Page 58 - Photoshop User February 2017

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Photoshop Proving Ground
how photoshop sharpens your images
Sharpening is really just contrast enhancement along an edge or boundary, so let’s see how Photoshop sharpens your images. In terms of a digital image, an edge is just a difference in brightness and/or color that’s spread over some distance, technically called a “discontinuity.” The distinction between an edge and a gradient is distance relative to the size of features in an image, as well as the image itself. That is, as the width of the edge increases, it tends to become a gradient. It’s a squishy concept but, an important one.
SCOTT VALENTINE
Note: In technical image analysis, an “edge” is a single dis- continuity, but a “boundary” is a collection of connected edges that form an enclosed region of the image. In order to simplify for this article, I’ll use both terms to mean the same thing.
In the example image on the right, the top squares have clear edges, but as we add blur, it becomes more diffi- cult to distinguish between the pure gray values of each box, until the entire image becomes a continuous gradient from white to black. The drawn curves represent the width of each transition. If you had to choose, which set would you say still has edges? Most photographers would say only the top one, but consider that if you can at least make an educated guess about the edges, there’s a chance for some recovery by dramatically, possibly artificially, increasing contrast to reduce the width of the edge. At this point, we now have to consider the concept of “how much.” How much distance and how much contrast
define an edge? This becomes an important question when considering sharpening techniques and values— more on that in a bit.
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