Reduce Noise in Selected Areas of HDR Images
A common problem with high dynamic range (HDR) images is that they have too much noise, or they may need different levels of noise reduction in different areas. You can reduce noise in HDR images just in selected areas of the image, rather than the whole image.
Applying noise reduction to an entire layer has its strengths and weaknesses. One big weakness is the fact that you might not need the same level of noise reduction across the image. This is definitely a factor for photos that contain a lot of texture and detail — trees, concrete, rocks, hair, and so forth.
One method to get around this is to select the noisy areas first and then apply noise reduction to those specific areas. The drawback to this is that selecting complex areas with any metaphysical degree of certitude is often very hard, which means you’ll end up with compromises, or it will take forever.
This figure shows an image taken from a bridge. The iron latticework makes for a tough selection. The attempt to select areas in which to reduce noise with the Magic Wand gives a poor result.
On the other hand, there’s not much difference between selecting areas versus erasing them in Photoshop Elements (as part of blending) or using a mask in Photoshop. The supreme advantage to a mask, of course, is being able to change the masked area after the fact. After all, after you delete something, it’s gone.
The tiebreaker often comes down to a desire to keep noise reduction isolated to separate layers, and blending the results afterward.