At one time or another, digital photographers will have to deal with image noise. This is particularly true when photos have been shot in dim lighting conditions and at a high ISO. Many digital cameras produce visible noise above 400 ISO. The newer generation of cameras are able to better handle image noise than previous models, but in the event there's a need for a quick fix, either for images from old camera models or the newer ones, it's good to know that we can rely on Aperture's built-in Noise Reduction tool to help us perform a non-distructive edit.

Digital cameras suffer from two types of noise: luminance noise and chrominance noise. The speckled patterns you see in your images is referred to as luminance noise. This is characterized by obvious change in brightness (or luminance) among adjacent pixels. On the other hand, chrominance noise, or color noise, appears as unnatural splotches of colored pixels. Luminance noise will typically appear more obvious than chrominance noise.

To begin fixing the noise on an image, zoom in to 100% view. Applying noise reduction, and also with sharpening, is best done on a 1:1 view. Click on Noise Reduction from the Add Adjustments menu. The "controls group" of Noise Reduction will be added to the Adjustments HUD. To fix the photo, use both the Radius slider and Edge Detail sliders. The Radius slider lets you decide on the size of the noise that will be reduced. The edge Detail slider gives you control over how much edge details to preserve. You can keep on adjusting both the Radius and Edge Detail sliders until you get the desired results.

In addition, you can apply noise reduction before or after sharpening. In order to get the best and most balanced results, and because of Aperture's non-destructive editing, you can continue to refine your adjustments even after you've already initially applied these enhancements.

It is generally agreed that there is no one perfect way to apply noise reduction. Within a generally accepted range, some photographers prefer aggressive adjustments while others like a more subtle approach. At the start, you might want to experiment a bit until you eventually get the hang of it. But one thing to keep in mind when applying noise reduction, which is the same for sharpening, is to keep the output in mind. You reduce the noise and adjust sharpening in relation to what the final output will be. This means that, to get the best result, the level of sharpening that you apply may be different from one output to another from a single image.