Hands on: Reducing noise in pictures

The Remove Noise tab has three Noise Correction sliders – small, medium and large – which work on pixel clusters of different sizes.

The small and (to a lesser extent) medium sliders do a good job of reducing noise while maintaining image detail.

The large one does a lot of collateral damage and so I tend to leave it alone. For all but the worst cases, you won’t need to set any sliders beyond 50.

Below the noise correction sliders are two further controls labelled Correction Blend and Sharpening. The first of these blends the noise-corrected image that you see in the preview thumbnail with the original, reintroducing some of the image detail that may have been lost in the process. The second, as far as I can see, applies the unsharp mask filter.

These tools provide a quick fix and you might want to use them if you’re defining a filter preset, particularly for use in a batch process. But for individual images, I prefer to leave these set to zero. If you duplicate the background layer before applying the filter, you can use the layer opacity and blend controls to better effect.

You can also use mask layers to restrict the filter to only those parts of the image that require it. Alternatively, if you’re looking for a quicker, more automatic way to restrict the filter, try the Protect Image tab. This uses a hue map to define a range of hues that you can protect from the actions of the filter. As noise is mostly confined to shadow regions, if you confine it to the lighter toned hues it can be quite effective.

Photoshopping noise
Photoshop’s Reduce Noise filter is a more straightforward tool than Paint Shop Pro’s, at least in basic mode. There are four sliders controlling Strength, Preserve Details, Reduce Color Noise and Sharpen Details. While it’s not impossible to go over the top with Photoshop’s Reduce Noise filter, it’s a more subtle tool than Paint Shop Pro’s. Even if you max out all the sliders, you’ll get an improved, though slightly soft image.

In advanced mode, you can apply the filter to individual colour channels. Noise is usually more pronounced in one channel – usually, but not always, blue – so by restricting the filter to that channel, or at least applying more noise reduction to that channel than the others, you can achieve better results with less overall image softening.

If you intend to use this feature, first (in Photoshop) press Ctrl & 1, Ctrl & 2 and Ctrl & 3 to view the red, green and blue channels respectively and identify the channel with the worst noise problem.

Applying noise reduction to individual channels is an effective way to reduce noise while retaining image detail. If your image editor or noise plug-in doesn’t provide individual channel adjustment, apply it separately to the channels that require it. This may involve splitting the image into its constituent red, green and blue channels, then recombining them after applying the filter.