One of the most critical processes for working with digital photos is how to sharpen them. Most compact cameras use quite heavy sharpening by default but often allow the user to tone it down a bit. Obviously, in the case of a DSLR, the option to remove sharpening completely is usually available. In the case of shooting RAW, no sharpening should be present at all. It goes without saying that sharpening in post-processing is a lot more effective than what a camera’s processor can do in a few milliseconds. One of the most effective methods of sharpening is the Darken/Lighten technique.
The idea behind the technique is that we sharpen those parts of the image that will yield the clearest sharpening results. The name comes from the fact that we create a layer for dark edges and another for light edges. Its advantage over using Unsharp Mask alone is the fine-grained control it gives you together with more detailed results.
So, let’s work on our image.
It should be pointed out that the parameters used are for a medium-sized image of 1280×853, sized down from an 8Mpixel Canon 20D RAW image. The values will need to be adjusted depending on the original image. More about this later…
The first thing to do, once you have your image open, is duplicate the background layer. This is a completely non-destructive process, which is one of its strengths.
Let’s name this layer “darken”:
so we end up with 2 identical layers:
Now we come to the actual sharpening. Find Unsharp Mask in the Filters menu:
And give it some quite severe values as seen here:
The Radius parameter is the one we need to keep an eye depending on the size of the image we’re working on, and what our output target is going to be. For example, for a full-size 20D image that will be printed, the Radius will typically be upped to a value between 1 and 1.5. Later we’ll see what else we can do to increase the intensity of the effect.
Next we need to decrease the Opacity of the layer, to let our untouched original to show through. Pick 60% for now:
and this is where the Darkening come in. Change the blending mode for the sharpened layer to “Darken”.
The effect should now appear much more subtle!
We now want to duplicate this darken layer to make our lighten layer. Do the same as when duplicating the background in the first place renaming the layer to “lighten”, so that we end up with 3 layers:
We’re going to want this image to pick out lighter details, so change its blending mode to “Lighten”:
Usually, it’s a good idea to have this layer less opaque then the darken layer, or the effect can be quite strong. Let’s use 30% as a starting point:
Now, take a look at the results. The effect is to bring out details, all the time leaving our original layer as it was. This is the beauty of non-destructive editing. Of course, the downside is that we’re storing 3 times as much data. But, well, diskspace is cheap! Here’s a before-and-after look at a boring sample image:
The real power of this technique is that the 2 sharpening layers can be adjusted very quickly by altering their opacity. This is especially quick using the keyboard shortcuts (1 for 10%, 2 for 20%, and so on up to 0 for 100%). For speed, I’d recommend putting all this into an Action, so you can launch it with default values with one swift keyboard shortcut.