From: John Sheehy on
Paul Furman <paul-@-edgehill.net> wrote in news:r8Ofk.16605$89.6967
@nlpi069.nbdc.sbc.com:

> Why does base ISO matter?

Because that is where people shoot when they want maximum DR, or
footroom, at least, when they have ample light?

> Sure, but if you have bright highlights also, the small pixels
> are badly
> crippled.

How so? Smaller pixels can keep more highlight detail, like film,
because the higher shot noise in each pixels guarantees that a percentage
of pixels will not clip when the mean clip, so levels above the clipping
point can be discerned at reduced resolution.

> The sample shot does have bright areas but as I
> understand, it
> was severely underexposed. Can you explain a little more clearly about
> these factors please:

> Shot noise -

Shot noise per unit of area is lower in the FZ50, for a given exposure.
It has one of the highest QEs in the industry. Per pixel, the 400D
collects up to about 43K photons 4 stops above metered middle grey, the
FZ50, about 4800 photons 2.5 stops above metered middle grey. 4800*
83.521 = 40,090, so the FZ50 sensor collects a maximum number of photons
per unit of area slightly less than the 400D. The FZ50 captures those
40,090 photons with 1.5 stops less exposure than the 400D, though, so it
has an area-based shot noise of about 0.7 stops less than the 400D, for
the same exposure. It is a general trend in current sensors that the
tiny pixels in P&S sensors have from 0.5 to 1.5 stops more area-based
photon sensitivity than DSLRs (closer to the 0.5 for more recent DSLRs).

> Read noise -

Read noise per pixel is about 2.8 12-bit ADU in the FZ50, and about 1.65
12-bit ADU in the 400D, both at ISO 100. Scaled by pixel pitch, the read
noise of the FZ50 is about 2.8/2.89 = 0.97 ADU, in 400D pixel terms. And
that's not even including the fact that the FZ50 is 1.5 stops more
sensitive in RAW numbers (not that this would affect DR, but it does
affect real sensitivity).

> Full well capacity -

Covered in "Shot noise".

> I sort of vaguely can imagine the possibility that the noise may be
> better due to the math when it all works out in the real world
> (perhaps)
> but a larger pixel should absolutely have more dynamic range: that is
> real simple math.

No, it is not. DR would be directly proportional to the photon count at
saturation at any given ISO, at the pixel level, *if* there was no other
noise than shot noise. There is read noise and all its associated post-
read noises (and dark current noise when applicable), which lowers the DR
of individual pixels, and the DR of an image is *NOT* the DR of a pixel;
that is one of the biggest pieces of nonsense propagated as obvious
truth.

> And of course an 85MP AP-S sensor is going to cost a heck of a lot of
> money, but yeah, lets just say we want the best possible image for this
> comparison.

The extra cost would mainly be for the parallelized readout to keep read
times and noise down. Higher pixel density on the sensor itself is not
more expensive; the bigger the pixels are, the more likely a sensor will
need to be discarded with a defect, because the defect will affect a
larger percentage of the imaging area.

--

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John P Sheehy <JPS(a)no.komm>
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From: ASAAR on
On Thu, 17 Jul 2008 22:15:06 GMT, John Sheehy wrote:

>> If the FZ-50 really has some kind of noise advantage at ISO 100
>> over Canon's DLSR it would be useful if he could demonstrate it
>> using real images, and to the extent possible, with both cameras
>> filling their sensors with the same image.
>
> That makes no sense at all. I am not comparing cameras;

Only because sense can't penetrate your thick skull. People don't
buy sensors. They buy and use cameras. If you can't show that your
warped theory provides any real world benefit, you may want to
examine why that is so. BTW, what you failed to understand is that
the direct comparison would be between the images, not the cameras.
See above . . .


>> What Sheehy has done instead is to compare portions of each sensor
>> having the same actual area.
>
> That is the only way to compare pixel density, which is the only thing I
> wish to demonstrate here.

I hate to break it to you, but you're demonstrating much more than
you realize.


> I don't start threads to state the obvious.

They are obvious because the threads are all rehashes of what
you've previously posted. Unconvincing before, unconvincing now.


> The big myth going around today is that "cramming" more pixels
> into a given sensor size deteriorates image quality, and that is
> generally nonsense.

Your nonsense continues. Consider DPReview's conclusions about
your pet FZ50. They admitted that it had "excellent resolution",
and "under the right conditions it produces superb output." It
seems that the myth creator is *you*. DPReview recognizes what you
apparently can't, that cramming too many pixels into the sensor
increases that probability that more inferior images will be
produced because conditions aren't always optimal.

If everything you say about pixels evaluated for noise and DR at
low ISOs is true, it still doesn't matter if you can't show how that
will help people to select a camera that produces superior images.
This conclusion is far clearer and far more helpful for that purpose
than anything you've ever written.

> Producing a camera this size with 35-420mm (equiv.) F2.8-3.7
> zoom lens means you have to use a small sensor, and small
> sensors mean compromise because noise is always going to be
> an issue. I completely understand why Panasonic chose to jump
> from 5 to 8 to 10 megapixels in three generations of its flagship
> FZ camera - it's a lot easier to sell a camera on pixels than
> picture quality, and the average consumer (and it must be said
> the average camera store buyer) uses megapixels above all else
> when sorting cameras into categories. Panasonic's marketeers
> knew full well that with 10MP 'consumer' SLRs on the horizon
> (and 10MP the new high end for compacts too) the FZ50 needed
> a headline 'resolution' that kept it near the top. I do, however,
> think it was a mistake to think that the FZ50 buyer is the 'average'
> consumer, unable to base decisions on anything but megapixels...
>
> And so what we have is a camera that stretches its sensor to
> almost breaking point and compensates for the lack of sensitivity
> in anything but the brightest conditions by using excessive noise
> reduction. The FZ50 is an excellent 5 or 6MP camera, but a
> rather less impressive 10MP camera. Is this a problem? Probably
> not - by the time the huge files have been shrunk down for
> printing or viewing on-screen they look fantastic, and the
> handling and features are quite simply peerless. But do not, for
> a minute, think that the 10 million pixels you're getting with the
> FZ50 bear anything but a passing resemblance to the 10 million
> pixel images you'll get from a good SLR once you get above
> ISO 100, or once light levels start to drop.
>
> . . .
>
> And so, to sum up; for the serious user the FZ50 is without doubt
> the best equipped, best specified and best handling 'bridge camera'
> on the market today, and under the right conditions it produces
> superb output. It is a rewarding and enjoyable photographic tool
> that - once you've learned its quirks - offers a compact 'all-in-one'
> solution to anyone wanting a huge zoom range without all that lens
> changing and all that bulk. Inevitably this involves a certain amount
> of compromise; the smearing of fine, low contrast detail that is the
> hallmark of the Venus III engine limits the FZ50 to low ISO settings
> for any serious photography unless you're happy to accept that
> you'll never be able to produce big enlargements. For me this is an
> acceptable compromise, and - though I wish Panasonic would drop
> the megapixel race and concentrate on picture quality - it does
> produce excellent printed results. If this had been a mould-breaking
> 5 or 6 megapixel with excellent low noise performance throughout
> the ISO range (and particularly up to ISO 800) it would no doubt
> have performed considerably better and would have been an easy
> choice for a Highly Recommended. As it is it just squeezes in thanks
> to its many other outstanding qualities - and only for those users
> who can live without anything over ISO 200.

http://www.dpreview.com/reviews/panasonicfz50/page19.asp

From: John Sheehy on
notvalid(a)yahoo.com wrote in news:7hku74p4pqa0rtihqoc3iel1viced2s07o@
4ax.com:

> Unfortunately, there are far too many variables that have been changed
> in your two test subjects to make any real conclusions about the
> pixels.

The only thing different is the pixels and the lenses; the pixels are
*supposed* to be different, and the lenses have to be different in
comparing such different pixel pitches by necessity, as there are no
common lens mounts for small and large pixel cameras. But seriously, ow
sharp do you think a 5.7 micron image can be, next to a 1.97 micron
image? Even if you had the sharpest lens available, you couldn't compete
with the potential of the smaller pixels.

> There is no such thing as "all things being equal" in your
> tests, because virtually nothing is equal.

Give me a break; this is closer to being equal than most every other test
I have ever seen by anyone else. The lenses are the only unwanted
variables here, and as I said, even the sharpest is going to turn to mud
compared to smaller pixels.

> You have compared two test *systems* and that's all that can really be
> claimed with any validity.

I am comparing one camera that almost everyone agrees is horrible because
of its high pixel density, to another much more respected for its lower
pixel density, and showing that the nighmare doesn't happen, because of
pixel pitch. If you don't find that significant, I don't know what to
tell you.

I really wish I had a D3 or a 1D3 to do this with, instead of the 400D,
but the 400D is the best DSLR I have in terms of read noise per unit of
area at ISO 100. The D3 and 1D3 I would expect to under-perform the 400D
in read noise, and outperform it slightly in shot noise, and underperform
in terms of resolution.


> But with that premise, I don't think that
> the conclusion you're trying to form is valid. You may be able to
> make quality comparisons of final printed output.... depending on how
> you conduct that test (and your current testing method doesn't lend
> itself to making a valid comparison of final printed output).

Why would you expect the relative noise/detail to be any different in
print? Does printing suddenly make one image better, which was inferior
on the monitor?

> Data collection is a crucial part to any mathematical/statistical
> analysis. And the data collection performed for this test are far too
> restrictive for any statistical significance; and cannot really be
> used to draw any general conclusions.

Regardless of what it says or doesn't say about pixel density
universally, it does say that the pixels in the much-maligned FZ50 have
less noise and are capable of more detail in the deep shadows of ISO 100
than the pixels in the 400D, and that is EXTREMELY significant in light
of all the myths about pixel density.


--

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John P Sheehy <JPS(a)no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
From: ASAAR on
On Thu, 17 Jul 2008 21:09:14 GMT, John Sheehy wrote:

>> I was on your side for the most part originally but sorry to say
>> you've lost me. I just hope you are not in science because this
>> is NO way to run an experiment.
>
> This is the best possible way to run this experiment, as there are no
> possible pairings out there of cameras with the same mount and the same
> size sensors with vastly different pixel densities of the same era.

How about Nikon's 6mp D40 vs. the 10mp D40x? Or Canon's A610 vs.
A620? Announced at the same time, they used the same size 1/1.8"
sensors, where the former had 5mp vs. the latter's 7mp. There are
more such pairings, but I'd be surprised if you'd accept any of
them, as they wouldn't aid your agenda.

From: ASAAR on
On Thu, 17 Jul 2008 20:37:49 GMT, John Sheehy rewrote:

>> Anyone with any amount of experience in these matters would recognize
>> that even a magic lens with no softness of any kind
>
> Sorry, I hit send before I finished that post. It should have read "Anyone
> with any amount of experience in these matters would recognize that even a
> magic lens with no softness of any kind would pale next to the FZ50 lens
> and pixel density here, using the 400D and scaling 289%.

Sorry, but that doesn't make as much sense as the original.


:)