Radius slider help

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MorganP

Well-known member
Lightroom

Can some help me understand how to use the Radius slider under sharpening. I understand this refers to how many pixels the shaping goes out from the edge. When I hold down the (ALT) key and move the slider how do I know what is the correct level to use and how do I know when I’ve gone too far?
 
When I hold down the (ALT) key and move the slider how do I know what is the correct level to use and how do I know when I’ve gone too far?
A lot of this comes down to practice and experience but the key things to look for with the Radius slider are sharpening contours that are so wide that they overlap one another in areas of fine detail (e.g. fur, feathers, eyelashes) or contours that become so wide around main edges that they leave an obvious halo around your subject or major parts of your subject like antlers or beaks for wildlife images. The Alt trick key can help show you how wide those contours are getting but there's no exact line as to what constitutes too wide and it depends on things like the specific image and the image resolution.

One trick to seeing the impact of the Amount, Radius or Detail sliders is to temporarily jack all three way up (which will look terrible) and then work from the bottom up:

- Reduce the Detail slider while looking zoomed in on an area of out of focus background and adjust it down until you're not increasing the amount of noise in those areas.

- Pan the zoom box over to an area of fine in-focus detail like feathers, fur, eyelashes or something similar and reduce the Radius slider until the sharpening contours don't overlap one another in those areas. The Alt key trick can help here to see how wide those contours are getting and if they'll obviously lead to wide halos around major edges or start overlapping one another in areas of fine detail.

- Then go up to the Amount slider and adjust the overall sharpening to taste. I like to look at areas like grass and fur and if it has a sharp and uninviting look I'll back down the Amount slider. When in doubt, less is more with sharpening so if you're not sure it's usually best to back it down a touch. IOW, if summer grass looks like I'd cut my feet open walking barefoot on it or if the soft fur on an animal looks like a Brillo pad then I've gone too far and will back down the amount and or radius sliders.

I sure don't do this with every image but it's a good way to get a handle on the impact of each control.

The sharpening controls in LR are actually pretty well limited in their range compared to the same controls in the Unsharp Mask in PS (where the Detail slider is called Threshold), it's a bit easier to apply that bottom up sequence in PS where it's easier to push the controls too hard and see when you've gone too far and then back them off.

Generally speaking when I sharpen a decently sharp image in LR I'll usually end up with something like: Amount around 30 to maybe 50, Radius around 0.7 to maybe 1.5 pixels and Details down around 0 to maybe 20 to 30 or so depending on how much fine detail is in the image saving the higher values for images with a lot of fine detail that needs sharpening and using lower numbers when I want to restrict sharpening to the major high contrast edges.
 
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FWIW - in Steve's LR noise reduction workshop he details all of the sliders in the details module. The sharpening, detail and radius tools are interlinked and fully covered. However, it is one tiny part of the course so DR wyoming's post might be all you want.
 
Just to pile on, if you hold the alt key while moving the radius slider you see the impact of the radius more clearly. Watch the 'halo' near the edges and find the spot with good sharpening but small halo. Usually 1 or less and don't overdo the sharpening amount since you can also sharpen again in Photoshop depending on what you are doing with the picture. Also hold alt with the masking slider. You don't want to sharpen everything, especially not the background. As you slide white areas are impacted by the sharpening but black areas are masked from being sharpened.
 
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