From: John Sheehy on
Scott W <biphoto(a)hotmail.com> wrote in
news:381a062a-105d-4b40-92e7-08c023b59bf2(a)r66g2000hsg.googlegroups.com:

> John, you should really redo the test with the ISO set higher on the
> 400D, clearly you can also set it higher on the FZ50 as well.

No, I shouldn't, because that would be a different issue altogether.
I've already said, many times, that the highest ISOs in some models of
DSLRs have area-based read noise as good or slightly better than clusters
of current P&S pixels in aggregate. It's a given that the 400D would
give less noise if it were set to ISO 1600.

This test is *NOT* about shooting at high ISOs. It is about the shadows
(the weakest areas) at base or low ISOs.

> I know in tests i have done shooting at higher iso, when using the
> same shutter speed and f/stop, reduces the noise by a lot, you can see
> the test images here
> http://www.pbase.com/konascott/image/71375911
> All 5 images were taken at f/11 and 1/30 sec.

I was one of the first people to ever notice this, and I popularized it
here and elsewhere a few years back. That is old hat. What I am
demonstrating here is a more advanced topic, one that causes a lot of
cognitive dissonance in people with pixel-centric imaging philosophies.
People actually believe that the noise of a pixel is the noise of an
image; that the DR of a pixel is the DR of an image.

> It would also be interesting to see the image from the FZ50 reduced in
> size to match the 400D, as well as the other way around.

What would that mean? I supplied 100% crops from both cameras, and each
scaled to the other.

--

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John P Sheehy <JPS(a)no.komm>
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From: Roger N. Clark (change username to rnclark) on
John Sheehy wrote:
> Scott W <biphoto(a)hotmail.com> wrote in
> news:381a062a-105d-4b40-92e7-08c023b59bf2(a)r66g2000hsg.googlegroups.com:
>
>> John, you should really redo the test with the ISO set higher on the
>> 400D, clearly you can also set it higher on the FZ50 as well.
>
> No, I shouldn't, because that would be a different issue altogether.
> I've already said, many times, that the highest ISOs in some models of
> DSLRs have area-based read noise as good or slightly better than clusters
> of current P&S pixels in aggregate. It's a given that the 400D would
> give less noise if it were set to ISO 1600.
>
> This test is *NOT* about shooting at high ISOs. It is about the shadows
> (the weakest areas) at base or low ISOs.

If that is your test, you biased the result in the FZ50 images by a factor
of more than 20. The FZ50 has a max signal at ISO 100 of about 2000 electrons
or so and the 400D over 40,000. So the FZ50 saturates some 4.3 stops
lower than the 400D. So if you equalize the high end, the 400D reaches
some 4.3 stops lower.

All this comes down to the electronic gains in the two cameras are different
in your test. Unless you make those close to equal, your test is
biased.

Roger
From: JufĂ­ on

"John Sheehy" <JPS(a)no.komm> wrote in message
news:Xns9ADDEE88478A7jpsnokomm(a)199.45.49.11...
> "Jufi" <bowser(a)work.com> wrote in
> news:e3lfk.31$X6.8(a)bos-service2b.ext.ray.com:
>
>> Uh, OK. So why not compare cameras with the same size sensors but
>> different numbers of pixels?
>
> Do you have any idea how hard it is to find RAW data from two different
> cameras of the exact same scene, with the exact same lighting, and the
> exact same perspective point and exposure, and same real focal length? I
> can not depend on other people; other people do not do things right.
> They will vary something; probably a few things. I must work with what I
> have. Besides, there is *VERY* little range in pixel pitch amongst
> sensors of the same size, especially of the same technology era. The
> results could be written off to small differences in support electronics,
> quaantum efficiency, etc. You really need to compare *grossly* different
> pixel sizes (preferably of the same era) to get the most meaningful
> insight into differences of pixel pitch.

Since you can't acquire cameras with sensors of the same physical size that
produce raw data, and can only compare grossly different cameras and
sensors, what's the point of this excercise? Even if it did prove something,
what good is the info is you can't possibly make use of it?

From: Steve on

On Thu, 17 Jul 2008 03:36:20 GMT, John Sheehy <JPS(a)no.komm> wrote:

>John O'Flaherty <quiasmox(a)yeeha.com> wrote in
>news:g5bs7490188ng5i849tmko3ma6aat0sh19(a)4ax.com:
>
>>>Of course, such a test would give a result already expected by almost
>>>anyone who knows anything at all about digital imaging, but would tell
>>>us absolutely nothing about the effects of pixel *density*; only about
>>>sensor size.
>
>> That clarifies it. In your post, you said that "the bigger pixels of
>> the DSLR are inferior compared to the higher pixel density of the
>> small sensor camera"; apples and orange juice.
>
>What I am demonstrating needs to be demonstrated. There is too much
>nonsense out there circulating as fact, suggesting that the more pixels
>you "stuff" into a given sensor size, the noisier the images get, the
>less DR they have, etc, etc. This clearly shows that this is not true,
>that pixels covering less of the focal plane each can currently do much
>better than big pixels, at representing the area that they are
>responsible for.

You may think your test shows that small pixels covering less of the
focal plane each can do more than big pixels at representing the area
they are responsible for. But because you are trying to account for
the difference in sensor size between the 400D and the FZ50 by blowing
up the 400D image so much more than the FZ50, your test does *not*
show anything to disprove the notion that stuffing more pixels into a
"given sensor size" (quote from you above) causes the images to get
noiser and DR to get lower.

In order to prove that with different sensor sizes and have any kind
of meaningful real-world results, you must allow both sensors to
capture the same entire image and then look at crops from both where
the relative "blow up" of each only depends on the megapixels of each.
So if you're comparing two 10MP sensors of different sizes, you could
look at 100% crops from both and see the same image area. But if one
is a 10MP sensor and the other is a 12MP sensor, you could look at a
100% crop of the 12MP sensor but would have to blow up the 10MP sensor
to 120%. Or make the 10MP 100% but the 12MP could be compared at only
an 83% enlargement.

Or, if you really wanted to try and prove that stuffing more pixels
into a "given sensor size" does not cause images to get noiser and
lose DR, then you have to really do what you're trying to prove. That
is, compare 2 sensors of the same size but different pixel densities.
At the high end, maybe a FF D3 at 12MP to a FF 1DsMkIII at 21MP. Or
if you like comparing pocket cameras, a lot of them have the same
sensor sizes but different pixel densities. Just find 2 diffenent
ones that can output raw.

>
>This test, however, is not about DR, per se, as the 400D still has some
>more headroom than the FZ50 here. It is more about absolute sensitivity
>in this case, although the usable DR should still be better with the
>smaller pixels.

You haven't proved that and the entire rest of the world has disproved
that.

Steve
From: Steve on

On Thu, 17 Jul 2008 03:52:16 GMT, John Sheehy <JPS(a)no.komm> wrote:

>rfischer(a)sonic.net (Ray Fischer) wrote in news:487d881a$0$17222
>$742ec2ed(a)news.sonic.net:
>
>> John P Sheehy <jps(a)no.kom> wrote:
>>>I've made a direct comparison of RAW data per unit of area in the deep
>
>> "per unit area"
>
>> In other words, if you know what results you want to get then you can
>> adjust your measurement to get those results.
>
>I made a direct comparison of combined read and shot noise relative to
>absolute signal, and resolution, of two different pixel densities capturing
>the same area of a focal plane from the same scene with the same focal
>length and li9ght intensity.

That may be what you did, but it doesn't prove what you're trying to
prove, i.e., stuffing more pixels into a given sensor size doesn't
degrade noise or DR. In doing what you did above, the sensor from the
400D would be capturing an image that is overall several times the
area of the FZ50. No one in their right mind would consider that a
fair comparison of different sensor sizes when what you're trying to
prove is whether stuffing in more pixels does not degrade noise and DR
for a "given sensor size."

Steve