Source of Noise

[mrod]

Hi all-

So, here's a question I have after a recent shoot:

- What are various causes of noise in a given image?

I know a high ISO will do it...what else?

Example:

Here's a screen shot of part of a road sign I shot the other night.

http://www.pixentral.com/hosted/1iUfvrCdVkqv6hyWv5oJJkcgz6KW_thumb.jpg (http://www.pixentral.com/show.php?picture=1iUfvrCdVkqv6hyWv5oJJkcgz6KW)

ISO 100, f/5.6, 1/500 sec.

I zoomed in to 300% so you could better see the noise in the yellow of the sign, but it's definitely visible at 100%. And it only turned up on the right side of the sign. The left and middle areas were nearly noise/artifact-free.

So, any theories on the source of the noise? Could a lens do it? I shot this on a borrowed Nikkor 50-200 VR, so it wasn't my usual lens (in hindsight, I should have done a shot with my regular lens, too...).

I also wouldn't be shocked at all to discover the culprit is User Error...:rolleyes:

Thanks,
Mike

[CalamityJanet]

Hi Mike,

What I'm seeing doesn't look like the noise I usually see in my images. Could it be that the sign was painted with that reflective paint so it will be more visible at night? That paint looks kind of grainy when you see it up close. And depending on the source of light in your photo it may be more visible on one side of the sign. Just a thought...

I've read that in digital cameras a long exposure time causes the sensor to heat up and that can cause noise, but your 1/500 would seem to eliminate that as a cause.

[rkmart]

This link might help. :):)

http://www.photoxels.com/tutorial_noise.html

[Edmund]

Mike, I am no expert so I went to the best source for these technical questions at the "Luminous Landscape"
http://luminous-landscape.com/tutorials/noise.shtml
It is quite Technical but does discuss that there are many factors that can cause sensor noise besides ISO. Good read.
Eddie:)

[Ellen]

Mike - I just have a p&s but the paint in reflective signs does do odd things in my photos, it's different from regular noise.

[Not4wood]

What I find interesting, is not only is this reflective sign causing some maybe aberation but you didn't say what camera you used for the shot.

Depending on what camera even on my D80 I wont get any kind of noise at ISO 100 and again what kind of sensor you have might have caused this grain. Doesn't look like noise to me on my calibrated monitor.

[mrod]

Great info and insights, everyone. Thanks. I'll check out those articles, Robert and Eddie.

And you all may be right--it might not be noise. I didn't consider the reflective qualities of the paint. Maybe the angle I was shooting at caused part of the sign to look the way it did.

Mark, I also shoot with a D80, so we're comparing apples to apples here.

Mike

[lexcell]

Mike,
everyone has jumped in and given you some excellent things to think about plus some links to follow.
As suggested, it is likely not noise in this particular image.
Your exposure should not have generated noise...you weren't shooting at a high ISO, in low light or underexposing your image which are the three biggest causes of noise.
I would try a similar shot of a different subject in similar light and at a similar exposure to see if you still get noise.

[Rooeey]

http://www.luminous-landscape.com/tutorials/expose-right.shtml>

I have tried it and it seems to help but i think it is most benneficial when shooting RAW...