain
> a lot about the noise characteristics of Canons high ISO images...)

That is a real-world example of how small signals are not necessarily
read out with more noise in electrons, even without binning.

Stop defending the myth, and start thinking.



--

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John P Sheehy <JPS(a)no.komm>
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From: John Sheehy on
Lionel <usenet(a)imagenoir.com> wrote in
news:r60nv2d39ob8k77b6bok3lcos9t1qhd25l(a)4ax.com:

> On Sat, 17 Mar 2007 05:40:31 GMT, John Sheehy <JPS(a)no.komm> wrote:

>>... and the more pixels covering an area, the less important the
>>accuracy of any one pixel is.

> Ah, but your larger photodiode+amp *can* still accurately detect
> individual photons that the photodiodes+amps in your sub-array of the
> same size /won't/ be able to accurately detect. That's exactly my
> point.

Huh? That doesn't make any sense.

In order for what you say to be true, the smaller pixels would have to
have a read noise at least 4x as high as that in pixels 4x as large. 4
pixels into one means 4x the signal, and 2x the noise, for an increase in
S/N of 2x.

In all these arguments against what I'm saying, I see people fabricating
high read noises for small pixels that don't happen in real life. I'm
supposed to believe the boogey-man stories of the hand-wavers who accuse
me of hand-waving, and none have actually taken the trouble to see what
happens in the real world with available products.

Take any blackframe; load into a program that bins, check the standard
deviation before and after. For an NxN bin, signal increases by a factor
of N^2, and noise increases by N, for an increase in S/N of N times.
That would require N times as much noise in the smaller pixel to equal
the larger, after binning, and more than N times to make it worse.

--

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John P Sheehy <JPS(a)no.komm>
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From: acl on
On Mar 17, 6:35 pm, John Sheehy <J...(a)no.komm> wrote:

> Roger has a knack for testing one thing, and drawing conclusions about
> another. My tests show that low noise in big pixels is only an advantage
> when magnifying the *PIXELS* at the same size; not the subject - when the
> same focal length, Av, Tv, and ISO are used. Roger compares large
> pixel,large sensor to small pixels, small sensor, with equivalent FOV,
> and then draws conclusions about small *pixels*. That is wrong. The
> conclusions should be about small *sensors*.

Even ignoring all the mess in this thread, it has always irritated me
how people measure the noise stdv and compare it between cameras as if
nothing else matters. Obviously a given noise frequency spectrum
(spatial frequency in terms of pixels) will have a different visual
effect (when printed to a given size) if present in a 6mp image or a
12mp image. Of course, some thought about this results in what is
being "discussed" here, ie binning and addition of noises and how
things may be scaled, and I reached similar conclusions to yours some
time ago (although I never measured anything, I just thought about it
a bit).

But I never bothered mentioning anything here for reasons that I think
are now obvious, to wit that everybody will start inventing reasons
that it cannot be done, they'll argue against 1 angstrom-sized pixels
as if this is what is being proposed, not bother to read what is
written because they already know the answer etc.

And anyway, in 5-10 years I'll buy a very high mp small-sensor camera
with built-in binning ability whether people here agree now or not.