Strange Artefacts - what are they?

petersmart

petersmart

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I often shoot at a high ISO (1600 ISO) on my Canon 450D and use Neat Image to get rid of noise.

This has shown up a problem concerning these artefacts:



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I had assumed that these were a by-product of using Neat Image, but in fact when closely inspected they are actually on the RAW files though heavily buried in noise - what Neat Image did was get rid of the noise revealing these artefacts.

Can anyone tell me what these artefacts are and how I can get rid of them?

Please note: These are definitely NOT a by product of Neat Image.

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They look like dust but the dust would be so far out of focus as to be invisible I would have thought. Strange that is.
 
I have seen this effect using Neat and other noise reduction software. It only occurs when I really push it. i.e like you high iso's or when I have tried to get detail from shadow areas etc.

On some shots you may get away with it.
 
But these artefacts aren't actually caused by Neat Image they are revealed by Neat Image removing all the noise.

I've spent a lot of time trying to sort out this problem thinking it was NI causing them but it isn't.

They are actually present on the RAW files.

Which is really weird.

Must admit I wondered about dust but if it is then I have a REALLY filthy sensor!

The only other thing I can come up with is that the sensor itself is producing them.

Of the two I must admit dust is the more likely (I think).
 
I had a lot of trouble with dust on the sensor with one camera but it wasn't anything like that, unless you shaved over the camera with the lens off. There's a few dots that look like dust though.

Dust on the sensor does show up because strictly speaking it's not on the sensor, it's on the glass protective plate that sits over the sensor. Dust tends to show up less with open lenses, more and sharper when you stop down. You could rule that out at least by doing a few test shots against light grey at steadily increasing f-stops.

Any chance of seeing a section of the raw?
 
Dont really know what could cause that but if its showing up on the RAW files it's going to be caused by the sensor or something on the lens.
 
Post a raw file up for us to download, so we can have a better look
 
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