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Sharpening Basics

This Article Features Photo Zoom

A small amount of capture sharpening in a program like Lightroom or Adobe Camera Raw is a good place to start.

Nothing takes away from the beauty of a photographic print like poor sharpening. An image that's undersharpened makes details fuzzy and less appealing, while an oversharpened image just looks plain ugly and screams bad digital technique. A properly sharpened image focuses the viewer’s attention completely on the image and not poor Photoshop skills, which I would hope is the goal of very photographer.

All digital images, whether from digital capture or scans from film, need some degree of sharpening to define edges and properly bring out details in the image. To create sharp-looking prints (or monitor-based images for that matter), first start with good shooting techniques so that your images are sharp to begin with. Trying to sharpen an image that shows camera shake to begin with can be a trying exercise with mixed results. Use a tripod and cable release when shooting with slow shutter speeds, and if hand holding with faster shutter speeds, use image stabilization if you have it and learn how to shoot with steady hands, bracing against rocks or walls if they’re nearby.

Oversharpened image—see halos on the edges of the building and the tree.

At the dawn of the digital age, the sharpening gurus always suggested that no sharpening be done until output, because different print (or monitor) sizes need different amounts of sharpening—the larger your image file, the more sharpening. Now the consensus is that a certain amount of “capture sharpening” should be applied to RAW captures or scans. The theory is that a small amount of sharpening is necessary to properly display the image for making tonal adjustments. For my capture sharpening, I'm happy with the default settings in Lightroom and Adobe Camera Raw (ACR) pictured in the screenshot above. I find it adds a little crispness to the details in my images without creating weird halos (more about those later) along my big edges. The only time I stray from these default settings is for high-ISO images that might require noise reduction. Reducing noise can soften the edges of any image, so I’ll add some sharpening to these images to compensate for that softness, but never too much. I usually keep my sharpening amount under 75 even in these high-ISO images, and leave further sharpening for the output phase of my image processing.

A better attempt at unsharp mask for this image—notice the lack of edge halos.

I still do my final sharpening in Photoshop using the Unsharp Mask filter, but you can get similar results in Lightroom or ACR. The Unsharp Mask filter is a fairly simple tool once you get the hang of it. It has three sliders—Amount, Radius and Threshold. Increasing the amount adds sharpening. Increasing the radius increases the number of pixels out from an edge that's included in the sharpening, so a larger radius means more sharpening is applied. Threshold determines what an edge is by defining how different pixels must be in order for Photoshop to consider it an edge, so increasing Threshold actually decreases the sharpening effect. Used in tandem, the three sliders can properly sharpen any well-shot image. For digital captures, I usually set the threshold to between 0 and 2 and the radius to 1 (for scans, I’ll use a higher threshold of around 5, which seems to lessen the effect of sharpening on any film grain that was captured by the scan). I then adjust the amount slider until I get good detail sharpening without creating halos on my edges. As I mentioned before, the larger an image file, the more sharpening is typically needed. For low-res web use, I find capture sharpening often is enough, but if I apply an Unsharp Mask, I’ll keep the amount at 75 or lower. For big prints, say 24x36 inches, I’ll often push the amount to 300 or higher. These numbers are a good place to start, but every image needs a different amount of sharpening, so you’ll need to play around with the sliders until it looks just right.

If you prefer to use Lightroom or ACR for your sharpening, it works a lot like the Unsharp Mask filter. The Amount and Radius sliders are pretty much identical, while the Masking slider works like Threshold. There’s also a detail slider, which does what you would think, adding sharpness to the detail areas of an image. The wildcard in the Lightroom and ACR interface is the Clarity slider, which is located up above the Vibrance and Saturation sliders. Though not paired with the sharpening sliders, Clarity, which increases midtone contrast, also affects the sharpness of an image, so you’ll need to pay attention to this as well. I usually start with a clarity setting of 25 for my RAW captures and I might bump it up to 50 or so for images with a lot of detail.

There are several other techniques for sharpening photos in Photoshop, including sharpening just the lightness channel in LAB mode and multi-pass sharpening for really big prints. But for most of your images, the above techniques should work great.

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