Separate Your Highlights and Shadows
Here’s an image shot from the inside of a cave. The light areas are a little blurry and need some sharpening and the dark areas inside the cave show some noise. Here’s how we’re going to fix both those problems.
First, we’re going to isolate just those shadows and remove the noise from there without affecting the rest of the image, then we’re going to use the same technique to isolate the mid-tones and highlights of the lighthouse and sea and sharpen them up.
How to Reduce Noise in the Shadows
Duplicate your image layer. If you have several layers from an image you’ve been working on, you’ll need to create a stamp (Shift+Option+Cmd+E on Mac or Shift+Alt+Ctrl+E on PC) of all the visible layers. Call this duplicated layer “Reduce Noise”.
Go to Filter > Noise > Reduce Noise. Zoom in on a dark area where you see the noise and dial-in numbers for the sliders that clear out the noise you see there. When you’re happy the amount of noise reduction in the preview window, click ok.
The whole image will look relatively blurred now with the noise reduction, but we’re going to fix that now.
Double click on the “Reduce Noise” layer to open up the layer styles pallet. Turn on Colour Overlay and set it a bright colour not present in your image. I selected a bright yellow. This is just to see which luminance values are affected in the next step. We’ll turn this layer style off when we’re done. For now, just pick any bright colour. This will paint your whole image with that bright colour.
Still in your layer styles pallet, click “Blending Options” at the top of the left column. Here you will find your “Blend If” options. On the “Underlying Layer” slider, grab the white slider on the left, and drag it to the right. You will see the highlights of your image start to appear from under your Colour Overlay colour.
Hold down the Option key on Mac or Alt key on PC, then click and pull the left half of the white slider to the left to separate it into two halves. Pull the left half of the slider further to the left to soften the effect. The parts of your image still covered my your bright overlay colour will be the parts of the “Reduce Noise” layer which will still be visible.
When you see you have all your shadows selected (they will be covered by your Colour Overlay colour), click ok then turn off the visibility of the “Colour Overlay” effect on the layer.
You will see now that your “Reduce Noise” layer only affects the shadows of your image, leaving the mid-tones and highlights untouched. You can dial back the strength of this effect using the opacity slider if needed.
How to Sharpen Mid-tones and Highlights
Let’s sharpen up the midtones and highlights using the same method. Create a stamp of the layer to create a new layer of all your visible layers. Call this layer “Sharpen”.
Go to Filter > Sharpen > Smart Sharpen.
Dial in the settings to sharpen your image as needed. Just focus on the mid-tones and highlights of your image. When you’re happy with the amount of sharpening you have, click ok.
Double click your Sharpen layer to open your Layer Style dialogue box. Once again, turn on Colour Overlay so you can see where your Blend If sliders will affect your image.
Click on “Blending Options” again in the right panel and adjust your Underlying Layer sliders. This time we only want to affect the mid-tones and highlights so look for your Colour Overlay colour to cover just those tones. Move the black slider on the left of the Underlying Layer section to the right. Split the slider in two to feather the effect. When you’re satisfied all the areas you want to be sharpened are covered by your Colour Overlay colour, click ok.
Turn off the Colour Overlay effect on the layer. See how your sharpening is only affecting the lighter areas of your image while ignoring the darker areas. Dial back the strength of this layer using the opacity slider if the sharpening is too much.