Dummy question about CCDs and noise

One must not make a blanket statement on this. It is one of those "all
else being equal..." things. The area density (actually, the area of
each pixel) is only one factor in the total noise of a detector. And,
we must be careful to differentiate original detector noise from the
final 'noise' in the output file. Post processing CAN reduce noise,
but it depends on the algorithms used. I suspect the difference in
the two cases below would not show a dramatic difference in noise
either way.

The final noise in an image is a result of inherent detector noise,
preamp noise, quantization noise, processing algorithm noise, and the
phase of the moon.


"J.S.Pitanga" wrote in message news:opsgze2lm0q1cbtl@jsp...
Hi there,

It is known that a higher amount of pixels per area of CCD tends to
produce a higher amount of noise. Thus, a 3mp 1/2.5" CCD would produce
less noise than a 4mp 1/2.5" CCD.

My question is whether a camera with a 4mp 1/2.5" CCD but set to a
resolution 3mp produces an amount of noise typical of its 4mp CCD or a
lower amount of noise, such as that of a 3mp 1/2.5" CCD?

Thanks in advance for any answers,

J.S.Pitanga

Kibo informs me that "J.S.Pitanga" stated
that:

Hi there,

It is known that a higher amount of pixels per area of CCD tends to
produce a higher amount of noise. Thus, a 3mp 1/2.5" CCD would produce
less noise than a 4mp 1/2.5" CCD.

In general, yes, that's correct, & a useful rule of thumb. But you need
to remember that it relates only to the theoretical limits of a silicon
photosensor only. There are many other factors involved besides the
photosite size that also affect noise levels, such as ambient heat, the
quality (ie $$$, skill & creativity) that went into the design of the
sense-amps, conditioning circuitry, A2D converter & other support
electronics. Then there's the digital processing by the cameras onboard
computer, which typically includes software noise-reduction & other
enhancements.
(These sorts of factors are why a Brand 'X' 4MP, 1/2.5" sensor camera
might have very different noise levels to a Brand 'Y' camera that has a
sensor of the same size & resolution, & why, (for a recent example),
Canon were able to make the EOS 20D, 8MP DSLR *less* noisy than the 10D,
despite having about 25% more pixels on the same size sensor.)

My question is whether a camera with a 4mp 1/2.5" CCD but set to a
resolution 3mp produces an amount of noise typical of its 4mp CCD or a
lower amount of noise, such as that of a 3mp 1/2.5" CCD?

Your question is not even slightly dumb. It's actually very perceptive.


In theory, summing data from multiple photosites should indeed reduce
noise somewhat, much as it would if the sensor had the smaller number of
photosites, with the equivalently larger area. And most of the time, it
works in practice, & you'll find (unless your camera is poorly
designed), that high-ISO images will look less noisy if taken at smaller
resolutions.

So, the obvious interpretation of this relationship would seem to imply
that if you're finding noise to be a problem in your photos (eg;
available light shooting at ISO 400+ on a digicam), & want cleaner
photos, it'd be helpful to shoot at a lower resolution than that of the
sensor itself.
*However* - you don't need to do that, because the maths that governs
the noise vs photosite-size tradeoff on the sensor also applies to /any
stage/ between the light hitting the photosite & you printing the
resulting image on your inkjet or at your local lab. This means that,
all else being equal, you can also reduce noise in your images by simply
reducing the resolution of your image after you've taken it. This means
that you lose nothing (except disk space), by shooting at the native
resolution of your camera, & simply reducing the size of the image in
Photoshop (or any other program that scales with a high-quality
algorithm).
You can easily demonstrate this for yourself by taking a photo at your
cameras highest resolution & ISO setting, then again at a much smaller
size (eg; 50%), then resampling the large image in Photoshop down to the
exact same resolution. You will most likely find that, (again, all else
being equal, etc), both images will have similar amounts of noise.

So, to rephrase your original question: Is a 3MP image from a 4MP
sensor going to be less noisy than an otherwise identical 4MP image from
the same sensor? - The answer is most likely 'yes', but not by a whole
lot, due to the final image being nearly as big as the sensor. Also, it
is unlikely to give you any advantage (in terms of noise levels), over
just shooting at 4MP & resizing to 3MP on your computer.

Thanks in advance for any answers,

My pleasure. I hope you found my comments informative.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

Kibo informs me that "J.S.Pitanga" stated
that:

Hi there,

It is known that a higher amount of pixels per area of CCD tends to
produce a higher amount of noise. Thus, a 3mp 1/2.5" CCD would produce
less noise than a 4mp 1/2.5" CCD.

In general, yes, that's correct, & a useful rule of thumb. But you need
to remember that it relates only to the theoretical limits of a silicon
photosensor only. There are many other factors involved besides the
photosite size that also affect noise levels, such as ambient heat, the
quality (ie $$$, skill & creativity) that went into the design of the
sense-amps, conditioning circuitry, A2D converter & other support
electronics. Then there's the digital processing by the cameras onboard
computer, which typically includes software noise-reduction & other
enhancements.
(These sorts of factors are why a Brand 'X' 4MP, 1/2.5" sensor camera
might have very different noise levels to a Brand 'Y' camera that has a
sensor of the same size & resolution, & why, (for a recent example),
Canon were able to make the EOS 20D, 8MP DSLR *less* noisy than the 10D,
despite having about 25% more pixels on the same size sensor.)

My question is whether a camera with a 4mp 1/2.5" CCD but set to a
resolution 3mp produces an amount of noise typical of its 4mp CCD or a
lower amount of noise, such as that of a 3mp 1/2.5" CCD?

Your question is not even slightly dumb. It's actually very perceptive.


In theory, summing data from multiple photosites should indeed reduce
noise somewhat, much as it would if the sensor had the smaller number of
photosites, with the equivalently larger area. And most of the time, it
works in practice, & you'll find (unless your camera is poorly
designed), that high-ISO images will look less noisy if taken at smaller
resolutions.

So, the obvious interpretation of this relationship would seem to imply
that if you're finding noise to be a problem in your photos (eg;
available light shooting at ISO 400+ on a digicam), & want cleaner
photos, it'd be helpful to shoot at a lower resolution than that of the
sensor itself.
*However* - you don't need to do that, because the maths that governs
the noise vs photosite-size tradeoff on the sensor also applies to /any
stage/ between the light hitting the photosite & you printing the
resulting image on your inkjet or at your local lab. This means that,
all else being equal, you can also reduce noise in your images by simply
reducing the resolution of your image after you've taken it. This means
that you lose nothing (except disk space), by shooting at the native
resolution of your camera, & simply reducing the size of the image in
Photoshop (or any other program that scales with a high-quality
algorithm).
You can easily demonstrate this for yourself by taking a photo at your
cameras highest resolution & ISO setting, then again at a much smaller
size (eg; 50%), then resampling the large image in Photoshop down to the
exact same resolution. You will most likely find that, (again, all else
being equal, etc), both images will have similar amounts of noise.

So, to rephrase your original question: Is a 3MP image from a 4MP
sensor going to be less noisy than an otherwise identical 4MP image from
the same sensor? - The answer is most likely 'yes', but not by a whole
lot, due to the final image being nearly as big as the sensor. Also, it
is unlikely to give you any advantage (in terms of noise levels), over
just shooting at 4MP & resizing to 3MP on your computer.

Thanks in advance for any answers,

My pleasure. I hope you found my comments informative.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

"J.S.Pitanga" wrote in message news:opsgze2lm0q1cbtl@jsp...
Hi there,

It is known that a higher amount of pixels per area of CCD tends to
produce a higher amount of noise. Thus, a 3mp 1/2.5" CCD would produce
less noise than a 4mp 1/2.5" CCD.

My question is whether a camera with a 4mp 1/2.5" CCD but set to a
resolution 3mp produces an amount of noise typical of its 4mp CCD or a
lower amount of noise, such as that of a 3mp 1/2.5" CCD?

Thanks in advance for any answers,

J.S.Pitanga

Downsizing reduces noise, so it should be closer to tha from a 3mp CCD
than a 4mp CCD, all things being equal.

-Tripurari

"J.S.Pitanga" wrote in message news:opsgze2lm0q1cbtl@jsp...
Hi there,

It is known that a higher amount of pixels per area of CCD tends to
produce a higher amount of noise. Thus, a 3mp 1/2.5" CCD would produce
less noise than a 4mp 1/2.5" CCD.

My question is whether a camera with a 4mp 1/2.5" CCD but set to a
resolution 3mp produces an amount of noise typical of its 4mp CCD or a
lower amount of noise, such as that of a 3mp 1/2.5" CCD?

Thanks in advance for any answers,

J.S.Pitanga

Downsizing reduces noise, so it should be closer to tha from a 3mp CCD
than a 4mp CCD, all things being equal.

-Tripurari

Bob Williams wrote in message ...
J.S.Pitanga wrote:
Hi there,

It is known that a higher amount of pixels per area of CCD tends to
produce a higher amount of noise. Thus, a 3mp 1/2.5" CCD would produce
less noise than a 4mp 1/2.5" CCD.

My question is whether a camera with a 4mp 1/2.5" CCD but set to a
resolution 3mp produces an amount of noise typical of its 4mp CCD or a
lower amount of noise, such as that of a 3mp 1/2.5" CCD?

Thanks in advance for any answers,

J.S.Pitanga

The noise will be the same at 4 or 3 MP.
Your camera CAPTURES all 4 MP, regardless of your setting.
After capturing, the camera will resample the image downward to 3MP and
then SAVE the resampled image on your memory card.
Bob Williams

The camera does capture at 4mp, but downsizing reduces noise by
averaging pixel values.

-Tripurari

Bob Williams wrote in message ...
J.S.Pitanga wrote:
Hi there,

It is known that a higher amount of pixels per area of CCD tends to
produce a higher amount of noise. Thus, a 3mp 1/2.5" CCD would produce
less noise than a 4mp 1/2.5" CCD.

My question is whether a camera with a 4mp 1/2.5" CCD but set to a
resolution 3mp produces an amount of noise typical of its 4mp CCD or a
lower amount of noise, such as that of a 3mp 1/2.5" CCD?

Thanks in advance for any answers,

J.S.Pitanga

The noise will be the same at 4 or 3 MP.
Your camera CAPTURES all 4 MP, regardless of your setting.
After capturing, the camera will resample the image downward to 3MP and
then SAVE the resampled image on your memory card.
Bob Williams

The camera does capture at 4mp, but downsizing reduces noise by
averaging pixel values.

-Tripurari

Tripurari Singh wrote:
Bob Williams wrote in message ...

J.S.Pitanga wrote:

Hi there,

It is known that a higher amount of pixels per area of CCD tends to
produce a higher amount of noise. Thus, a 3mp 1/2.5" CCD would produce
less noise than a 4mp 1/2.5" CCD.

My question is whether a camera with a 4mp 1/2.5" CCD but set to a
resolution 3mp produces an amount of noise typical of its 4mp CCD or a
lower amount of noise, such as that of a 3mp 1/2.5" CCD?

Thanks in advance for any answers,

J.S.Pitanga

The noise will be the same at 4 or 3 MP.
Your camera CAPTURES all 4 MP, regardless of your setting.
After capturing, the camera will resample the image downward to 3MP and
then SAVE the resampled image on your memory card.
Bob Williams


The camera does capture at 4mp, but downsizing reduces noise by
averaging pixel values.

-Tripurari

But it also degrades the image.
There is NO WAY to increase the signal-to-noise ratio of an image.
If there was, you could continue using it until the image was sharp as a
tack and noise free.
Like a free lunch......it never works out that way.
Bob Williams

Tripurari Singh wrote:
Bob Williams wrote in message ...

J.S.Pitanga wrote:

Hi there,

It is known that a higher amount of pixels per area of CCD tends to
produce a higher amount of noise. Thus, a 3mp 1/2.5" CCD would produce
less noise than a 4mp 1/2.5" CCD.

My question is whether a camera with a 4mp 1/2.5" CCD but set to a
resolution 3mp produces an amount of noise typical of its 4mp CCD or a
lower amount of noise, such as that of a 3mp 1/2.5" CCD?

Thanks in advance for any answers,

J.S.Pitanga

The noise will be the same at 4 or 3 MP.
Your camera CAPTURES all 4 MP, regardless of your setting.
After capturing, the camera will resample the image downward to 3MP and
then SAVE the resampled image on your memory card.
Bob Williams


The camera does capture at 4mp, but downsizing reduces noise by
averaging pixel values.

-Tripurari

But it also degrades the image.
There is NO WAY to increase the signal-to-noise ratio of an image.
If there was, you could continue using it until the image was sharp as a
tack and noise free.
Like a free lunch......it never works out that way.
Bob Williams

Bob Williams wrote:


Tripurari Singh wrote:

Bob Williams wrote in message
...

J.S.Pitanga wrote:

Hi there,

It is known that a higher amount of pixels per area of CCD tends to
produce a higher amount of noise. Thus, a 3mp 1/2.5" CCD would
produce less noise than a 4mp 1/2.5" CCD.

My question is whether a camera with a 4mp 1/2.5" CCD but set to a
resolution 3mp produces an amount of noise typical of its 4mp CCD or
a lower amount of noise, such as that of a 3mp 1/2.5" CCD?

Thanks in advance for any answers,

J.S.Pitanga


The noise will be the same at 4 or 3 MP.
Your camera CAPTURES all 4 MP, regardless of your setting.
After capturing, the camera will resample the image downward to 3MP
and then SAVE the resampled image on your memory card.
Bob Williams



The camera does capture at 4mp, but downsizing reduces noise by
averaging pixel values.

-Tripurari


But it also degrades the image.
There is NO WAY to increase the signal-to-noise ratio of an image.

There are many PS filters, actions, plugins and standalone apps that
decrease noise, thus increasing at least the apparent ratio.

If there was, you could continue using it until the image was sharp as a
tack and noise free.

[If there were, but there is!]: It doesn't follow that you get both
noise reduction and sharpness. Nor does any beneficial adjustment work
on a straight line or even a favorable curve. At some point the
tradeoffs become quite unacceptable.

Like a free lunch......it never works out that way.

Amen to that!

--
John McWilliams