Noise Reduction Methods (IQ #2)

Welcome to the second in a series of articles aimed at improving the IQ (Image Quality) of our cameras. Today's topic is noise reduction methods.

What is Noise Reduction?

Noise Reduction (NR) is a set of tools for the photographer to use. Image noise generally comes from shooting at high ISO speeds on your camera. Typical noise reduction tools include dedicated NR software and filters. For this tutorial, we'll be focusing on using NR software in Adobe Photoshop CS2. (Latest version: CS3)

The NR program I used in this tutorial is Noiseware Professional Plug-In, but any good NR software will do. Before using Noiseware I was using Neat Image for a very long time, you may want to try that. You can also use the noise reduction filter in Photoshop, but I don't recommend this. It isn't as good as dedicated software.

First Things First

Firstly, you need to open your image. Find yourself a noisy image to try out different techniques. As I said I'll be using Noiseware but you can use any decent NR program. Noiseware and Neat Image both supply free versions of their software if you want to use those. You don't even have to use Photoshop, as they offer standalone versions of their software. I used Noiseware's Photoshop plug-in version to try out different strengths of NR and combine them with other filter effects.

the Luminance slider affects the grain-type noise, while the Color slider affects the coloured noise

Once it's open, try out different noise reduction strengths. The Luminance slider affects the so-called “salt and pepper” type noise; this is monochromatic and much like film grain. The Color slider affects the more “digital-like” noise. This typically looks like unsightly coloured blotches (called chroma noise). With both sliders, moving it right increases the noise reduction, and moving it the other way decreases it.

Keeping the Detail

often, an image which you thought was far too noisy turns out great with a quick pass through NR software... what they're capable of is astonishing

At this stage, it's important to try achieve a balance between noise reduction and image detail. Very often the automatic settings do a great job here. By applying more noise reduction you sacrifice more and more and detail. Once everything's fine and dandy click ok.

Once you compare to the original you'll realise what a huge difference some NR can make. Often, an image which you thought was far too noisy turns out great with a quick pass through NR software. What they're capable of these days is rather astonishing.

Using the “Faux Detail” Method

If you're happy with the resultant image, keep it. You can try this technique if you're not completely happy yet, or just want to learn a new technique for later down the road.

Once you have your image, apply some very strong NR to it. Adjust your sliders a long way to the right. This will create a noise-free image (or almost), but will have lost tons of its detail in the process.

There is a way to create some “faux detail”, making it seem as if the image is grainy but detailed at the same time.

After you've applied the strong NR, go to Filter >> Noise >> Add Noise... Apply the following settings:
— Amount: around 4%
— Distribution: Gaussian
— Monochromatic (important)

Once you apply this filter, you'll see the image come to life. Before it seemed to be botched and lacking detail due to aggressive noise reduction, now it'll appear to be full of detail yet not too bad in the noise department. I'm not sure exactly how this works, but I think this is because the added noise is working to mask the lack of detail, thus tricking the eye into believing that it's actually very detailed.

Below is a noisy image taken with my Nikon D40. It was taken at ISO Hi-1, equivalent to ISO 3200. It shows the image at various stages. The first is the original, untouched image. The second has been processed using the method described in Keeping the Detail, and the last has been processed using the Faux Detail method.

the last one looks the best... it looks cleaner, with less noise and more detail

In my opinion, the last one looks the best in this particular example. Especially around the double-0 button, it looks cleaner, with less noise and more detail. The noise that is there seems to be of a finer quality.

Try this technique on your own images and see which works best for you.

Final Tip

By the way, it's very important to try and get your images as untouched as possible when shooting in high ISOs. This means shooting in raw mode and disabling any in-camera NR that may be occurring. What the camera has to do in less than a second, your computer can do in a lot more time and using specialised tools. It's better to leave the noise reduction to your powerful NR software than your camera or raw converter. For digital compacts, it's going to be difficult to get any sort of result from them. In this case try your best with what you've got.

That's it for this edition of IQ. I hope you learnt something, see you another time!

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