Join Deke McClelland for an in-depth discussion in this video Sharpening and gradual transitions, part of Photoshop CS4: Sharpening Images New Features.
In this exercise, I am going to show you what happens to those dark and light halos that are produced by Photoshop Sharpening Filters, when we are working with an image that contains gradual transitions. I still have open sharpshapes.psd found inside the how_it_works folder. I've got my Layer Comps palette open. I'm looking at the Standard version, the original version of this image. I am going to switch over here to Gradients. And what we now have is a gradient version of this image. So in other words, we've got a dark to light serpentine line here, this thick serpentine line, against a light to dark background.
So there is a point at which, right here in the middle, where things start to get awfully similar. And we are starting to lose the steepness of the edge. And again, when I say steepness of the edge, imagine that light is very high, like a mountain, and dark is very low, and then right at that point between the two you have a ginormous cliff right there. And of course, the job of sharpness is to create these halos that elevate or carve into that cliff, so that we're increasing the size of that cliff at that location.
So let's take a look at what that means. Let's go ahead and zoom in, actually at the top of the image for a moment here. And then I'll show you what these gradients would look like if they were sharp. So when we sharpen the gradients, we get this effect here. So Photoshop has gone ahead and drawn a dark halo on the dark side of this edge, and a light halo on the light side of the edge. And notice as we scroll down here, that the halo grows thinner and thinner and thinner and just sort of drifts away. As you can see, it's almost like a calligraphic line that you're drawing with a pressure sensitive stylus.
And we're letting go off the stylus and the line is getting thinner and thinner as we get to this area of midtones, where we really don't have an edge anymore. There's not much of an edge for Photoshop to lock onto. So the dark edge goes away. The dark halo starts going away. It tapers off. The light halo tapers off as well and then what happens is they switch places. Notice that, now we're having a tapering white halo on the inside edge, on the light edge still, and a tapering dark line, dark halo here, on the dark edge still.
So again, Photoshop is smart enough to elevate the contrast according to whether it's finding a dark edge or a light edge inside of the image. And then the line grows nice and thick and stays as thick as it's going to be anyway, and that's something you can control. You can make ultra thick halos or very, very thin halos and these are pretty thin halos actually. But notice that it's growing darker, and darker, and darker, as we descend toward the bottom portion of the image. So again, where Photoshop has something to lock onto, that's where it's going to sharpen those details.
Where it can't find anything, it's not going to produce any Sharpening effect. So as a result, if we zoom out from this image to take in more of the image at a time, we can see a lot of sharpness up here at the top. We can see a lot of sharpness down here at the bottom. We're not seeing much sharpness, not nearly as much sharpness here in the middle of the image, because there wasn't enough contrast in the first place to pull it off. So, just for the sake of comparison, this is the before version of the image, and this is the after version. Where edges occur inside the image, they appear to be edgier than ever.
In the next exercise, I am going to show you the effects of combining Sharpening with Noise Removal.