Red noise 40d

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Archive 2008 · Red noise 40d

dslrintraining
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p.1 #1 · Red noise 40d

I shot at the Limerock Vintage festival this summer, and I noticed that at ISO 800, the pictures all looked fine with no noise except for the red cars, they had lots of noise. I was looking at other pictures I have of red cars at ISO 400, and even then there was significant noise in reds. Is this normal? Do all cameras have lots of red noise, is is too much for the sensor to handle? I was shooting with my 28-135mm. Thanks

Oct 07, 2008 at 11:21 PM

dslrintraining
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p.1 #2 · Red noise 40d

I cropped this a little bit, but not much to show the noise.

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Oct 07, 2008 at 11:53 PM

Gary Petersen
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p.1 #3 · Red noise 40d

It's a bit underexposed from where I would shoot it. That doesn't help the noise any. All three channels are noisy btw.

Oct 08, 2008 at 03:44 AM

LCollector
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p.1 #4 · Red noise 40d

OP, read this: http://www.imaging-resource.com/PRODS/E40D/E40DIMATEST.HTM

I think you got it right...red channel seems to have the highest noise according to this doc.

cut-paste:
What's very odd here though, is how much more noise energy the red channel has at low frequencies, seen in the large spike on the left-hand side of the curve. This might be an issue, but the overall noise levels are so low that the noise spike in the red channel isn't really visible at ISO 100.

Oct 08, 2008 at 03:54 AM

ejmartin
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p.1 #5 · Red noise 40d

Without seeing the raw data, there are several possible sources for the noise. One is overall underexposure, low S/N due to low signal which will make all color channels noisy as exposure compensation is applied during raw conversion -- amplifying the signal to bring it to proper exposure amplifies the noise along with it. Another issue is white balance; the red channel can be a stop or more underexposed relative to the green channel in the raw data due to the spectral content of the light illuminating the scene. White balance during raw conversion (either in the camera's jpeg engine or in a raw converter) again amplifies the red channel data to achieve perceptual white balance, and again amplifies the noise along with it.

LCollector: The spatial frequency dependence of noise in any color channel is an artifact of the raw conversion process, specifically demosaicing of the Bayer data. The spatial frequency dependence of noise in the raw data is uniform ("white noise") in the raw data, since the noise is uncorrelated from photosite to photosite (to a good approximation for read noise, and exactly for photon shot noise). The folks at IR and DPR would do well to understand what their tests are actually measuring. Often it's properties of the raw converter or jpeg engine and not the capabilities of the camera design.

Oct 08, 2008 at 01:53 PM

Karl Witt
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p.1 #6 · Red noise 40d

I know this is an old post but I just came across it and have a thought

Vintage car, there was a type of paint job applied called 'webbing' that is somewhat similar to what is found on some boat bilge fiberglass areas. To me, this is not showing noise but an actual type of 'Vintage' paint work.

I could be wrong but just wondered if you had another shot of the samw car on the sunny side

that would verify noise or paint??

Karl

Nov 26, 2008 at 07:30 PM

dslrintraining
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p.1 #7 · Red noise 40d

I don't know I think it's just because it's under exposed. This car is the ONLY GTO race car that hasn't been restored. It's got original paint. The woman who owns it races it at vintage events regularly.
100% crop of correctly exposed hood.
This image is copyrighted by the owner

The whole picture
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Nov 26, 2008 at 09:08 PM


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