From: acl on
On Mar 17, 11:22 pm, "Roger N. Clark (change username to rnclark)"
<usern...(a)qwest.net> wrote:
> John Sheehy wrote:
> > 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.
>
> John, you are confusing several things in your argument in this thread.
> 1) Small pixel size cameras are at near unity gain at low ISO.
> (for other readers, unity gain ISO is the ISO where 1 electron
> equals one bit in the A/D converter). ISO's above unity gain
> ISO is nothing more than "digital ISO." You essentially gain
> nothing at higher ISOs as you can't measure a fraction of an electron.
>
> 2) Current DSLR cameras, like the Canon 20D, Nikon D50, and all other
> DSLRs tested on my web pages and other people testing cameras
> that I reference, ARE NOT SENSOR READ NOISE LIMITED AT LOW ISO.
> You cite the high read noise of DSLRs at low ISO in electrons,
> but that is an electronics limitation, NOT sensor limitation.
>
> 2a) As electronics improve, e.g we see that in the newly announced
> canon 1D mark III with 14-bit converter, the low ISO noise
> is reduced (according to Canon). Current scientific sensors
> use 16-bit converters and achieve full well digitization with
> good digitization of true sensor read noise. We'll see that
> soon in coming DSLRs.
>
> 3) So what you are describing as lower read noise for binned small
> pixel sensors, is really because the small pixel cameras are operating
> at near unity gain ISOs, while the DSLRs are not. You are comparing
> apples and oranges. (Interesting that DSLRs are not yet living up
> to their low ISO potential! That is exactly what is shown in Figure 4 at
> http://www.clarkvision.com/imagedetail/digital.sensor.performance.sum...
> where the P&S small sensors are below the 12-bit line and the DSLRs are
> above the line indicating they are A/D electronics limited. Note the
> data indicate the 1D Mark II and 5D would still be limited with 14-bit
> converters, so the new 1D Mark III will still not quite live up to its
> potential.)
>
> 4) DSLRs do not live up to their full low signal, low ISO potential because they
> are A/D limited. Remember, all A/D conversions are accurate to +/- 1 bit.
> A DSLR with 50,000 electron full well (e.g ~ Canon 20D) and a
> 12-bit converter digitizes 1 bit = 50000/(2^12 -1) = 50000/4095 = 12.2 electrons.
> 14-bit converter digitizes 1 bit = 50000/(2^14 -1) = 50000/16383= 3.05 electrons.
> The read noise of the 20D sensor is 3.9 electrons. 14-bits is close to
> digitizing that well but 12-bits is not (remember the +/- 1 bit added noise).
>
> > Lionel <use...(a)imagenoir.com> wrote in
> >news:85vmv2ttgd09e4c6gq47mkrojj5pbme1kq(a)4ax.com:
>
> >>> 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.)
> > John Sheehy 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*.
>
> The current crop of available cameras gives choices like:
> 8 megapixel P&S small sensor, small pixel camera versus
> 8 megapixel DSLR with large pixels. I provide data and information
> for people to evaluate what they would lose in making a choice
> between such cameras. THAT IS NOT WRONG.
>
> For those new to my web sites, relevant web pages are at:http://www.clarkvision.com/imagedetail/index.html#sensor_analysis
>
> John, your assertion seems to be (correct me if I'm wrong):
> Given two sensors of the same total size, one with large pixels,
> and one with small pixels, the small pixel camera can deliver
> equal quality images when the pixels are binned to the
> size of the larger pixels. You then support this by saying
> the low ISO read noise of DSLRs is larger than at high ISOs
> and at low ISOs is larger than small pixel cameras.
> You bolster your argument using currently electronics limited
> DSLRs with fictitious small pixel sensors that have many times
> the pixels currently available in any sensor (e.g. your 223 megapixel
> sensor or something like that).
>
> So with the fact that current 12-bit DSLRs must be limited in their
> read noise at low ISOs and the fact that 16-bit scientific sensors
> available (even amateur astronomers have such chips), it is a
> matter of time before we see the DSLRs with lower effective read noise,
> e.g. as is the case with the new 1D Mark III.
> So, I think you should level the playing field and use true sensor
> read noise in your calculations. When you do, you'll find this
> is a common sampling problem and is encountered in science all the
> time. The noise in any one measurement has an error. The smaller
> the signal, the lower the signal to noise ratio of that measurement.
> Adding multiple samples improves as the square root of the number
> of samples.
>
> So in the level playing field of equal read noise in both large and
> small sensor, the small sensor binned up to the large sensor will have
> read noise higher by the square root of the number of pixels binned.

Hi. I am obviously not JPS. Basically, you and everybody else who
disagree with what he says keep repeating this as if it was never
mentioned, and imply that it negates his argument. It doesn't. For a
uniform subject, it's true that if I have two sensors of the same size
but with different sized pixels, and if they all have the same read
noise (per pixel), then the only difference between the binned pixels
is that the effective read noise in the binned pixel is n times larger
(if I binned n pixels), I don't think anybody disagreed. I ignore fill
factors here (ie take them to be unity).

Without retyping every single thing I have typed in this thread
(obviously nobody cares about it), your argument seems to be that this
means that we'll always get better performance from larger pixels.
That's true, and obviously there's a lower bound to read noise/pixel,
and this sets a lower bound on the effective pixel size (this will
depend on a threshold I set for acceptable low illumination
performance).

But I find it very hard to believe that this limit is at 6 microns, or
that the performance of the canon cameras in terms of read noise
cannot be duplicated and improved. So I don't understand everybody's
reactions to this idea (on the other hand, they do not surprise me).
Yes it's a tradeoff between low light performance in that for given
read noise we'll get better performance with larger pixels, although
nowhere near the extend to which this is done now with small pixel
cameras. The low light performance can be improved by lower read noise
and larger pixels (obviously!), so it is a tradeoff, in the end, and
for low enough read noise we can approach the performance of larger
pixels (as you said, the only difference is a term in the noise of
n*r, with n^2 the number of binned pixels and r the read noise/pixel).
Nobody is arguing that we want 1nm^2 pixels here, so we're not dealing
with a physical limit.

Look, if I met you in 1984 at a conference (so in a technological
mood :) ) and told you that in 22 years you'll be able to buy a 5D or
a D200 for less than 2000 euro/dollars (or even a p&s for 100 euro),
what would you say? Remember, even AF cameras were novelties then. My
point is that your arguments are basically based on current
technology, not fundamental limits, except when talking about extreme
low light performance (a few electrons/pixel). And it's not as if
we're talking about something as extreme as a detector requiring .4K
to work, we are discussing reducing read noise at low gains. I am sure
it is not trivial to do, but that's another story.



>
> If you want to try the experiment with current cameras, use an
> ISO where the DSLR is not electronics limited, like ISO 800.
> You'll see that the small pixel camera can actually come close
> in binned images quality, but noise AT BEST at the low end will be worse
> by square root number of pixel binned. Fill factor using edge
> effects will actually make the small pixels worse overall.
> How much worse depends on a number of factors, all quite predictable
> if we knew what the parameters were (like the fill factors).
>
> Then in the real world, you earlier complained about fixed pattern noise.
> The practical problem with your idea is that for the small pixel
> camera to compete with the large pixel camera, the fixed pattern
> noise would have to be considerably less than the fixed pattern noise
> in the large pixel camera, by at least the square root of the
> number of pixels being binned (depends on the spatial frequency distribution
> of the fixed pattern noise).
>
> So, again, I resent you saying my data are wrong when you are applying it
> to theoretical cameras that do not exist. My data and conclusions
> are absolutely right for evaluating current cameras that DO EXIST and
> that people are trying to choose and understand the differences between such
> real cameras.

I don't think he said it's wrong, he disagreed with your conclusions.

>
> Roger


From: John Smith on

"ipy2006" <ipyasaswi(a)gmail.com> wrote in message
news:1173274977.039356.148330(a)h3g2000cwc.googlegroups.com...
> On Mar 7, 7:58 am, ASAAR <cau...(a)22.com> wrote:
>> On 7 Mar 2007 04:03:00 -0800, Yip quipped:
>>
>> > I have to shoot action photos in low light conditions. What is the
>> > best DSLR for this purpose?
>>
>> It's never just a matter of getting the best DSLR for the purpose.
>> It's a DSLR body + lens combination that must be considered, as well
>> as the low light level and specific types of actions you need to
>> shoot. Some combinations will be so demanding that there may not be
>> a suitable solution. Others may be so easy that almost any DSLR
>> will do. If you can determine the minimum gear that will suffice,
>> you can save a lot of money buying a body and lens(es). If you
>> don't know but have enough money to burn, you could start with a
>> Canon 5D and see if that and a typical "kit" lens gets you what you
>> need. If not, you might need to spend about $1000 or even several
>> thousand dollars getting a better lens if the kit lens proves
>> inadequate. If your sports shooting demands long bursts of shots at
>> very high frame rates, you might need to get a much more expensive
>> body than the 5D, ie, one of the "pro" bodies from Canon or Nikon.
>>
>> You gave no information at all as to the kind of action photos
>> you'll be shooting or in what kind of low light levels. If you can
>> tell us what they are, you might get some concrete examples of what
>> kind of DSLR will meet your needs. Which brings up another point.
>> You really want to know what kind of cameras will be suitable. You
>> don't want to ask what the BEST DSLR is, because the "best" for one
>> person won't be the best for another, and the absolute "best" for
>> *you* might be $8,000 above your budget, whereas a $1,200 camera
>> with kit lens might do everything you're looking for, and would be
>> good enough. Care to share which camera(s) you're currently using,
>> if any?
>
> Here are some scenarios,
> Indoor shooting of people talking with hand gestures, people walking
> or pacing in the room, kids playing, women cooking in kitchen, or
> groups of people in meeting rooms etc. Sometimes I don't have the
> ability to use lights, I need to depend on flash and high brightness
> setting. Currently, I am using a Sony Digital Camera, Cyber-shot, DSC-
> H2. My budget is $1000 and at the most $1500.

When you say "hand gestures" you mean they get angry if you use a flash or
other additional light source?

Sounds like you're going to be working in a confined area. If you don't need
the long reach of a zoom, you might want to consider something like the
Nikon D40, throw away the kit lens, and buy a 50mm 1.8 (about 100$give or
take) Nice fast lens, and the camera is getting good reviews for higher ISO
shootin'.

I'm going to order one myself tomorrow night.

DP




From: Paul Furman on
Roger N. Clark (change username to rnclark) wrote:
> John Sheehy wrote:
>
>> 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.
>
>
> John, you are confusing several things in your argument in this thread.
> 1) Small pixel size cameras are at near unity gain at low ISO.
> (for other readers, unity gain ISO is the ISO where 1 electron
> equals one bit in the A/D converter).

Aughhhh, I hate that I can't understand these discussions.

Unity Gain ISO - the ISO where 1 electron = 1 bit in the A/D converter

A/D Converter - analog to digital, where electrons are assigned numbers

So unity gain ISO is where there isn't a rounding error problem.
Read Noise is the rounding problems, higher bit depth in the raw file
lessens read noise.

P&S cameras don't have this problem because there are so few electrons,
they are easy to count?

Does it really matter if there are minor rounding errors? Is it really
noise because colors are off by 1 bit? Relevant noise is random wack
hair-brained colors, not minute color shifts, right?

What is Dark Current?

What's this business of clipping at blackpoint before setting gamma?
That means you can set the blackpoint? How could there be negative
number? Why?

I don't get the charts against pixel pitch. It doesn't matter because
there could be some efficiency or inefficiency in the layout, the only
thing that matters is full well electrons, right?

Signal to Noise seems clear enough, shoot a gray card & count the pixels
that come out some color other than gray.

What is the significance of raw noise versus final bayer interpolated
RGB values unless you are doing binning to interpolate by greatly
shrinking the pixel count? (if I understand the term 'binning' correctly)

And who cares what the characteristics are before white balancing?
Nobody is using un-whitebalanced images and the basic WB is fairly
dramatic in any lighting. I can see how these things make the math clean
but I don't see how they are necessarily relevant in the final product.

Ah, my head hurts... am I understanding?


> ISO's above unity gain
> ISO is nothing more than "digital ISO." You essentially gain
> nothing at higher ISOs as you can't measure a fraction of an electron.
>
> 2) Current DSLR cameras, like the Canon 20D, Nikon D50, and all other
> DSLRs tested on my web pages and other people testing cameras
> that I reference, ARE NOT SENSOR READ NOISE LIMITED AT LOW ISO.
> You cite the high read noise of DSLRs at low ISO in electrons,
> but that is an electronics limitation, NOT sensor limitation.
>
> 2a) As electronics improve, e.g we see that in the newly announced
> canon 1D mark III with 14-bit converter, the low ISO noise
> is reduced (according to Canon). Current scientific sensors
> use 16-bit converters and achieve full well digitization with
> good digitization of true sensor read noise. We'll see that
> soon in coming DSLRs.
>
> 3) So what you are describing as lower read noise for binned small
> pixel sensors, is really because the small pixel cameras are operating
> at near unity gain ISOs, while the DSLRs are not. You are comparing
> apples and oranges. (Interesting that DSLRs are not yet living up
> to their low ISO potential! That is exactly what is shown in Figure
> 4 at
>
> http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary
> where the P&S small sensors are below the 12-bit line and the DSLRs are
> above the line indicating they are A/D electronics limited. Note the
> data indicate the 1D Mark II and 5D would still be limited with 14-bit
> converters, so the new 1D Mark III will still not quite live up to its
> potential.)
>
> 4) DSLRs do not live up to their full low signal, low ISO potential
> because they
> are A/D limited. Remember, all A/D conversions are accurate to +/- 1
> bit.
> A DSLR with 50,000 electron full well (e.g ~ Canon 20D) and a
> 12-bit converter digitizes 1 bit = 50000/(2^12 -1) = 50000/4095 =
> 12.2 electrons.
> 14-bit converter digitizes 1 bit = 50000/(2^14 -1) = 50000/16383=
> 3.05 electrons.
> The read noise of the 20D sensor is 3.9 electrons. 14-bits is close to
> digitizing that well but 12-bits is not (remember the +/- 1 bit added
> noise).
>
>
> > Lionel <usenet(a)imagenoir.com> wrote in
> > news:85vmv2ttgd09e4c6gq47mkrojj5pbme1kq(a)4ax.com:
>
>>>> 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.)
>
>
>> John Sheehy 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*.
>
>
> The current crop of available cameras gives choices like:
> 8 megapixel P&S small sensor, small pixel camera versus
> 8 megapixel DSLR with large pixels. I provide data and information
> for people to evaluate what they would lose in making a choice
> between such cameras. THAT IS NOT WRONG.
>
> For those new to my web sites, relevant web pages are at:
> http://www.clarkvision.com/imagedetail/index.html#sensor_analysis
>
> John, your assertion seems to be (correct me if I'm wrong):
> Given two sensors of the same total size, one with large pixels,
> and one with small pixels, the small pixel camera can deliver
> equal quality images when the pixels are binned to the
> size of the larger pixels. You then support this by saying
> the low ISO read noise of DSLRs is larger than at high ISOs
> and at low ISOs is larger than small pixel cameras.
> You bolster your argument using currently electronics limited
> DSLRs with fictitious small pixel sensors that have many times
> the pixels currently available in any sensor (e.g. your 223 megapixel
> sensor or something like that).
>
> So with the fact that current 12-bit DSLRs must be limited in their
> read noise at low ISOs and the fact that 16-bit scientific sensors
> available (even amateur astronomers have such chips), it is a
> matter of time before we see the DSLRs with lower effective read noise,
> e.g. as is the case with the new 1D Mark III.
> So, I think you should level the playing field and use true sensor
> read noise in your calculations. When you do, you'll find this
> is a common sampling problem and is encountered in science all the
> time. The noise in any one measurement has an error. The smaller
> the signal, the lower the signal to noise ratio of that measurement.
> Adding multiple samples improves as the square root of the number
> of samples.
>
> So in the level playing field of equal read noise in both large and
> small sensor, the small sensor binned up to the large sensor will have
> read noise higher by the square root of the number of pixels binned.
>
> If you want to try the experiment with current cameras, use an
> ISO where the DSLR is not electronics limited, like ISO 800.
> You'll see that the small pixel camera can actually come close
> in binned images quality, but noise AT BEST at the low end will be worse
> by square root number of pixel binned. Fill factor using edge
> effects will actually make the small pixels worse overall.
> How much worse depends on a number of factors, all quite predictable
> if we knew what the parameters were (like the fill factors).
>
> Then in the real world, you earlier complained about fixed pattern noise.
> The practical problem with your idea is that for the small pixel
> camera to compete with the large pixel camera, the fixed pattern
> noise would have to be considerably less than the fixed pattern noise
> in the large pixel camera, by at least the square root of the
> number of pixels being binned (depends on the spatial frequency
> distribution
> of the fixed pattern noise).
>
> So, again, I resent you saying my data are wrong when you are applying it
> to theoretical cameras that do not exist. My data and conclusions
> are absolutely right for evaluating current cameras that DO EXIST and
> that people are trying to choose and understand the differences between
> such
> real cameras.
>
> Roger
From: John Sheehy on
Doug McDonald <mcdonald(a)SnPoAM_scs.uiuc.edu> wrote in
news:eth4fs$o8k$1(a)news.ks.uiuc.edu:

> John Sheehy wrote:

>> Of course not, but many people believe so for capturing photons
>> instead of raindrops!

> That last sentence is WRONG. That said, it is wrong only because
> of read noise, which is of the order of 3 to 5 electrons.

This was a thought experiment, to isolate the shot noise issue. People
are always saying that smaller pixels means more shot noise. That is
what this was about. Read noise is another subject, but the fact is,
read noise in the real world decreases with smaller pixels, either in
binning, downsampling, or considering noise power as a function of
magnification.

Read noise is 2.7 electrons in my FZ50 at ISO 100. 9 of those pixels
binned together equal a typical DSLR pixel both in coverage area, and
maximum photon count. 2.7 * 9^0.5 = 8.1 electrons of read noise for the
"superpixel". That's about 1/3 of the ISO 100 read noise on my 20D.

> If the
> actual signal is bigger than say 100 photoelectrons the read
> noise becomes negligible. Nevertheless, at the very lowest signal
> levels, your argument is wrong in the real quantized world.

What are you comparing it against? Let's say you have 9 tiny pixels with
a signal of 5 electrons, and a read noise of 2.7 electrons. 9 of those,
binned together, have a signal of 45 electrons, and a read noise of 8.1
electrons. With hardware binning like Dalsa uses, that might mean 2.7
electrons (or a tad more) even for the binned superpixel. A typical DSLR
at ISO 100 will have a read noise of 18 to 30 electrons.

Large pixels are not doing well in current technology, in terms of read
noise at low ISOs!

The real world does not match your boogey-man stories of read noise
problems with small pixels.

--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS(a)no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
From: John Sheehy on
Lionel <usenet(a)imagenoir.com> wrote in
news:th5ov295p0jqsusgd41eolo2dvpkr6i97d(a)4ax.com:

> Exactly. And he's also neglecting to account for (in his analogy), the
> drops that hit the lips of the smaller containers, & are lost,

Apparently, not many photons are lost with the 1.97u pixel pitch in my
FZ50. It captures almost exactly the same amount of photons per square mm
at ISO 100 saturation as the 1DmkII! Even photons that get close to the
edge may still go into a well, whether it is the next one over is
irrelevant, as the resolution is still more precise than if you had large
pixels, where any collected photon could have been in any of a number of
pixel wells on a finer-pixel-pitch sensor.

You're talking boogey-men. Talk facts, from real world stuff, please. No
cultish hand-waving.

> (equivalent to the extra fill-factor loss), & the fact that the
> smaller containers will fill & overflow more easily at points with
> heavy exposure (which is equivalent to lowered well capacity in the
> smaller photodiodes, thus a reduced maximum photon capacity).

You're getting very funny now. Go back and look at what you just wrote;
you just complained about resolution!

What if there was a pattern of extra drops in every second row of small
containers? How would you see that with the larger containers?

--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS(a)no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><