Sorry I haven't posted for a while. Life's been pretty crazy around here.
Whenever I see a question posted about one of the third-party noise reduction programs (Noiseware, Noise Ninja, etc), I always hasten to give this advice: Always utilise the noise reduction sliders in your Raw program first. They mightn't do a perfect job every time, but they can certainly help. One of the golden rules of editing is to do as much in Raw as possible before moving into Photoshop, and noise reduction is no exception.
So I'd like to share my approach to the noise reduction sliders. A couple of things to mention first:
1. I'll be discussing Adobe Camera Raw, because that's what I use. I'm quite sure the behaviour is the same in Lightroom, and I bet it's not too dissimilar in Aperture, DPP, etc.
2. At the time of writing this, I haven't tried ACR 6 in CS5. I'm told the noise reduction is much improved, with the addition of some new sliders. Once I've tried it, I'll update this post. The screenshots you see herein are CS4, and the methods are relevant for all previous versions.
3. Yes, this applies to Photoshop Elements, too.
Ok, let's start. If you've ever dabbled with noise reduction (of any sort) you'll know there are two controls for it - Luminance and Color. In ACR, the default values for the sliders are 0 and 25 respectively:
It's important to understand the difference. Luminance noise is what we think of when we usually think of noise - graininess. Here's a close-up example of luminance noise:
Colour noise is that underlying speckled colour (usually red and green, but can be blue as well) that is sometimes visible "below the surface" so to speak. Here's an exaggerated example:
And here's an example with some of each type of noise:
(Note: I've shown the above examples at 200% size, for impact. Normally you'd only view at 100%.)
As I mentioned earlier, the Adobe defaults for these sliders are 0 for luminance, and 25 for colour. I've always found these to be appalling settings. 0 is almost always too low for luminance, and 25 is invariably too high for colour.
Never forget the risk involved in noise reduction. There's a point at which noise reduction becomes detail reduction. If you push it too far, you start to cause damage to the desirable detail in your image. Obviously, this is counter-productive. It's not such a problem for luminance noise reduction, because even an inexperienced eye can tell when the reduction is too strong, and bring it back a bit. But the damage caused by too much colour noise reduction is much less obvious, and I frequently see examples of images being robbed of "good colour" because of that horrid default setting of 25 on the Color noise slider. I'm here to tell you that a much lower setting is usually suitable.
It's very difficult to tell at a glance which type of noise, and how much, is in an image. Colour noise is particularly hard to manage. But I've found a simple step-by-step process which gives me the best possible results every time.
Step One: Do your normal tonal edits first
Don't worry about noise at first. When you initially open your raw file, concentrate on the usual stuff - white balance, exposure, etc. It's easy to misjudge the severity of noise if the exposure isn't right.
Step Two: View at 100%
Double-click the Zoom Tool to enlarge your view to 100%.
Then use the Hand Tool to move the image around so you can see a suitably noisy area. Noise is most prominent in shadows, so choose a moderately dark area to view.
Step Three: Access the noise reduction sliders
In ACR, they are under the Detail tab.
Step Four: Set the sliders to 100/0
Set the Luminance noise slider to its maximum setting, and the Color noise slider to its minimum setting:
In a lot of cases, this is likely to be too much luminance noise reduction, making things ridiculously smooth. It's also likely to exaggerate the colour noise. That's exactly what you want at this stage. By temporarily taking the luminance noise out of the equation, it allows you to make the best possible judgment call about the colour noise.
Step Five: Gradually increase the Color noise slider
Starting at 0, increase the colour noise reduction by 1% at a time (I use the arrow key for this). The goal is to go just far enough to remove the colour noise, and no further. Remember, too much colour noise reduction starts to impact the good colour in your pixels.
Step Six: Gradually decrease the Luminance noise slider
From 100, bring the luminance noise reduction down to a satisfactory level.
Luminance noise reduction is largely a matter of taste - if you like very smooth images, you might leave this slider fairly high. But remember to check on things like hair and eyelashes, to make sure you're not smoothing out important detail.
Step Seven: Toggle the Preview
Turn the Preview checkbox on and off a few times to see the result of your noise reduction. Pan around the image a bit to check the effect of your settings on various parts of the image. Adjust as necessary.
Step Eight: Pause for a reality check
It's easy to get carried away with pixel-peeping, and begin to think that all noise is evil. Fact is, it'll be nowhere near as visible in print as it is on your screen right now. And it will completely disappear when you reduce your image for posting on the web. Be satisfied that you've smoothed it as much as you can, then get on with your day. There are much worse things to worry about :)