How does ISO setting work?

David J Taylor wrote:
David J. Littleboy wrote
John McWilliams wrote
Ray Fischer wrote:
John Sheehy wrote:
Ray Fischer wrote
NameHere wrote:

It doesn't increase noise per se, it only amplifies it
What a moron you are. Increasing noise doesn't increase noise?!?
The higher ISO setting per se doesn't increase noise, except on
some P&S cameras, and there, only slightly.

Yes it does.

It's the lower exposure, due to the metering for the higher ISO in
auto-exposure modes, which increases noise, relative to signal.

Inane quibbling.

Ray's confused, now attacking any one at all.

But Ray's right here. Sure, if you don't mind throwing away two stops
of highlights, ISO 400 will have lower noise. But that's a complete
snore since you can't do photography with two less stops of
highlights. So it really is exactly and only inane quibbling.

Both Ray and John Sheehy are right.

- at a given brightness [i.e. count] level in the output image, if the
ISO is increased, less exposure is needed to reach that level, and less
exposure means a lower signal-to-noise ratio.

- with a given input light level and exposure [i.e. number of photons],
increasing the ISO does not [nominally] change the signal-to-noise
ratio, but does alter the out brightness [count].

Increasing ISO for the purpose of shortening hand-holding shutter speed
is usually detrimental unless there are not highlights to be saved, and
you purposely overexpose, then dial down in post-processing. That last
approach improves things as long as you don't care about highlights.

This suggests a 2-shot HDR approach where one is overexposed with high
ISO and one is low ISO, metered to save all highlights. Apply a little
shake adjustment to match with a small crop and do it all in camera
(with 2 raw files for the nitpickers).

awaiting royalty checks from all the big camera-makers
with due share to John S.

....


...


..

Get on it Keeoit! chdk hacking sounds fun, and it probably will be
routine some day to have a number of apps running on your camera.

Neil Harrington wrote:
Most people prefer to use the lowest ISO practicable, for best image quality and definition.

On a tripod in low light or hand held in full noon sun.
If hand-held, when highlights are at risk of being blown.

While you can hand hold at that focal length, keep ISO low unless you
don't care about the highlights, then go ahead & boost the ISO (and
overexpose) to take advantage.

Gray duck moving across gray pond with no sky:
-boost ISO and overexpose (then dial down in post).

Alpine sunset at dusk with beautiful bright sky and clouds:
(and almost all scenes with a sky or important highlights)
-keep ISO low and use a tripod when needed.

"Paul Furman" wrote in message
...
[]
This suggests a 2-shot HDR approach where one is overexposed with high
ISO and one is low ISO, metered to save all highlights. Apply a little
shake adjustment to match with a small crop and do it all in camera
(with 2 raw files for the nitpickers).

awaiting royalty checks from all the big camera-makers
with due share to John S.

Something like that has already been suggested a year or two back, IIRC.
Was it, perhaps, Microsoft?

Cheers,
David

In rec.photo.digital Paul Furman wrote:
David J Taylor wrote:
David J. Littleboy wrote
John McWilliams wrote
Ray Fischer wrote:
John Sheehy wrote:
Ray Fischer wrote
NameHere wrote:

It doesn't increase noise per se, it only amplifies it
What a moron you are. Increasing noise doesn't increase noise?!?
The higher ISO setting per se doesn't increase noise, except on
some P&S cameras, and there, only slightly.

Yes it does.

It's the lower exposure, due to the metering for the higher ISO in
auto-exposure modes, which increases noise, relative to signal.

Inane quibbling.

Ray's confused, now attacking any one at all.

But Ray's right here. Sure, if you don't mind throwing away two stops
of highlights, ISO 400 will have lower noise. But that's a complete
snore since you can't do photography with two less stops of
highlights. So it really is exactly and only inane quibbling.

Both Ray and John Sheehy are right.

- at a given brightness [i.e. count] level in the output image, if the
ISO is increased, less exposure is needed to reach that level, and less
exposure means a lower signal-to-noise ratio.

- with a given input light level and exposure [i.e. number of photons],
increasing the ISO does not [nominally] change the signal-to-noise
ratio, but does alter the out brightness [count].

Increasing ISO for the purpose of shortening hand-holding shutter speed
is usually detrimental unless there are not highlights to be saved, and
you purposely overexpose, then dial down in post-processing. That last
approach improves things as long as you don't care about highlights.

This suggests a 2-shot HDR approach where one is overexposed with high
ISO and one is low ISO, metered to save all highlights. Apply a little
shake adjustment to match with a small crop and do it all in camera
(with 2 raw files for the nitpickers).

awaiting royalty checks from all the big camera-makers
with due share to John S.

Too late -- the Sony A550 already does that :-)

--
Chris Malcolm

On 10-03-08 22:01 , Paul Furman wrote:
Neil Harrington wrote:
Most people prefer to use the lowest ISO practicable, for best image
quality and definition.

On a tripod in low light or hand held in full noon sun.
If hand-held, when highlights are at risk of being blown.

While you can hand hold at that focal length, keep ISO low unless you
don't care about the highlights, then go ahead & boost the ISO (and
overexpose) to take advantage.

Gray duck moving across gray pond with no sky:
-boost ISO and overexpose (then dial down in post).

Alpine sunset at dusk with beautiful bright sky and clouds:
(and almost all scenes with a sky or important highlights)
-keep ISO low and use a tripod when needed.


I'm beginning to think the new press aphorism will be:

"ISO 800 and be there."


--
gmail originated posts are filtered due to spam.

John A. wrote:
Chris Malcolmwrote:
Paul Furman wrote:

Increasing ISO for the purpose of shortening hand-holding shutter speed
is usually detrimental unless there are not highlights to be saved, and
you purposely overexpose, then dial down in post-processing. That last
approach improves things as long as you don't care about highlights.

This suggests a 2-shot HDR approach where one is overexposed with high
ISO and one is low ISO, metered to save all highlights. Apply a little
shake adjustment to match with a small crop and do it all in camera
(with 2 raw files for the nitpickers).

awaiting royalty checks from all the big camera-makers
with due share to John S.

Too late -- the Sony A550 already does that :-)

Pentax K7 as well.

Closest Nikon has is to underexpose then lift the shadows.

DanP wrote in
:

You don't fool anyone.

Am I supposed to guess what that means?

Paul Furman wrote in -
september.org:

Closest Nikon has is to underexpose then lift the shadows.

Well, Nikon has a number of cameras with very "liftable" low-ISO shadows.
Canon is plagued with excessive shadow banding at low ISOs. The 7D has a
lot of banding at low ISOs, but much of it is fixed pattern (and some
apparently caused by poor firmware correction), and could have conceivable
be calibrated out. I can get a decent small web-image from my 7D at ISO
100 under-exposed 8 stops, after subtracting a stack of blackframes.

"Neil Harrington" wrote in
:

Image noise increases at high ISO. At some point this may make the
picture unacceptably grainy, depending on what you consider
acceptable. Most people prefer to use the lowest ISO practicable, for
best image quality and definition. There may be "artistic" reasons to
do otherwise, of course.

Perhaps, but you can add much better-looking noise in software than the
ugly read noise artifacts - unless, of course, you *want* ugly readout
artifacts, in which case, you will do better by under-exposing base ISO on
many DSLRs.


Definitely, ISO 3200 would produce more noise than ISO 400.

It's more like an actual exposure index of 3200 results in 1/8 the
exposure, with a higher resulting SNR. The electronics at ISO 3200 do not
add any more noise than 400 in DSLRs, relative to signal. This may sound
pedantic, but your choice of the word "produce" actually creates an
incorrect statement. The camera doesn't produce more noise at higher ISOs
(except for some P&S cameras); the lower absolute exposure (lesser photon
collection) produces the lower SNR.

Paul Furman wrote in -
september.org:

Alpine sunset at dusk with beautiful bright sky and clouds:
(and almost all scenes with a sky or important highlights)
-keep ISO low and use a tripod when needed.

As computers/storage/firmware get faster, we could be shooting 16 ISO 1600
shots in rapid succession for an aligned ISO 100 composite, for a less read
noise, and less camera shake blur, than "normal" ISO 100.