Today’s Question: To reduce noise in a photo, do you ever reduce Black levels?
Tim’s Quick Answer: Yes, in some cases I will darken the shadows in an image to help hide noise, provided I am actually happy with the degree of contrast involved with such an adjustment.
More Detail: Noise will generally be more prevalent in dark areas of an image, because those areas contain less information. In effect, noise is the opposite of information in the context of a photo. Bright areas have more information, and therefore less noise.
When you’re not able to adequately reduce the appearance of noise using noise reduction adjustments, you can help hide that noise by darkening up the darker areas of the image. That could mean darkening up the black value for the image, or darkening shadows in general.
Of course, I don’t want to exaggerate contrast or make an image appear too dark just to hide the noise. So I would only want to take this approach for an image where I intended to darken up the shadows regardless of the noise.
In other words, the motivation is often reversed here. I don’t generally decide to darken the shadows in an image to hide the noise, but rather feel a sense of relief when my intended darkening of the shadow areas also helps hide any noise that appears in those areas.
This is particularly an issue for luminance noise. Generally speaking, you can achieve great results reducing color noise for most images. Luminance noise can be a particular challenge, because reducing that luminance noise will have the side effect of reducing texture and detail, causing a loss of sharpness in the photo.