[Leica] CS2 and noise reduction.

[firkin at ncable.net.au (Alastair Firkin)]

Well, I'm not really able to give you a techie answer, but my "vague" 
interest stems from the idea of packing a small digital camera on my 
upcoming trip. Because I'm not going to spend a fortune on the sensor, 
I expect there will be some "noise" in the image.

Noise first came into my life when I started Radiology and began 
dealing with "digital" technologies especially CT. At the limits of the 
detectors capabilities, the "formula" which created an image from all 
the data, could not tell the difference between the human tissues and 
the "noise" inherent in the system. If you increased the amount of 
radiation you got more "signal" and relatively less "noise", and it is 
the signal you need.

So with the little sensors and cheaper sensors, they need lots of 
photons to "hide" the speckle into the background: it will still be 
there, only it will not be as obvious. As the photons fade, the noise 
comes out and eventually, you will lose all signal.

As far as I can see, the noise filters look at the "pattern" made by 
the background of noise and try to remove those pixels from the image 
replacing them with a mixture of what is left in the neighbourhood. If 
you remove to much "noise", you will fill in the gaps with rather too 
much "filler" and end up with an image which looks as if it was being 
painted in.

If you can remove noise only, the image will be more accurate and 
contain only "signal", but there will always be a compromise.

Cheers


On 09/02/2006, at 8:38, Ted Grant wrote:

> It would be great if in simple language some one will explain this 
> question. Considering this is a question from the dimwit level.
>
> Please explain how some of you people have a noise problem and I've 
> only seen it in a few picture situations where I suppose I pushed my 
> luck in almost available darkness situations and near blew the shot?
>
> I'll tell you what really really ticks me off no end is, to have some 
> techie guy look at one of my 13X19 colour photographs shot by 
> available window light, soft gentle beautiful light, a portrait type 
> photograph of a young lad like many of us shoot. And jaw on about 
> "noise" here, there and a few other places in the print. And for the 
> life of me I can't see what the hell he's talking about.
>
> Now he's looking at the print from maybe 6-8 inches away, for the life 
> of me I try my hardest to see and understand this stuff because I 
> really did want to learn from this fellow. But all he did was royally 
> piss me off no end with his "noise poppy cock numbers and meaningless 
> words nonsense!"
>
> I took the print from him, held it at a normal viewing distance for 
> it's size and asked a simple question. "How does it look as a 
> photograph?" His immediate response, "Oh my gosh it's a beautiful 
> photograph!"
>
> My response... "So what's all the bull shit about noise viewed at 6 
> inches from the print if you're so impressed with the photograph 
> viewed at a proper distance for size?"
>
> His response?.......... no answer! He either didn't know or appeared 
> more than embarrassed! I opted for just another numbers guy!
>
> So OK already, what's with the noise stuff? I know it's supposed to be 
> found in dark areas, but if you shoot it correctly in the first place, 
> why would there be any screwing around trying to get rid of something 
> you can't see unless yer 6" inches or less away from the print?
>
> Be nice now, I'm not trying to be a smart ass, I really want to know 
> about this noise thing because quite frankly I've yet to see what the 
> heck you are talking about. Well Ok I suppose in a couple of badly 
> printed photographs where I over tweaked it without knowing what I was 
> doing. Like under what conditions do you see this quite obviously?
>
> Remember, keep it simple as though you're speaking with someone who 
> only understands this is a computer screen, not a TV set. ;-)
> ted
>
>
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>
Alastair