What Creates Noise/Grain At Higher ISO Speeds?

What is the actual reason why photos shot at higher ISO speeds create
noise/grain?

In film, I can understand that to produce films which is more sensitive to
light, the chemistry may be different, but why is this evident with digital?

If you look here, noise is very evident in this digital shot, but I am
puzzled why it occurs:
http://www.pbase.com/jps_photo/image/36330285/original

In message ,
"Matt" wrote:

What is the actual reason why photos shot at higher ISO speeds create
noise/grain?

In film, I can understand that to produce films which is more sensitive to
light, the chemistry may be different, but why is this evident with digital?

If you look here, noise is very evident in this digital shot, but I am
puzzled why it occurs:
http://www.pbase.com/jps_photo/image/36330285/original

Do you realize what you are looking at there? (Most of) the image was
highly sharpened with no noise-reduction, and this is at ISO 1600. You
are looking at what would be a 40 inch by 27 inch full image, if your
monitor were big enough to display it; that's over 3 feet wide. Also,
the optics are at the limits of their resolution, so there is no
high-contrast image detail to compete with the noise. The noise got
sharpened more than the detail. Look at the left and bottom edges;
there is no sharpening there.
--


John P Sheehy

The point of this example was not to say this was a poor photo, just to give
an example of noise. It was chose randomly only as an example of noise.

If I knew this would upset people, I would not have included the link. I
included the link purely as an example.

I hope I have not offended anyone.




wrote in message
...

Do you realize what you are looking at there? (Most of) the image was
highly sharpened with no noise-reduction, and this is at ISO 1600. You
are looking at what would be a 40 inch by 27 inch full image, if your
monitor were big enough to display it; that's over 3 feet wide. Also,
the optics are at the limits of their resolution, so there is no
high-contrast image detail to compete with the noise. The noise got
sharpened more than the detail. Look at the left and bottom edges;
there is no sharpening there.
--


John P Sheehy

Amplification of the signal, they also amplify the noise thats present , as
well as the low level signal at higher ISOs.

"Matt" wrote in message
...
What is the actual reason why photos shot at higher ISO speeds create
noise/grain?

In film, I can understand that to produce films which is more sensitive to
light, the chemistry may be different, but why is this evident with
digital?

If you look here, noise is very evident in this digital shot, but I am
puzzled why it occurs:
http://www.pbase.com/jps_photo/image/36330285/original

Amplification of the signal, they also amplify the noise thats present , as
well as the low level signal at higher ISOs.

"Matt" wrote in message
...
What is the actual reason why photos shot at higher ISO speeds create
noise/grain?

In film, I can understand that to produce films which is more sensitive to
light, the chemistry may be different, but why is this evident with
digital?

If you look here, noise is very evident in this digital shot, but I am
puzzled why it occurs:
http://www.pbase.com/jps_photo/image/36330285/original

Many of the explanations for noise in electronic sensors are based on the
technical limits of the early digital technology we are still using. As such
they are misleading.

One of the misconceptions is that smaller digital sensors can never yield
the lower noise now seen in larger sensors. The fact is that noise levels
will decrease in all digital sensors as more experience is gained in the
design and manufacture of these devices. So will the dynamic range of light
values the sensors are able to capture. Claims to this effect are already
being made for the newest Canon and Fuji dSLRs.

Manufacturer's claims, like those of politicians, occasionally coincide with
reality.

The most important limiting factor in reducing the size and performance
(regardless of sensor size) of high resolution digital sensors has nothing
to do with sensor technology but has to do with the inherent properties of
light, reflection (above and within the sensor), diffaction and the
inescapable problems of bringing all color light rays into focus at the same
plane. The sort of optical noise that is caused by the intereacting
properties of light, lenses and the flat plane of digital sensors
(regardless of sensor size) is already underappreciated in evaluating the
performances of current digital cameras. Because of these effects the
designs of lenses for high end digital cameras are going in directions that
film cameras did not require.

Software may be part of the solution. Programs already exist for
post-exposure tweaking of vignetting, barrel and pincusion distortion but
they require manual tweaking. Who knows what the future will bring? Olympus
has publicly stated it is moving toward building this sort of post-exposure
processing into its dSLR line.

Matt wrote:

What is the actual reason why photos shot at higher ISO speeds create
noise/grain?

In film, I can understand that to produce films which is more sensitive to
light, the chemistry may be different, but why is this evident with digital?

If you look here, noise is very evident in this digital shot, but I am
puzzled why it occurs:
http://www.pbase.com/jps_photo/image/36330285/original

Film suffers larger physical grain (dye clouds) in the plane of the film (call
it x,y) as the ISO goes up. Faster speed = larger 'grain' or dye clouds. This
results in the grain that you see. It's not really that cut and dry, but the
end result is coarseness in the negative image that we call "grainy".

In digital, the x,y is constant regardless of the sensitivity... the grain size
will always be the same for a given sensor. However, the noise level will be
different from pixel to pixel, and this difference is amplified by the
increasing sensitivity... that is what gives the noisy 'grainy' look on high ISO
digital shots. The 'grains' remain the same size, but there is a greater
dynamic difference between them due to noise. This is more complex than that,
as each pixel that you see from most SLR's is a composite of several pixels of
different color. The noise response in, eg, red, green and blue channels is
different for each color and this further makes pixel to pixel noise differences
more apparent in the resulting end pixel.

Hope that helps.

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI gallery]: http://www.pbase.com/shootin
-- [SI rulz]: http://www.aliasimages.com/si/rulz.html
-- e-meil: there's no such thing as a FreeLunch.

Matt wrote:

What is the actual reason why photos shot at higher ISO speeds create
noise/grain?

In film, I can understand that to produce films which is more sensitive to
light, the chemistry may be different, but why is this evident with digital?

If you look here, noise is very evident in this digital shot, but I am
puzzled why it occurs:
http://www.pbase.com/jps_photo/image/36330285/original

Film suffers larger physical grain (dye clouds) in the plane of the film (call
it x,y) as the ISO goes up. Faster speed = larger 'grain' or dye clouds. This
results in the grain that you see. It's not really that cut and dry, but the
end result is coarseness in the negative image that we call "grainy".

In digital, the x,y is constant regardless of the sensitivity... the grain size
will always be the same for a given sensor. However, the noise level will be
different from pixel to pixel, and this difference is amplified by the
increasing sensitivity... that is what gives the noisy 'grainy' look on high ISO
digital shots. The 'grains' remain the same size, but there is a greater
dynamic difference between them due to noise. This is more complex than that,
as each pixel that you see from most SLR's is a composite of several pixels of
different color. The noise response in, eg, red, green and blue channels is
different for each color and this further makes pixel to pixel noise differences
more apparent in the resulting end pixel.

Hope that helps.

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI gallery]: http://www.pbase.com/shootin
-- [SI rulz]: http://www.aliasimages.com/si/rulz.html
-- e-meil: there's no such thing as a FreeLunch.

Matt wrote:

The point of this example was not to say this was a poor photo, just to give
an example of noise. It was chose randomly only as an example of noise.

See my other reply.

If I knew this would upset people, I would not have included the link. I
included the link purely as an example.

And a good thing you did.


I hope I have not offended anyone.

Nah. Don't worry about assorted crankies.

Cheers,
Alan

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI gallery]: http://www.pbase.com/shootin
-- [SI rulz]: http://www.aliasimages.com/si/rulz.html
-- e-meil: there's no such thing as a FreeLunch.

wrote:


I hope I have not offended anyone.


No one is upset or offended. I was just bringing to your attention that
this is a crop; it is less than 5% of the full image, are-wise, and
about 22% of the image in each dimension. There are woods surrounding
the carton, and a female Cardinal looking at the container, in the
original image.

I believe the gent wanted to know "why is this so?" and not have a blast over
his particular posted example.

Cheers,
Alan.


--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI gallery]: http://www.pbase.com/shootin
-- [SI rulz]: http://www.aliasimages.com/si/rulz.html
-- e-meil: there's no such thing as a FreeLunch.