High ISO noise

I take a picture with high ISO. Of, course it is a little noisy. My
question is what kind of noise am I seeing? Is it random noise or something
else, or a combination of things? Zooming in on a few pixels in a dark area
I see individual pixels that are obviously wrong - too bright, incorrect
color, etc. If I took the exact same picture again would these same pixels
be off in the same way or would different pixels be incorrect this time? Are
individual pixels in the camera's sensor non-linear in low-light situations?
Is this non-linearity random or is it predicable for a given sensor?

- David Harper

David Harper wrote:
I take a picture with high ISO. Of, course it is a little noisy. My
question is what kind of noise am I seeing? Is it random noise or
something else, or a combination of things? Zooming in on a few pixels
in a dark area I see individual pixels that are obviously wrong - too
bright, incorrect color, etc. If I took the exact same picture again
would these same pixels be off in the same way or would different pixels
be incorrect this time? Are individual pixels in the camera's sensor
non-linear in low-light situations? Is this non-linearity random or is
it predicable for a given sensor?

- David Harper




Yes.

Auntie

David Harper wrote:
I take a picture with high ISO. Of, course it is a little noisy. My
question is what kind of noise am I seeing? Is it random noise or
something else, or a combination of things? Zooming in on a few pixels
in a dark area I see individual pixels that are obviously wrong - too
bright, incorrect color, etc. If I took the exact same picture again
would these same pixels be off in the same way or would different pixels
be incorrect this time? Are individual pixels in the camera's sensor
non-linear in low-light situations? Is this non-linearity random or is
it predicable for a given sensor?

Digital sensor noise is in the 'z' axis, or dynamic (signal level).
That is to say that for an image (x,y) each pixel is well and self
contained in x,y, and noise due to a high ISO setting is within that
pixel.

The variance of the noise is higher and higher with a high ISO setting
and that is what gives the appearance of noise 'speckles'.

(Film on the other hand has larger (x,y) dye 'blobs' with higher ISO as
well as the dynamic variance. This is why, generally, one gets much
better high ISO results with digital than film).


--
-- 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 & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.
-- usenet posts from gmail.com and googlemail.com are filtered out.

"David Harper" wrote in message
...

I take a picture with high ISO. Of, course it is a little noisy. My
question is what kind of noise am I seeing? Is it random noise or
something else, or a combination of things? Zooming in on a few pixels in
a dark area I see individual pixels that are obviously wrong - too bright,
incorrect color, etc. If I took the exact same picture again would these
same pixels be off in the same way or would different pixels be incorrect
this time? Are individual pixels in the camera's sensor non-linear in
low-light situations? Is this non-linearity random or is it predicable for
a given sensor?

- David Harper


The bright individual pixels sound like hot pixels.

Maybe worth having a read through he
http://www.cambridgeincolour.com/tutorials/noise.htm

Mxsmanic wrote:
Alan Browne writes:

(Film on the other hand has larger (x,y) dye 'blobs' with higher ISO
as well as the dynamic variance. This is why, generally, one gets
much better high ISO results with digital than film).

My digital results at high ISO are no better than those of film.

My ISO 1600 results with a DSLR are much better than those of ~ISO 400
film.

David

David J Taylor wrote:
Mxsmanic wrote:
Alan Browne writes:

(Film on the other hand has larger (x,y) dye 'blobs' with higher ISO
as well as the dynamic variance. This is why, generally, one gets
much better high ISO results with digital than film).
My digital results at high ISO are no better than those of film.

Mxmanic is back! (I can't see your OP - Gmail I guess - filtered out).

So Mxmanic, please post comparison images to prove the above and specify
in clear detail the cameras, lenses, film, sensor settings, etc.

I was at a friends house last night and he was showing me some ISO 2500
(Nikon D3) shots printed at about 18 x 14" that showed no grain at a
normal* viewing distance and some grain for the pix-peeps. At that, the
shot was cropped somewhat.

*normal viewing distance being about 1 - 1.5 x the diagonal of the image.

--
-- 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 & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.
-- usenet posts from gmail.com and googlemail.com are filtered out.

Mxsmanic wrote:
David J Taylor writes:

My ISO 1600 results with a DSLR are much better than those of ~ISO 400
film.

Sure they are.

I believe David J

--
john mcwilliams

Mxsmanic wrote:
David J Taylor writes:

My ISO 1600 results with a DSLR are much better than those of ~ISO
400 film.

Sure they are.

Yes, they are - here's my example, straight out of the camera:

http://www.satsignal.eu/2008-10-04-1432-04.jpg

David

John McWilliams wrote:
Mxsmanic wrote:
David J Taylor writes:

My ISO 1600 results with a DSLR are much better than those of ~ISO
400 film.

Sure they are.

I believe David J

I'm all for Mxmanic posting his evidence...


--
-- 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 & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.
-- usenet posts from gmail.com and googlemail.com are filtered out.

David J Taylor wrote:
Mxsmanic wrote:
David J Taylor writes:

My ISO 1600 results with a DSLR are much better than those of ~ISO
400 film.
Sure they are.

Yes, they are - here's my example, straight out of the camera:

http://www.satsignal.eu/2008-10-04-1432-04.jpg

That has an undersaturated (overexposed) look to me.

Did you use a tripod? If so, then why not ISO 100 or 200?

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 & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.
-- usenet posts from gmail.com and googlemail.com are filtered out.