Taking Control of Sharpening in Lightroom

September 21, 2013  •  5 Comments

This article discusses an image sharpening strategy found in Lightroom but also uses illustrations that highlight the importance of applying image sharpening in a selective manner when necessary. This Lightroom feature is a staple in my image processing workflow! 

The basis of this Lightroom sharpening strategy is to ensure that you apply sharpening only to targeted areas of an image and avoid sharpening areas of an image that contain noise, grain, or otherwise undesirable textures that should not be sharpened or accentuated otherwise. When people view your images, their eye will be attracted to sharp edges and areas of higher contrast. The last thing you want is to accentuate noise/grain, and add contrast to parts of the image that detract from your primary subject. Lightroom gives us an awesome feature in the Masking slider that allows us to literally see the areas of an image that is being targeted for sharpening.

Fig A: Click to enlarge See Figure A: Notice the Detail panel at far right. This is where you’ll find your image sharpening tools including the Masking slider. The Detail panel slider settings you see in Figure A are the Lightroom defaults for raw file conversion. Notice the Masking slider is set to zero. This means that no areas of the image are being masked from sharpening and subsequently the entire image will be sharpened equally. Depending on the image this may be a very bad thing!  

Fig. B: Click to enlarge See Figure B: The magic begins when you hold the ALT key (Option key on Mac) while clicking on the Masking slider. By doing this Lightroom will reveal the “mask” that can be applied to your image and visually shows you what areas will be sharpened and what areas will be masked. The idea of the mask is the same as with any image processing software that uses masks: “black conceals and white reveals”. This means that all black areas of the mask will be concealed (masked off and will not be sharpened), while all white areas of the mask will revealed (no mask applied) and will be sharpened. 

Stop. Pay attention to the noisy/grainy texture in the sky of Figure B. In this particular case the noise/grain is a result of underexposure in that region of the photo. And you will see the same sort of noise/grain from other images that have high ISO noise. In either case, you DO NOT want to sharpen or accentuate these areas of an image. Using the Masking slider will enable you to mask (conceal) these regions and constrict the sharpening mask down to edges that will attract the eye.

See Fig. C and Fig. D below: You will see the Masking slider has been advanced to 20% and 70% respectively. Notice how dramatic of an affect the mask has had on the noisy/grainy sky. At 20% the noise has been significantly reduced and at 73% the noise has been completely masked off. Also compare how the mask constricts down to the edges of the buildings and the moon as the Masking slider advances. These edges are the areas of the image that you DO want to sharpen and accentuate.

Fig. C: Click to enlarge Fig. D: Click to enlarge

Once you have applied an appropriate mask to your image, release the ALT key (Option key on Mac) and use the Amount, Radius, and Detail sliders to sharpen your image as needed. Although we have masked off a large area of the examples used here, you can still over-sharpen the areas of the image that were visible through the mask. My recommendation is to take it easy … a little dab’ll do ya!

TIP: Holding the ALT key (Option key on Mac) while adjusting the Amount, Radius, and Detail sliders will also reveal a mask that is helpful for evaluating the sharpening effect. 

Note: It is important to recognize that applying the sharpening mask does not remove noise/grain from your images – it only prevents the noise/grain from being accentuated when sharpening is applied. 

Below is Adobe’s definition of the sliders used for image sharpening in Lightroom:

  • Amount: Adjusts edge definition. Increase the Amount value to increase sharpening. A value of zero (0) turns off sharpening. In general, set Amount to a lower value for cleaner images. The adjustment locates pixels that differ from surrounding pixels based on the threshold you specify and increases the pixels’ contrast by the amount you specify.
  • Radius: Adjusts the size of the details that sharpening is applied to. Photos with very fine details may need a lower radius setting. Photos with larger details may be able to use a larger radius. Using too large a radius generally results in unnatural-looking results.
  • Detail: Adjusts how much high-frequency information is sharpened in the image and how much the sharpening process emphasizes edges. Lower settings primarily sharpen edges to remove blurring. Higher values are useful for making the textures in the image more pronounced.
  • Masking: Controls an edge mask. With a setting of zero (0), everything in the image receives the same amount of sharpening. With a setting of 100, sharpening is mostly restricted to those areas near the strongest edges.


Lady GooGoo La La(non-registered)
Thank you so much Kevin your effort is appreciated!

Lady GooGoo LaLa
Kevin Childress Photography
Hello, Lady! I hope this helps ...

I wouldn't apply noise reduction to any area of the image that didn't need it, so in that case I wouldn't recommend a global noise reduction. You really only have a couple options for applying selective noise reduction in LR. For a noisy sky I would first use a gradient mask to cover as much of the area as possible. Then, if needed, I would use a soft brush tip (medium feather and medium flow) to brush in noise reduction closer to the ground.

Tip 1) When using the adjustment brush, use the "o" key as a shortcut to display the mask overlay. Alternatively, you can enable or disable the mask overlay by clicking on "show selected mask overlay" when using the brush.

Tip 2) Be careful with the "auto mask" feature when using the brush. Turn the auto mask feature on and off while brushing across parts of the image where there are edges. You'll see how the auto mask reacts differently when crossing edges depending on this feature being enabled or disabled.

Tip 3) Apply the brush to all areas of the sky that you want to adjust (using the mask overlay) BEFORE you move any of the sliders in the brush's adjustment panel. Once you have the mask brushed in, then move whatever adjustment sliders you want to see how it effects the image.
Lady GooGoo LaLa(non-registered)
Excellent, Kevin, but what if I want to apply noise reduction on the sky.
Are the only options:
paint it all with an large adjustment brush, or
global noise reduction?
Kevin Childress Photography
Hello, Pat! Figure A is shown before any edge sharpening had been applied to the image. And I agree with your comment that fine detail like the noise/grain in the sky might not matter when viewed on a typical computer display or when displayed as a low-resolution image. Take for example that I display images on my website sized to only 800 pixels on the long edge. I could certainly get away with displaying a much more grainy/noisy image at that low resolution. As you suggest, the viewer would not likely be able to detect excessive noise/grain at that resolution.

To your second question: Lightroom has an amazing number of built-in keyboard shortcuts. When using the sharpening tools in Lightroom, the ALT key is only used as a keyboard shortcut for revealing the mask that is being applied to the image (literally to make the mask visible on the display).
Great explanation!

Question: I figure A before or after being sharpened? Although fine detail like that might not matter on a regular computer screen since it's resolution is likely much lower than a high res photo?

Another question: What is the purpose of holding the ALT key, does that allow you to preview as you make adjustments, or is this just the way Lightroom operates?
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