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Techniques to reduce image noise

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Old Tuesday 5th February 2008, 18:39   #1
ikw101
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Techniques to reduce image noise

I'm sure we'd all prefer to shoot at ISO 100 but a combination of long lenses and poor light usually conspire to prevent this. So what are the best techniques to reduce noise to a bare minimum?

At the moment I'm using auto iso up to a maximum of ISO 800, shooting in raw and cleaning up images in the photoshop neat image plug-in. On the whole this seems to work fairly well unless I need to severely crop the original image (last resort).

Whilst I believe the most recent models from both Nikon and Canon are notable for their high ISO performance outside of laboratory conditions is there really that much of a difference between the image noise of eg. D200 and D300 or 30D and 40D. In my experience as long as you're shooting raw getting the exposure spot on appears to be the single most important factor in reducing noise.
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Old Tuesday 5th February 2008, 18:44   #2
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In my experience as long as you're shooting raw getting the exposure spot on appears to be the single most important factor in reducing noise.
Getting the exposure right really is the key. I've found that when the exposure is spot on at ISO800 I don't need to do any noise reduction. If you're going to get it wrong go a bit over rather than a bit under, brightening an image defintely makes noise worse.
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Old Tuesday 5th February 2008, 21:17   #3
Roy C
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I go along with Peter, I try to expose to the right (without blowing the highlights of course) so that when I process I do not need to push the exposure. If you under expose and push the exposure during processing it will create noise.
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Old Friday 8th February 2008, 11:38   #4
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"As long as you are shooting raw" .... That has got very little to do with it. (Not nothing, just very little.) As mentioned by another poster above, the key is to get the exposure right, and get close enough to the bird so that you don't have to crop too much. People talk a lot of tosh about raw sometimes, sometimes I think it must be a new religion or something. You can shoot raw, JPG, or Polish sausage and, if your composition and exposure and technique are OK then you'll have a good shot. Mess any of those up and the shot is blown anyway. The particular format you happen to have saved the dud shot in doesn't much matter. (Unless you are hungry, in which case the Polish sausage is best.)
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Old Saturday 9th February 2008, 22:39   #5
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Took a photo of a stonechat against a bright sky recently, and unsurprisingly it turned out underexposed. When I pushed the exposure up in ACR, the noise became horrendous. This was on a D300 at ISO 800 I believe. To be honest I can still see noise at ISO800 even when the exposure is OK. I have to look for it a bit though; it lies in the darker tone areas of the bird, making it look dirty. See the great spotted woodpecker and blue tits in my gallery for example.

I too, have used neat image. At the moment I'm experimenting with noise ninja, as it seems to offer more tools for dealing with noise.
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Old Saturday 16th February 2008, 13:38   #6
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Interesting comments on the D300's iso performance. Even though it appears the D300 has a very good noise reduction system I suspect that Neat image is still better at reducing what noise there is. Whether or not they'd be any difference in a printed image is debatable.

Helios - the GSW and Blue Tits look fine to me and at iso 800 and probably hand held I would be very happy with the results.

Tannin - totally agree about the amount of tosh in the raw vs jpeg debate. Personally I prefer to shoot jpeg only but historically in camera processing has proved unreliable so for the time being raw it is. To be honest I'm hoping that with the better in-camera processing of jpegs within the D300 I'll be able to rely far more on jpeg with the use of raw for tricky exposure situations only. Like you said a dud shot is a dud shot. There's nothing more depressing than wasting a vast amount of time sitting behind a computer squeezing the last amount of information out of millions of pixels. I'd rather learn from my mistakes, get out there and try to get a good shot.
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Old Monday 18th February 2008, 11:48   #7
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I'd rather learn from my mistakes, get out there and try to get a good shot.
... yet, a Polish sausage mustn't be underestimated ...
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Old Monday 18th February 2008, 12:37   #8
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With raw tending to be 12-bit and jpeg 8-bit, if nothing else raw gives you some latitude when post-processing if the original exposure was slightly out.
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Old Tuesday 19th February 2008, 19:44   #9
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... yet, a Polish sausage mustn't be underestimated ...
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Old Wednesday 20th February 2008, 14:39   #10
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With raw tending to be 12-bit and jpeg 8-bit, if nothing else raw gives you some latitude when post-processing if the original exposure was slightly out.
Yes indeed.

By way of a Real World example of a benefit in using RAW, my current testing of Raw Therapee has involved pushing the Highlight Recovery tool very hard, and its ability to recover visible detail from an apparently completely blown part of the picture is nothing short of miraculous - far, far better than anything I can do with jpegs in CS3, for example (I know ACR and Lightroom can do a similar thing with highlight recovery in RAW files, but I'm not big on Lightroom or ACR).

This means I'm much happier to get close to the wire with my exposure (even to the extent of actually blowing one of the colour channels), confident that I can do a better job of recovering highlights from the RAW file than I could possibly do if the shot had been taken in jpeg.

RT's highlight recovery works by looking at all three colour channels. Often, "blown" highlights are only actually blown in one channel: RT's highlight recovery algorithms look at the data in the remaining channels and extrapolate/recreate the lost detail from data left in the channels that didn't blow, even though there might be no visible detail whatsoever.

Now, this doesn't disagree with Tannin's point that good exposure is good exposure regardless of the format of the image file, but my God! does this tool (and other similar RAW-based highlight recovery tools) make it easier to get a "histogram as far to the right as you dare" exposure.
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Old Thursday 21st February 2008, 13:23   #11
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I am trying this program but when I try to open a raw image from my Canon 350D, all I get is an error message and the program shuts down !
Any ideas what I`m doing wrong ?
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Old Thursday 21st February 2008, 19:23   #12
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You're using Raw Therapee, Andy?

Which version of RT? Which operating system on your PC?

And what error message do you get?

The 350D has been supported by Raw Therapee for a long time, so there's no problem there.

I'm guessing that you might have installed the wrong version of the software - there are "SSE support" and "no SSE support" versions of RT for newer and older PCs, and you might have the wrong one.
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Old Saturday 23rd February 2008, 09:27   #13
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People talk a lot of tosh about raw sometimes
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With raw tending to be 12-bit and jpeg 8-bit, if nothing else raw gives you some latitude when post-processing if the original exposure was slightly out.
Ahh, a perfect example. Not your fault, MBA, you have more than likely read that somewhere and absorbed it as one of those many useful little bits of information one accumulates over time.

Trouble is, it's complete tosh. The dynamic range of a camera is the dynamic range of the camera. No iffs, buts or maybes. The only difference between an 8-bit raw file and a 12-bit raw file taken under the same conditions with the same camera is that the 12-bit file has smaller graduations. It's exactly the same as measuring the boiling point and freezing point of water: if you measure in Fahrenheit (think 12-bit raw) there are .. er .. 212-32 = 180 degrees between boiling and freezing, if you measure in Celsius (think 8-bit raw) there are only 100 degrees. But because the degrees are different sizes, the actual temperature of the water is exactly the same.

The size of the unit you describe the output in doesn't make any difference at all to the dynamic range. You could have 8-bit raw, 12-bit raw, 2-bit raw, or 768-bit raw, the maximum light level the sensor can record and the minimum light level it can usefully record remains the same.

Raw does have a (small) advantage in dynamic range over JPG because in-camera JPGs are usually sampled from a subset of the total available raw data - i.e., the JPG engine throws a small part of the brightness information away, but this has nothing at all to do with the"bitness" of the raw processor.
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Old Sunday 24th February 2008, 13:46   #14
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Ahh, a perfect example. Not your fault, MBA, you have more than likely read that somewhere and absorbed it as one of those many useful little bits of information one accumulates over time.

Trouble is, it's complete tosh. The dynamic range of a camera is the dynamic range of the camera. No iffs, buts or maybes.
Wow, friendly response. It's good there is someone here who has the definitive answers, no room for disagreement or debate.

Trouble is, in the post you replied to there was no mention of dynamic range. Actually the OP's point was correct. Raw is 12-bit, which provides more information than an 8-bit JPG (e.g. 4096 colours per colour channel instead of 256). It also has not committed the exposure, WB etc to the file, thereby allowing more latitude to adjust in post-processing. Exactly as he said.
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Old Sunday 24th February 2008, 22:43   #15
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Hi Moadib. Dynamic range it is indeed what we are talking about here. When we say we have "a badly exposed picture", what we are really saying is that the range of light intensities we have attempted to record does not fit within the range of light intensities the system is capable of recording.

It makes no difference how many numbers you use to describe a blown-out highlight; if it is outside the dynamic range of the sensor, it is outside the dynamic range of the sensor. End of story.

Eight-bit raw will describe the blown-out parts of the picture as 255, 255, 255, 12-bit raw will describe them as 4095, 4095, 4095, but there is still nothing you can do to make a good photograph from it. The same applies at the under-exposure end of the scale.

It is perhaps natural to think that a 12-bit file "must be" capable of recording a greater spread of brightness information than an 8-bit file - hey, it has more numbers, doesn't it? - but quite wrong. The end-points of the two recordings are in exactly the same places - i.e., pure black (0 in 8-bit and 0 in 12-bit) and pure white (255 in 8-bit and 4095 in 12-bit). The dynamic range is the same, thus the ability to recover from over or under exposure is the same.
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Old Tuesday 26th February 2008, 09:58   #16
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the range of light intensities we have does not fit within the range of light the system is capable of recording.
Tanin’s spot on here with colour range. To me this is the most important aspect of a camera, ‘to record accurately the subjects colour’. Colour range is rarely mentioned about individual cameras and accurately illustrated when the press reviews a camera.

Noise isn’t a problem, if you have it, then you done or doing something wrong.

The major drawback with digital is still the ‘mudding’ of colours with excessive black. The causes are many, both pre and post production.
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Old Tuesday 26th February 2008, 23:55   #17
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Hi Moadib. Dynamic range it is indeed what we are talking about here. When we say we have "a badly exposed picture", what we are really saying is that the range of light intensities we have attempted to record does not fit within the range of light intensities the system is capable of recording.

It makes no difference how many numbers you use to describe a blown-out highlight; if it is outside the dynamic range of the sensor, it is outside the dynamic range of the sensor. End of story.
Dynamic range is what you were and are talking about, but it is not what the OP was talking about. His point was about RAW's greater flexibility in post-processing whether that be dynamic range, white balance, noise, colour, flexibility whatever. It is not simply a point on light intensity. The OP remains correct. RAW is not for everyone, nor every situation, but it does fit those criteria
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