From: John Sheehy on
Steve <steve(a)example.com> wrote in
news:99t384ljpcrq8nu2r2p52kosv71bt21egs(a)4ax.com:

> If all you claim to be measuring is resolution at the focal plane then
> why are you even showing pictures of anything at all? It's pretty
> obvious that higher pixel density has more resolution at the focal
> plane.

Of course, if the lens can supply it. The noise is the most significant
thing to me, and the main reason I made this demo. The resolution is
just a confiormation of the obvious.

> Of course, that measure is completely meaningless to any real
> world normal photographic application.

How so? If you're cropping an image or printing the whole thing large,
less noise in the shadows and more detail is not of value?

It only is meaningful for
> specialized applications where one is purposefully trying to image
> something projected onto a very small focal plane. For real world
> photographic applications, you have to take the entire sensor size
> into consideration also, since that's what the camera is imaging onto.

I never implied otherwise, but it is the sensor width or height factored
by the quality per unit of area that determines overall image quality.

>>measuring something else. FOR THE SEEMINGLY MILLIONTH TIME: I AM NOT
>>COMPARING CAMERAS OR SENSORS. I AM COMPARING HOW DIFFERENT PIXELS
>>RECORD A GIVEN AREA OF FOCAL PLANE, WHICH IS WHAT MATTERS MOST WHEN
>>DISCUSSING "PIXEL DENSITY". Comparing a 12MP 1/2.5" sensor's image to
>>that of a 12MP FF with the same field of view is *NOT* a comparison of
>>pixel density. It is a comparison of full images from different
>>sensor sizes,
>
> Actually, that *IS* comparing pixel density. Because that's the only
> thing different between the two sensors.

Nonsense. Their sizes also vary! How can you trivialize that? That's
ridiculous.

> The total number of pixels
> is the same, the image falling on them is the same, etc. etc.... The
> only thing different is the pixel density,

NO! The sensor size is different, *and* the pixel density is different.
How can you be this blunt?

> and that is what you're
> trying to compare. In your test, you are not keeping the total number
> of pixels that capture the image the same.

They're not supposed to be! It would be a different test if I were!

What is this obsession with so many posters to make me demonstrate/test
something else rather than what I set out to do. It's almost as if
people are so stupid as to think that I am doing this to make some proof
of a monolithic superiority of the FZ50 IQ over the 400D. Any such
person is seriously illiterate, to put things bluntly.

> So you are comparing more
> than just pixel density, you're also comparing resolution.

No; I'm sorry, you're going to have to change your terminology. "pixel
density" without any qualifiers refers to pixels per unit of area, and
has nothing to do with how big an area the sensor has. Without any
mention of sensor size, or total pixel count, pixel density only
references sensors of the same size, or crops of the same physical size
on the focal plane, or area-based performance.

> And in
> your resolution comparison, you are severly handicapping the 400D by
> upscaling it 3 times more than the FZ50.

That's how big the pixels really are, absolutely, on the focal plane! I
can not compare the effects of pixel density without doing this!

>>with the same number of pixels, which happen also to have different
>>densities.

>>> I don't think anyone
>>> is going to argue that higher pixel density gives better resolution
>>> at the focal plane. But that is absolutely meaningless if the size
>>> of the sensor is different.
>>
>>Pixel density is discussed concerning sensors of the same size. There
>>ARE NO SENSORS OUT THERE THAT ARE THE SAME SIZE WITH 2 MICRON AND 5.7
>>OR 8 MICRON OR GREATER PIXELS THAT CAN BE COMPARED, so we have to
>>compare the same area from cameras with vastly different pixel
>>densities, AND sensor size, to extrapolate what a large sensor with
>>high pixel density might do, compared to the low pixel density that
>>larger sensors now have.
>
> There are plenty of cameras out there with the same size sensor and
> pixel densities that are as different as what you're comparing. The
> fact that doing so disagrees with your results shows that your
> extrapolation is not a valid one.

Name some? If you really have any, you have a P&S sensor with 2 or 3 MP
from yesteryear. Get me the RAWs from 2 of them, same Av and Tv values,
same real focal length (which equates to same FOV with same-size
sensors), of the same scene in the same lighting, with shadow detail.

>>So why the hell are you and all the rest of the peanut gallery
>>replying to my posts, if this doesn't interest you? Do you burst into
>>churches on Sunday morning to anounce that their religion doesn't
>>interest you? Do you go to sporting events to protest people's
>>interest in sports? So why, then, do you fell a need to come here in
>>this thread and tell us that the subject matter is irrelevant to you?

> Maybe because I have a special application that requires greater pixel
> density and a small sensor? But I know for absolute certainty that my
> camera with higher pixel density is noiser with less DR than the one
> with lower pixel density. However, the small sensor camera

Oh, just a trivial detail, isn't it, the difference in size?

> still
> works better than the large one for afocal astronomical photography.
> But not for anything else I've ever done.

That's because you're using the entire FOV perhaps, and are dependent
upon *SENSOR SIZE*, which is independent of PIXEL DENSITY. The two are
separate factors that determine overall image quality; not synonyms.

>>> The measure of resolution the
>>> rest of us care about is the resolution of the image captured by the
>>> entire sensor.

> The problem is that your test is not testing what you claim it is. You
> are purposefully handicapping the low pixel density sensor, both in
> terms of resolution and in terms of not taking advantage of it's full
> DR, just to prove a point. That's not a valid test. It's a
> hypothesis where the test is skewed to come to the conclusion that the
> tester wants. That happens all the time, usually by testers with an
> agenda which you obviously have.

It matters not one iota whether or not I have an agenda, as I have not
hidden anything. The real absolute exposure and focal length is the same
(within the tolerances of the cameras). The only difference is the pixel
structure on the focal plane, and the lenses used. Anyone with half a
brain would realize that there is no chance for the 400D to have the same
resolution in absolute MTF, as the lower pixel pitch BY DEFINITION means
that the Nyquist is at 35% the frequency of the nyquist of the FZ50
pixels. The room for improvement in the 400D pixels with a sharper lens
is extremely marginal. Take *ANY* sharp image you can find, anywhere,
take a crop of it, and upsample it to 289%. Can't compete with the FZ50
pixels here (other than that you might have less noise in the image that
you chose).

>>> I.e., if you have two 10MP
>>> sensors of different sizes, the only real world meaningful way to
>>> measure noise and DR vs. pixel density is to allow both 10MP sensors
>>> to capture a similar scene across the entire sensor and then compare
>>> the results at 100%.

>>Nonsense. That is a test of SENSOR SIZE, not PIXEL DENSITY.

> Nonsense. That is a test of pixel density. Since the pixel density
> is what determines the sensor size for a given number of pixels. If
> you don't keep the number of pixels the same, you are testing
> something more than pixel density. If you want to take SENSOR SIZE
> out of the equation and truly measure only PIXEL DENSITY, then you
> have to compare the same sensor size since it's obvious that your
> extropolation doesn't work. And the main reason your extrapolation
> doesn't work is that you are blowing up the low density camera to over
> 100% rather than shrinking the high density camera to less than 100%.

I did BOTH. The insets are at the native pixel resolution of the 400D,
and the FZ50 crop downsampled slaughters it.

> If you did your test that way, you'd have a better chance of your
> extrapolation giving valid results. That still doesn't solve the
> problem you're having with only using a small portion of the low
> density sensor's available DR though.

That's because I am not concerned with the full images. I am interested
in the quality PER UNIT OF AREA as affected by PIXEL DENSITY.

>>I've given far more than just a hint of what I am demonstrating here,
>>yet almost no one who has responded seems to understand. My thoughts
>>are going way over your head, apparently.

> Not at all. I know exactly what you're trying to show. The problem
> is that your test is flawed in several severe ways and is designed to
> give the results you're after. That is not a valid scientific test.

Not a valid scientific test of WHAT? I have no evidence that you even
understand what I am testing, because I *AM* testing it, and the FZ50
pixels are clearly better at it. And where are the valid scientific
proofs that oppose what I am demonstrating?

I did show that an APS-C sensor filled with FZ50 pixels would give more
absolute sensitivity and footroom than the pixels that are currently in
the 400D, which has one of the lower base-ISO read noises per unit of
area in the DSLR world. I would much rather have done it with a D3 or a
1D3, but they are not available to me. I made no claim directly about
better DR, and stated that the 400D still has a stop more headroom, with
the same real exposure, because the FZ50 has about double the quantum
efficiency of the 400D (and has about 1/2-2/3 stop more than the best
DSLRs). A DR test to parallel this sensitivity test would require me
using a longer exposure for the 400D, and I would have to measure exactly
how much. The image-level read noise in the 400D crop I supplied is
easily a stop worse than the FZ50 noise, so expect the FZ50 pixels to be
as good or slightly better for DR.


--

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John P Sheehy <JPS(a)no.komm>
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From: John Sheehy on
John O'Flaherty <quiasmox(a)yeeha.com> wrote in
news:ggt284dgvdc3t0jc9f1qo0pq38pgm4dvfb(a)4ax.com:

> On Sat, 19 Jul 2008 04:39:21 GMT, John Sheehy <JPS(a)no.komm> wrote:
>
>>John O'Flaherty <quiasmox(a)yeeha.com> wrote in
>>news:8lh2841k4vmfcdt6u1qgdv1tkokactlbne(a)4ax.com:
>>
>>> I did try measuring an area of the sky (which presumably has uniform
>>> illumination) in photoshop histogram, and found a pixel level of
>>> about 45 and a standard deviation of about 22, on both magnified
>>> images. Does that mean an equal p-p noise level, but with the noise
>>> on the higher resolution image at higher spatial frequencies?
>>
>>You can't directly take the standard deviation of an upsampled image
>>to gauge noise; it is meaningless, because standard deviation is only
>>meaningful as an indicator of pixel-level noise when the noise
>>spectrum is concentrated at the nyquist. When you have different
>>distributions, then the noise is in different frequencies, and
>>frequency is everything with noise. That is why I am emphasizing the
>>visual here.
>
> The reason I made the measurement was that the color variation
> appeared the same to me, visually, in the two enlargements; the
> measurement confirmed what I saw. In the non-enlarged frames, of
> course the finer image shows less noise, because it is filtered out,
> by the eye or by the display device. I don't see how subjective
> perception of noise can be separated from resolution. Is your test
> intended to show a subjective effect, or something quantitative?

I am showing the visual, and I hope that it also shows that standard
methods of quantitative noise measurements are faulty. Standard
deviation alone is missing a factor or factors, in the noise equation.

You can clearly see that at 100% pixel view for both cameras, that the
FZ50 has more pixel noise. It always has less visible noise, however,
when both crops are scaled to the same size.

I consider there to be three basic qualities; PQ (pixel quality), IQ
(image quality), and SQ (subject quality). What I call PQ, many people
seem to use as the gauge for "IQ". SQ is very important, too, because if
we are shooting a subject, the quality of the subject scaled to a fixed
subject size is also important, especially in the subjective realm. You
could have *exactly* the same SNR curve at the pixel level of two images
presented at the same size from the same number of pixels, and the noise
could be more troublesome in one than another. Imagine one was a group
shot of 100 people, and the other was a full-frame portrait. You will
notice the noise far more in the group shot, because the noise grain is
large compared to the size of the faces, while the same pixel/image noise
on the full-frame portrait might still allow amazing facial detail.

SQ is the main quality concern, too, when I use a TC. Many judge the
value of a TC by the IQ or PQ, which is folly, IMO. You must judge by
SQ, since if you're willing to zoom in like that, then your sesired
composition is one that would force you to crop and have less subject
resolution and larger nosie grain without the TC.
--

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John P Sheehy <JPS(a)no.komm>
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From: John Sheehy on
ejmartin <ejm_60657(a)yahoo.com> wrote in
news:78b598a9-8c74-452c-8524-102b423f54f9(a)34g2000hsh.googlegroups.com:

> Well, that's the tradeoff isn't it? At least, that's the tradeoff for
> current implementations at high ISO, where it's the sensor properties
> that control DR -- big photosites for more sensitivity in shadows, or
> small photosites for more resolution. At low ISO, due to the
> limitations of current implementations in the ISO amplifier/ADC, one
> actually does better per unit area with small photosites, because they
> place less demands on the dynamic range of that downstream
> electronics. Small photosites will be better at low ISO until camera
> companies start delivering all the DR that the sensor is offering.

Of course, if we take that all the way, and exclude read noise
completely, the high-density camera still wins in resolution, with the
same image-level noise (shot noise). And from the look of things, at
least for the near future, tiny sensors can have higher QEs, so it is
possile that the smaller pixels can outperform at a given exposure level,
unless the relatively poor QEs of big pixel cameras are rectified. A lot
depends on the "why" of the higher QE for the higher pixel densities.

Let us not forget that the base ISO of the FZ50 is labelled "100", but it
is really 200 pulled a stop, in DSLR terms.
--

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John P Sheehy <JPS(a)no.komm>
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From: ejmartin on
On Jul 19, 1:08 pm, John Sheehy <J...(a)no.komm> wrote:
> ejmartin <ejm_60...(a)yahoo.com> wrote innews:78b598a9-8c74-452c-8524-102b423f54f9(a)34g2000hsh.googlegroups.com:
>
> > Well, that's the tradeoff isn't it?  At least, that's the tradeoff for
> > current implementations at high ISO, where it's the sensor properties
> > that control DR -- big photosites for more sensitivity in shadows, or
> > small photosites for more resolution.  At low ISO, due to the
> > limitations of current implementations in the ISO amplifier/ADC, one
> > actually does better per unit area with small photosites, because they
> > place less demands on the dynamic range of that downstream
> > electronics.  Small photosites will be better at low ISO until camera
> > companies start delivering all the DR that the sensor is offering.
>
> Of course, if we take that all the way, and exclude read noise
> completely, the high-density camera still wins in resolution, with the
> same image-level noise (shot noise).  

There's a reason it's called reductio ad absurdum. There is no
technology near term that I am aware of that is going to eliminate
sensor read noise; there is an inherent noise of the circuitry at the
photosite, basically thermal fluctuations which amount to a noise
power spectrum, that one is not going to eliminate (though it is not
clear that such noises have been minimized optimally in current
designs). There *are* technologies that can bypass downstream noises
though, it's just that they are not currently implemented on
production cameras. So while one can reduce or eliminate those
downstream noises, it's absurd to think that one is going to eliminate
the intrinsic kT noise of the photosite itself. The only issue is
whether the current 3-4 electron photosite read noise is a lower
bound, or whether there are improvements to be had.

For the FZ50 photosites to rival the 1D3 for per area DR, their read
noise would have to be 1.0-1.1 electrons and not the 3.3 electrons
they exhibit. But then, if that technology were available for the
small pixels, why wouldn't it be available for the large pixels,
providing them with the same per area DR that the small pixels would
enjoy?

> And from the look of things, at
> least for the near future, tiny sensors can have higher QEs, so it is
> possile that the smaller pixels can outperform at a given exposure level,
> unless the relatively poor QEs of big pixel cameras are rectified.  A lot
> depends on the "why" of the higher QE for the higher pixel densities.

My understanding is that the big-pixel champ (Nikon D3) and the small-
pixel champ (Panny FZ50) are about equal in QE. Both are gathering
about the same number of photons per unit area at raw saturation, with
the D3 at ISO 200 and the FZ50 at stated ISO 100 (which as you say are
similar in absolute sensitivity).

>
> Let us not forget that the base ISO of the FZ50 is labelled "100", but it
> is really 200 pulled a stop, in DSLR terms.

I haven't. QE and DR are distinct quantities, and it is useful to
consider both. I think the FZ50 sensor does well in QE, but not as
well as big pixel DSLR sensors (rather than cameras) in per area DR.
From: Roger N. Clark (change username to rnclark) on
David J Taylor wrote:
> Roger N. Clark (change username to rnclark) wrote:
> []
>> Once again, let's work a simple example.
>>
>> Sensor A has 100 pixels for every pixel in sensor B.
>> Both have pixels with the same read noise = 4 electrons.
>> Assume 100% fill factors and same QE.
>> Compute dynamic range for the area of pixel in sensor B.
>>
>> sensor A: X = Signal A = Signal B if we sum the signal from each
>> pixel in A (sum(100* signal in one pixel).
>>
>> read noise: sensor A = 4*sqrt(100) = 40 sensor B= 4 electrons.
>>
>> Dynamic range, DR: Sensor A DR= X/40, Sensor B: X/4
>>
>> The large pixel has higher DR.
> []
>> Roger
>
> .. but sensor A is delivering a much higher spatial resolution. Depending
> how the image is displayed, and how the eye/brain interprets the signal
> and the noise, it is not impossible that the perceived image from the
> higher resolution sensor will be preferable to that from the lower
> resolution sensor ....

Gee David, That's what I've been saying. There is an optimum.
The above was to illustrate the effects of DR and pixel size and
John's math errors regarding his DR claims.
>
> Having said that, it strikes me that for a particular
> scene/light-level/lens/display/viewing-distance combination there will be
> an optimum sensor size, and the different sensor-size cameras we use
> simply cover a different subset of the total picture-taking conditions.

Exactly.

Roger