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Photography

Quick, Best, Selective: 3 Image Sharpening Techniques for Every Situation

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This post is part of a series called How to Sharpen Digital Images.
Selective Sharpening Using High Pass in Adobe Photoshop
Unlikely Friends: Grain, Noise, and Sharpening

In the last two tutorials in this series we looked at what sharpening is and the hidden problems you’ll encounter. Now it’s time to get into the technical side of things. In this tutorial we’ll look at some of the different methods for sharpening and when they are best used. So let’s dig in.

Why We Don’t Use Sharpen, Sharpen More and Sharpen Edges

In Adobe Photoshop’s Sharpen menu, you’ll notice four filters that I’m ignoring in this series: Shake Reduction, Sharpen, Sharpen More and Sharpen Edges. Let’s look at why.

Shake Reduction is a powerful filter with a very specific use: removing blur from camera shake. We might dive into it in a later tutorial but it has no role in general sharpening. In my opinion, however, the best way to avoid camera blur is to use an appropriate shutter speed rather than to rely on Photoshop.

shake reduction
Shake Reduction is a great filter but has no place in a sharpening workflow.

The Sharpen filter is also the basis for Sharpen More and Sharpen Edges. All three are legacy filters that Adobe recommends you don’t use. They apply an automatic amount of sharpening to the image. You have no control. Sharpen applies a small amount, Sharpen More is the same but stronger and Sharpen Edges focuses on edges while ignoring other areas. These filters have no place in a good post-processing workflow.

Instead, let’s look at the filters you should be using.

Unsharp Mask: Quick and Simple

In the first tutorial in this series we had a quick look at the Unsharp Mask filter but let’s recap. Unsharp Masking is a film technique where a blurred copy is subtracted from the original image; this creates an “unsharp mask” of the edges. The mask is then used to increase contrast at these edges. 

You can roughly mimic the effect yourself in Photoshop by:

  • Converting the image to black and white.
  • Duplicating the original image.
  • Applying a small Gaussian Blur.
  • Changing the layer blend mode to Subtract. This will create an unsharp mask of the edges.
  • Create a new layer and Merge Visible to it. 
  • Change the layer blend mode to Screen and turn off the unsharp mask layer.
  • The original file will now appear (pretty badly) sharpened.
unsharp demo
The unsharp mask process described above.

In that tutorial I walked you through the mechanics of applying the Unsharp Mask filter in Photoshop; it does a much better job at sharpening images than the hacked together solution above. Rather than repeat the same steps, let’s look at when the Unsharp Mask filter should be used.

The Unsharp Mask filter is the simplest controllable method of sharpening your images. It’s not the best, but it’s quick and easy to use. For images that only need a small amount of general sharpening—and aren’t at risk of any of the problems I highlighted in the previous tutorial—it’s a very convenient way to apply it.

sharpened with unsharp
I sharpened this image for the tutorial with the Unsharp Mask filter.

Smart Sharpen, which we’ll get to next, uses the same general principles as Unsharp Mask. Unless you need to use its extra features, then the Unsharp Mask filter is the best choice.

After I do all my sharpening on the full resolution master file—normally with Smart Sharpen and the High Pass technique which we’ll also cover—I resize a copy of the file to the size I want to export it at. I’ll then use Unsharp Mask to apply any extra sharpening the export copy needs. Images that have been resized down to web size, for example, lose a small amount of definition. A conservative application of Unsharp Mask is a fast and appropriate way to sharpen these images.

Smart Sharpen: The Best General Option

Smart Sharpen is Photoshop’s best overall sharpening filter. With it, you have the most control over how sharpening is applied to the whole image. In the tutorial on sharpening problems, I mentioned that sharpening is best when used on the midtones. To do this, you need to use Smart Sharpen.

To apply the Smart Sharpen filter, create a new layer (Shift-Command-N and Merge Visible to it. You’re now working on a copy of the original image and all the adjustments you’ve made.

Go to Filter > Sharpen > Smart Sharpen… If the Advanced Options aren’t visible, click on Shadows/Highlights to reveal them.

smart sharpen
The Smart Sharpen dialogue box.

The options here are a little different so let’s look at what they do:

  • Amount and Radius are the same as Unsharp Mask. They control how strong the effect is and what size of details it affects.
  • Instead of Threshold, Reduce Noise is used to prevent over-sharpening noise. The higher the percentage, the more selectively the sharpening is applied. Values that are too high can make the whole photo look plasticky. 
  • Remove has three options: Gaussian Blur, Lens Blur and Motion Blur. Gaussian Blur is the best option for most uses. If you’re trying to remove blur from a camera movement or a subject movement, Lens or Motion may be appropriate.
  • Fade Amount controls how sharpening is applied to the shadows and highlights. A value of 0% means they are sharpened the same as other areas of the image. A value of 100% means they aren’t sharpened at all.
  • Tonal Width determines what areas are considered shadows and highlights. A smaller amount means that only the darkest or brightest areas of the image are affected.
  • Radius is used to control how pixels adjacent to shadow or highlight areas are affected. Any pixel that lies within the radius value of a shadow or highlight pixel will also be considered a shadow or highlight. This prevents over-sharpening of small colour variations.

To use Smart Sharpen, start at the top of the dialogue box and work down. Like with Unsharp Mask, enter an Amount of between 100% and 200% and then slowly increase the radius until you’re happy with how the sharpening affects the midtones. For now, ignore the shadow and highlight areas.

Unless noise is an issue in the midtones, set Reduce Noise to a low value. I often use 0%. For most images, leave Remove set to Gaussian Blur

Look at the shadow areas of your image. These areas frequently have the biggest noise issues. If the sharpening is creating some problems, increase the Fade Amount until they go away. 

Depending on the image, you can also use Tonal Width to determine what Photoshop considers a shadow. If you only have issues in the darkest areas, lower the value. Otherwise, I’ve found somewhere around 50% usually works well. 

Look at the areas where shadows border midtones and highlights. Play with the Radius slider until the transitions look good and not sharpened too little or too much. 

Finally, repeat the process for the highlights. Click OK and you’re done.

If the sharpening looks too intense, you can lower the Opacity of the layer. This is actually a great way to work: instead of spending a lot of time tweaking every slider in the dialogue box, err on the side of slightly over-sharpening your image. It's much easier and faster to simply reduce the Opacity of the sharpening layer on an over-sharpened image than it is to have go back into the dialogue and rework and image that is undersharpened.

unsharp vs smart
The image on the left was sharpen with Unsharp Mask, the middle image with Smart Sharpen and the right image is the differences between them. You can see that in there are more differences in the shadows and highlights where I've deliberately not sharpened details.

Smart Sharpen should be your go to sharpening method for general sharpening. With it, you get total control over how sharpening affects the shadows, midtones and highlights.

High Pass: Selective Sharpening

The Unsharp Mask and Smart Sharpen filters are great for overall sharpening but they’re more limited when it comes to sharpening specific areas of an image, such as a model’s eye. Being able to sharpen certain features while not affecting others is one of the most important parts of creative sharpening.

local sharpening with a High Pass layer
I used three different High Pass layers to sharpen various areas of this image. 

My favourite tool for doing this is using High Pass layers. You’ll find them under Filters > Others. They create an unsharp mask without applying it. This means you can see exactly what edges it’s affecting and mask it in to the parts of the image you want to apply it to.

Selective Sharpening with High Pass layers is something Dawn Oosterhoff has already covered here on Tuts+. She’s written an amazingly detailed tutorial on the process so I’m not going to repeat her work. Check out her article for more information on local sharpening.

Wrapping Up

With the Unsharp Mask, Smart Sharpen and High Pass filters all your sharpening needs are met. Regardless of why you need to sharpen an image, one of these tools will fit the job. There are other, more advanced, sharpening techniques out there but unless you’re a high-end retoucher, you won’t see any benefit from them.

In the next tutorial we’re going to look at why, when it comes to sharpening, noise isn’t always a bad thing. Noise has a surprising influence on how we perceive sharpness. You'll learn how to use noise to your advantage to make sharp, natural-looking digital images.

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