Sharpening De-Mystified

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The Honda Tent and Pagoda at the Indianapolis Motor Speedway

We all want absolutely tack-sharp photos. We all know that sharpness begins with the shot itself – there is no saving a blurry photo in post-production. We are somewhat familiar with sharpening techniques in Lightroom or Photoshop, but what is the best way to apply sharpening for landscapes? Portraits? Cars? Street scenes? When is the best time to sharpen? Is there a difference between sharpening for viewing on-line and sharpening for printing? What do the terms “amount” and “radius” and “threshold” mean?

Let’s begin to de-mystify the process of sharpening!

Two Rules of Thumb

The first rule of thumb is to apply sharpening as the very last step in the post-processing workflow. This is because softening can result from various editing techniques, so you want to sharpen the photo after all of the editing has been completed. The second rule of thumb is to view the photo at a magnified level (like 50%) as you sharpen, so you can really tell how the sharpening levels are affecting the image.

How Does It Know?

Post processing software such as Photoshop CS5, Lightroom 3, and Aperture 3 determine the where the edge lines are in the photograph by looking at the demarcation between lines of light pixels and lines of dark pixels. Depending on the settings that you use, sharpening is achieved by lightening the pixels next to the light lines, and darkening the pixels next to the dark lines. This creates greater definition along the edges of the subjects and details in the photograph, which translate into a sharper images as seen by our eyes.

This is a great exaggeration, but shows what I’m referring to. The first image is not sharpened at all, zoomed in to 1200% so you can see individual pixels:

This is an example with an extreme amount of sharpening added. Note the layers of contrast between the red and blue that the program added (click to see full-sized pixels):

What Do Those Unsharp Mask Settings Mean?

Amount: This refers to how significantly you want to sharpen the image. The higher the number you use, the more exaggerated the edges become. The light lines added next to the light edges become even lighter, and the dark lines added next to the dark edges become even darker. In the exaggerated photo of sharpening above, I set the Amount to 200%. This is what it looks like at 50% – notice the added blue lines aren’t AS blue, and the added red lines aren’t AS red (click to see full-sized pixels):

Radius: This effects how many pixels away from the identified edges the sharpening will be applied. A lower radius number means the changes will stick closer to the identified edge line, and a higher radius number means the changes will spread out further from the identified edge line. In the exaggerated photo of sharpening I applied a Radius of 5.0. This is what it looks like at 1.0 (click to see full-sized pixels):

Threshold: Threshold defines what the program considers an “edge” and what it does not. A high threshold number tells the program that a pixel needs to be very significantly different than surrounding pixels in order to be considered an “edge”. A low threshold number tells the program that only minor differences in pixels should define an edge. In the exaggerated photo I used, I set the threshold to “1″ – this means that more content within the photo will be sharpened because there are more incidents of slightly differing relational pixels than greatly differing relational pixels. In this example I set the threshold to “50″ (click to see full-sized pixels):

What Settings Should I Use?

Flowers and other “soft” subjects: You’ll want a fairly high amount (around 130-150%) with a very low radius (1 or 2) and a moderate threshold (8-12).

Portraits: You don’t want to overly-sharpen a portrait, but you do want to make things like eyes and hair highlights stand out. Try an amount of 75-100%, a radius of 2 or 3, and a threshold of 3-5.

Landscapes: There tend to be lots of edges and details in a landscape photo, so it’s appropriate to boost up the sharpening. Try an amount of 110-125%, a radius of 1, and a threshold of 3 or 4.

Very detailed (buildings, cars, anything intricate): If you want to sharpen the HECK out of your photo, set the amount to 60%, the radius to 5 and the threshold to 1.

Scott Kelby’s “All Purpose Sharpening”: In Scott Kelby’s book The Adobe Photoshop CS5 Book for Digital Photographers , Kelby mentions that his favorite “all purpose” sharpening settings are amount 85%, radius of 1, threshold of 4. I do find this to be just the right amount of sharpening for most of my photography.

Sharpening for printing: If it looks just a little bit TOO over-sharpened on the screen, chances are it’s going to look just right when printed. Print out a few test prints on your printer until you establish how much sharpening results in the best prints.

In the shot at the beginning of this entry (taken at this summer’s MotoGP race in Indianapolis – the red Honda tents are in the foreground, and the track’s Pagoda is in the background), which was used for each example, I finally settled on an amount of 85%, radius of 1, and threshold of 3.

Photo credit: Tiffany Joyce

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