Reduce Noise in HDR Images with Masked Reduction
Tone mapped images don’t always come out of your favorite high dynamic range (HDR) application looking perfect. In fact, most of the time, they need further editing before they’re “perfect.” Some images have too much noise (a common problem with HDR) in general, or they may need different levels of noise reduction in different areas.
The next step up the ladder of sophistication is masked (or erased) noise reduction. This works very well for landscape shots with a good deal of sky and possibly water. Here’s how:
Duplicate the layer you want to make the adjustment on.
Choose Filter→Noise→Reduce Noise.
From the Reduce Noise dialog box, choose the noise reduction options you want and then click OK.
Make sure the reduce noise layer is active, and then erase the areas you don’t want noise reduction applied to.
You can choose a few different methods to erase areas from the noise reduction layer. This blends the reduction in with layers below that have no noise reduction applied.
Select and delete. Switch to your favorite selection method, select areas to erase, and then delete them.
Select, invert, and delete. Sometimes it’s easier to select the opposite areas. For example, the sky tends to benefit from noise reduction much more than trees and the ground. In this scenario, using the Magic Wand to select areas to delete (trees and the ground) is almost impossible because those areas have too much texture and variability.
It’s far easier to use the Magic Wand to select the sky, invert the selection (choose Selection→Inverse), and delete.
Erase. Switch to the Eraser and erase the areas of the layer you don’t want to see.
Elements offers a few different erasers. The standard Eraser is manual mode. There are also the Background Eraser and the Magic Eraser. The Background Eraser erases material similar to where you first click and erase in the image — it assumes you are erasing the background. The Magic Eraser acts like the Magic Wand. Click an area you want to delete, and presto! — it’s gone!
Opt for the combo platter. You can use the Lasso tool to quickly outline areas you want to delete. The trees and buildings in this scene don’t need noise reduction, so they can be deleted from this layer. The layer beneath — the Background in this case — shows through and preserves their sharpness. This is a rough selection. No need to spend an inordinate amount of time on it.
You can then use the Eraser in Brush mode to fine-tune the border, as shown in this figure, changing brushes to suit the conditions. Don’t let yourself get too wrapped up in precision here. It’s important not to be sloppy, but the border doesn’t need to be exact.
That’s the beauty of blending. You can go over the lines a bit into the sky to make sure the edges of the trees aren’t softened, and you just don’t have to worry about the part of the sky that gets erased.
One big (and negative) difference between Elements and Photoshop rears its head when you try to figure out how to alter a brush’s hardness in Elements. You can’t (for most, that is — the Background Eraser and Healing Brush are two exceptions).
Change hardness for the normal Eraser in Elements by selecting different brushes or switching the Eraser mode from Brush to Pencil or Block.
Perform a merged copy and continue working.
This consolidates the effects of the blend into one solid layer.