Posted by: David Vernon | May 28, 2009

Photoshop Friend #3 – Sharpening

Mackinaw River East from TowerlineSharpening is one of those often mentioned, frequently heard terms tossed about in Photoshop. Yet a lot of newcomers to post-processing aren’t entirely sure what it is.

So what is it?

Sharpening is simply a process that does exactly what the name implies – it actually makes an image look sharper or crisper. Having said that however, it’s important to understand what sharpening cannot do. It can’t take an out-of-focus image and make it look okay. Out-of-focus is just that – and will ever remain that. Sharpening is best for taking a good image – that’s somewhat sharp to begin with – and making it even more distinct.

Now – how does this happen? Think of sharpening as local contrast enhancement. In fact contrast enhancement along edges – between areas of contrasting light and dark. These areas are played up and increased – and the resulting effect is one of even more obvious edges.

Perhaps one moment of confusion is in the most common name for the sharpening process – the Unsharp Mask – doesn’t help clarity. But there’s a very good reason for this name. Back in the day, if you wanted to sharpen in the darkroom, you used a slightly blurred and inverted version of your image (if you were printing from a negative, you used a slide and vice versa) to achieve the effect. So you were masking your original image with something that was unsharp to play up areas of contrast. And hence the name Unsharp Mask was born.

The process in post is pretty easy – but there are a few golden rules to apply. Sharpening should always be done last. If you do it in the middle of the process, subsequent edits can either exaggerate or do away with your results. Secondly, you should always sharpen on its own layer (and set the blend mode to Luminosity). This let’s you lower the opacity to decrease the effect. Next, I like to zoom into 100% when I sharpen. The results are a lot more obvious at that zoom and you can decide much easier how much you want. Finally, I always tend to sharpen on either a flattened image or I merge everything up to a new layer so my effect is on the whole image.

Beginning with Photoshop CS3, the new term of “Smart Sharpening” was introduced. That tends to be how I sharpen nowadays, but the Unsharp Mask is similar – and still very effective – and we’ll focus on that. If you want to “Smart Sharpen”, I recommend working on an amount around 100% and a radius of one. I like to remove “Lens Blur”.

Let’s look at the Unsharp Mask on yet one more Irish image – some stonework in a Dingle garden:

Sharp01First of all, you’ll notice that the preview is already at 100%. Toggle the checkbox on and off to see the effect. Sharpening has three settings – Amount, Radius, and Threshold. Let’s talk about each one:

Amount – This is the value of the contrast. A higher number means increased contrast and a more “smack-you-over-the-head” sharp look. In the case of sharpening an image, too much sharpening is not a good thing. And like certain other things in our world, you’ll know too much sharpening when you see it.

Radius – This is the size of the sharpening contrast enhancers – usually little halos that are drawn in the contrasty areas. The smaller the radius, the smaller the halo. You don’t need much.

Threshold – This is your edge determination tool. The higher the number, the more discernable an edge that is required to qualify for sharpening. A real small threshold can actually add noise in those areas, so it’s best to stay at or above five.

Once you understand those three variables, the remaining determination is are you sharpening for “print” or for the “web”.

  • Print – For standard sharpening start with Amount = 100, Radius <= 2, and Threshold = 5
  • Print – For soft images, increase Amount = 140, decrease Radius <= 1, and raise Threshold = 10
  • Web – For standard sharpening for the web go with Amount = 200-400, Radius <= 0.5, and Threshold = 0.

Obviously your output makes a big difference in the path you choose. If you’re doing both I suggest saving two images with different levels of sharpening. Also, consider these starting points – look at the image – both at 100% and at a more normal size – and see what you think.

If you are predominantly sharpening a person, err on the low side. A general recommendation is to not exceed your Print Standard criteria, and in fact to go a little lower on all categories.

Let’s look at a before and after on our Irish image, again set to 100, 1.5, 5:



The main difference between the two images occurs on the edges – the letters, the greenery in front of the stonework, where the stonework interacts with the wall.

You want the effects to be subtle. I always tend to oversharpen a little and then pull it back with a lowered layer opacity. Take a look at the third image in the sequence. That’s sharpness overkill.

Amount = 100, Radius = 1.5, Threshold = 5, Layer Opacity = 50%

Just Right: Amount = 100, Radius = 1.5, Threshold = 5, Layer Opacity = 50%

Amount = 150, Radius = 5, Threshold = 3, Layer Opacity = 100%

Too Much: Amount = 150, Radius = 5, Threshold = 3, Layer Opacity = 100%

In the end, keep it understated and things will really pop when you put the image on paper.

Okay – now you have three certified Photoshop post-processing tricks up your sleeve that can really improve your image. These three alone will carry you for awhile – we’ll take a little time off and come back with a few next steps…

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