Today’s Question: Can you explain how the Detail, Contrast, and Smoothness sliders work in Noise Reduction [for Adobe Camera Raw or Lightroom]?
Tim’s Quick Answer: The Detail and Contrast sliders for noise reduction in Camera Raw or Lightroom enable you to improve the degree to which detail is maintained in the image, though at the risk of introducing other visible artifacts in the image. The Smoothness slider improves the blending of any color artifacts that remain based on the current noise reduction settings.
More Detail: The primary control for noise reduction in Lightroom or Adobe Camera Raw is the Luminance slider for luminance noise reduction and the Color slider for color noise reduction. These sliders provide the strength control for noise reduction.
In addition, there are several controls that enable you to fine-tune the overall behavior of the noise reduction effect.
There is a Detail slider for both luminance and color noise reduction. These both provide the same basic capability, just focused on luminance versus color noise reduction. Increasing the value for Detail increases the threshold for when noise reduction is applied in an image. In other words, with a higher value, detail will be preserved by virtue of the noise reduction not applying (at least not as strongly) along detail edges in the photo.
The risk of increasing the value for Detail, however, is that noise may be revealed in the image. This can be especially problematic since the noise will appear in small areas (even individual pixels), causing it to stand out a bit more clearly.
The Contrast slider is only available for luminance noise reduction, and is similar in concept to the Detail slider, but focused more broadly on contrast rather than fine detail. If the noise reduction is causing midtone contrast to be reduced, you can increase the value for Contrast. However, you will need to keep an eye out for splotchy artifacts with a value that is too high. For smoother detail (with less contrast) you can use a lower value. In other words, you need to balance the setting based on trying to improve contrast without creating a mottled appearance in areas of the image.
The Smoothness slider is only available for color noise reduction, and it is focused on reducing color artifacts that remain after applying color noise reduction. When you reduce color noise, you will often see that noise represented by individual pixels gets blended so that instead you have blotches of color artifacts. Increasing the value for Smoothness will blend those artifacts, often removing their appearance altogether. In general it is relatively safe to use a high setting for Smoothing, but you’ll want to watch for blending of colors along contrast edges in the photo.
The effects of these refinement controls can be more easily seen if you apply relatively strong noise reduction to an image with extreme noise, as a test for getting more familiar with the actual effect in the photo.