Photoshop Image Sharpening Options
There are lots of ways to sharpen an image in Photoshop. You’ll find some in the Filter menu but there are many other less obvious techniques to use like High Pass Sharpening. In this tutorial, we’re going to look at the Photoshop Sharpen menu to better understand the various options.
You’ll learn about:
- How image sharpening works.
- The menu options to ignore and why.
- A simple way to use the Smart Sharpen filter.
Before you can use these effectively though you need to understand how sharpening works.
How Image Sharpening Works
Sharpening works by enhancing the edges in an image to make them appear clearer. Photoshop does this by comparing adjacent pixels in an image to determine their difference in brightness or contrast. If it finds enough of a difference it detects there’s an edge which it sharpens. Let’s look at a simple example.
Here you can see a simple sharpening edge created from two gradients running from black to white but in opposite directions. Notice at either end you can clearly see the edge between the two gradients. That’s because there is a large difference in contrast between the adjacent pixels. Compare this now to the area in the centre where the line is harder to see. That’s because there isn’t a large difference in the brightness of the pixels.
When Photoshop identifies an edge, it sharpens that edge by increasing the contrast in the adjacent pixels. This means dark pixels become darker and light pixels become lighter. If you’re using a sharpening filter in Photoshop that has a strength or amount slider, that’s what it’s controlling. As you increase the strength of the sharpening you increase the contrast difference between the adjacent pixels. To see this more clearly, look at the following example of the sharpening wedge.
Here we’ve applied sharpening to make the edge between the two strips clearer. If you look closely in the ringed areas, you can even see a faint line along the edge. This edge is the Sharpening Halo and you can usually control its width, often using a Radius adjustment. This controls how wide a halo the sharpening effect uses and therefore how obvious it is. You can see a wide halo in the following screenshot caused by using a large Radius setting.
One final adjustment that you’ll find when using a Photoshop sharpening filter is something called Threshold. This controls how sensitive Photoshop is when checking for edges. When the threshold is low there doesn’t need to be a large difference between two adjacent pixels for Photoshop to detect an edge. But if you increase the threshold, Photoshop needs to detect a large difference between the pixels.
Here’s an example where the Threshold is set to a large value.
And the next example uses the same setting but with a small Threshold setting.
Notice the difference between the two although it’s only the Threshold setting that’s been changed. A Threshold setting, therefore, gives us a way to avoid sharpening any noise on our image and focus our adjustments on the edges.
Now we know the theory of Photoshop image sharpening, watch the video.
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The Photoshop Sharpen Menu
You’ll find the Sharpen menu in Photoshop under the Filter menu and is the first introduction to image sharpening for most people. Although the menu has seen some changes in recent years, it can still be misleading. You can see a screenshot of the Photoshop Sharpen menu below.
The options are:
- Shake Reduction is a recent addition to Photoshop. It deals with the challenge of trying to correct the problem of camera shake. This is usually the result of poor technique or using a shutter speed that’s too slow. Shake Reduction is a large topic and better dealt with in its own tutorial.
- Sharpen applies limited strength sharpening to an image. Often this is enough for an image that’s already in focus but unfortunately, it doesn’t offer any control over the settings.
- Sharpen Edges is a special form of sharpening which concentrates sharpening onto the edges in an image. Landscape images often benefit from this type of sharpening as it concentrates the effect onto the detail in the image. At the same time, it can help to avoid sharpening areas like the sky. As with the Sharpen menu command, you don’t have any control over the settings used.
- Sharpen More is very similar to the Sharpen option except the effect is stronger. It may even be too strong for some images.
- Smart Sharpening is a relatively advanced method of sharpening that often produces excellent results. As well as offering the standard sharpening sliders it has many other controls to improve your results.
- Unsharp Mask is one of the earliest methods of image sharpening in Photoshop and is still very effective. It gets its name from the sharpening technique used in the days of the darkroom. Although it may be “inferior” to Smart Sharpening, you would be hard pressed to see any difference between the two for many images. The Unsharp Mask also has the benefit of being quicker to use and easier to understand.
Let’s now look at which of these options to use and why.
Which Option to Use and Why
First, if you’re not trying to remove camera shake from your photo, don’t use the Shake Reduction filter.
Secondly, you should discount using the three menu options Sharpen, Sharpen More and Edge Sharpening. Whilst these options can improve the appearance of sharpness in your images, you can’t control the effect. In almost every case you will be able to improve your results by using either Smart Sharpening or the Unsharp Mask.
If you would like to use the edge sharpening technique, I explain how to use Photoshop to do this here. You can then apply this technique with either the Smart Sharpen or Unsharp Mask filters.
To sharpen an image well using one of the Photoshop Sharpen menu options, you should be using either Smart Sharpening or the Unsharp Mask. As I’ve already mentioned, for most general images you won’t detect a difference in results between the two. Use the filter you feel most comfortable with.
To find out how to use the Unsharp Mask in Photoshop please see this tutorial.
Quick Guide to the Smart Sharpen Filter
If you’re opting to use the Smart Sharpen Filter, the following should help you understand the main options. You can see a screenshot of the filter dialog below.
On the left of the dialog, you can see a preview of a small area of the image. You can use this to select an area that you want to monitor closely whilst sharpening. At the same time, you can see the effect of the sharpening on the overall image using the “Preview” tick box.
A further benefit of the Smart Sharpen filter over the Unsharp Mask is you can create and save Presets. This allows you to quickly apply settings you know have worked well in the past. If you’re unsure about some of the options in the dialog, the Default preset is a good place to start. This adjusts the visible settings and disables the more advanced “Shadows / Highlights” controls.
The Amount adjustment controls the strength of the sharpening effect. When you use a higher value, the effect becomes stronger but watch out for halos becoming visible.
It’s also possible to control halos with the Radius slider. The default for the Radius is 1 but as you increase this the effect becomes easier to see as the sharpening halo becomes visible. If you make the Radius too wide the halo becomes obvious and the image appears over sharpened.
The Reduce Noise slider helps prevent you sharpening any image noise that’s present. If you sharpen noise it makes it more obvious. In the Unsharp Mask filter, you can achieve this using the Threshold slider. It’s likely the Reduce Noise option is doing something similar but none of the documentation I can find is clear.
The Remove dropdown towards the bottom controls the type of sharpening you’re applying and has three options. The Default is Lens Blur which tends to favour sharpening edges and finer detail. This can also help to control the sharpening halos becoming visible and is a good option if you’re sharpening a landscape image. The Gaussian Blur sharpening is stronger than the Lens Blur. It’s also the same method as used in the Unsharp Mask filter.
The final option is Motion Blur and tries to remove blurring introduced by movement. If you find you need to use this option because of camera shake, consider using the Shake Reduction… filter discussed earlier.
As this is a simple introduction to the Smart Sharpen filter, we won’t be covering the Shadows / Highlight options. To learn about these features see Mastering the Photoshop Smart Sharpen tutorial.
In this tutorial, we’ve covered how sharpening works what the various menu options do and how which to choose when sharpening an image. If you decide to use the Smart Sharpen filter you should be able to understand the main controls which will allow you to produce good results. If instead, you choose to use the Unsharp Mask filter the controls should also make sense to you based on the discussion of how sharpening works.
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