How to Sharpen an Image in Photoshop Using a High Pass Filter
Have you ever had a photo that was a little soft, leaving you wondering how to sharpen an image in Photoshop?
You aren't alone, my friend...
Many of my photography colleagues use Photoshop's Smart Sharpen feature or the Unsharp Mask to sharpen up their photos. However, I like a different approach.
In this post-processing tutorial, I'll show you how to sharpen an image in Photoshop using a High Pass Filter.
How to Sharpen an Image in Photoshop: How Sharpening Works
Photo by kurmyshov via iStock
Make no mistake - your goal should be to get your images perfectly sharp in-camera. Doing so results in a better result and spares you the time and effort to sharpen the image in Photoshop.
Besides, sharpening an image in Photoshop doesn't technically sharpen anything. Instead, it's an optical illusion that makes the image appear sharper.
This is done by boosting the contrast in the image, in particular, along the edges of the features in the shot.
Doing so makes the highlighted edges lighter and the shadowed edges darker. Our eyes then see those edges as being sharper. See what I mean in the video below by Tyrone John:
What makes the High Pass Filter such a good sharpening tool in Photoshop is that it is specifically designed to look for edges. Since those edges are where we need to work, that makes it an ideal tool to use for sharpening.
Essentially, the High Pass filter scours the shot for edges and highlights them. Anything that isn't an edge is passed over and ignored.
Once the High Pass Filter has done its thing, you can use any number of Photoshop's blending modes that increase contrast to work on all those edges.
Pretty simple, right?
Below, I've got a step-by-step process for how to use a High Pass Filter to sharpen your photos, which, in my opinion, is the best way to sharpen images in Photoshop.
How to Sharpen an Image Using a High Pass Filter
To illustrate this process, I'll use a photo I recently took on a trip to the Lofoten Islands in Norway.
You can follow along and complete each step using any photo of yours that needs sharpening as well.
How to Use a High Pass Filter Step 1: Convert Background Layer to Smart Object
Begin the process by converting the background layer into a smart object. Doing so enables you to use the High Pass Filter as a smart filter, which is non-destructive.
In looking at the Layers Panel above, you'll see your image on the background layer.
Converting the layer to a smart object is as easy as clicking the Menu Icon (shown above) in the top-right corner of the panel and choosing Convert to Smart Object (shown below).
Once you've done so, a smart object icon will appear in the lower-right corner of the thumbnail preview:
This indicates that we can work on the image using a smart filter and leave the original image untouched.
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How to Use a High Pass Filter Step 2: Select the High Pass Filter & Adjust the Radius
The next task is to select the High Pass Filter. You can do so by selecting the Filter Menu > Other > High Pass, as shown above.
As you can see below, doing so turns the image a neutral gray.
At this point, the High Pass filter looks for all the edges in the shot. Once it identifies those edges, the filter highlights them.
The Radius value indicates the width of the highlighted edges (in pixels) in the photo.
So, if you set the Radius Value to 8.2, as was done above, the High Pass Filter will highlight 8.2 pixels on either side of the edge.
Now it's time to adjust the Radius using the slider control.
How to Find Radius
As you can see below, selecting a Radius Value of 0.1 results in no edges showing in the shot.
You can see how moving the Radius slider to the right brings out the edges in my photo:
This is how to find Radius in the High Pass Filter - the more you increase the radius, the more distinct the edges in the shot become:
I've found that the simplest method for getting the ideal Radius Value is to start the slider at its minimum - 0.1 pixels - and slowing dragging the slider to the right.
Of course, as you can see above and below, too much Radius is not a good thing...
The more you increase the Radius Value, the more of the image that will be highlighted. In other words, if the Radius Value is too large, you'll begin to lose the distinct edges as more and more of the photo will be sharpened.
I've found that when it comes to how to find Radius for each image, less is more.
You just want enough of a Radius Value to get those edges highlighted while avoiding having too much real estate in the shot included in those highlights.
As you can see above, I've selected a Radius of 2.4 pixels for this shot.
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How to Use a High Pass Filter Step 3: Close the High Pass Filter
Once you've found the ideal Radius Value, click OK to close the High Pass Filter.
After you close the High Pass Filter, you will see it indicated as a smart filter below the image thumbnail, as shown above.
How to Use a High Pass Filter Step 4: Change the Blend Mode to Sharpen the Image
Now that the edges in the photo are highlighted, it's time to sharpen the shot by changing the blend mode in the High Pass Filter.
If you double-click the Blending Options icon (shown above), you'll be presented with the various blending modes for the filter.
Below, you can see the Blending Options box. Overlay is currently selected, though you can also use Soft Light, Hard Light, or Linear Light for sharpening purposes.
Each of the four contrast blend modes works in a similar way - they hide the neutral gray areas of the shot (everything that isn't an edge).
Since those areas are no longer visible, sharpening will not impact them at all.
High Pass Filter in Overlay Mode
Above, you can see the results of using the Overlay mode.
Overlay is perhaps the most popular blending mode because it produces a high-contrast effect. As a result, the High Pass Filter can see the edges more clearly and apply sharpening more effectively.
High Pass Filter in Soft Light Mode
The Soft Light mode, on the other hand, results in lower contrast. This means sharpening that is more delicate, though it is still noticeable (shown above).
High Pass Filter in Hard Light Mode
The remaining two blending modes result in even more contrast and sharpening than Overlay Mode.
Above, I've used Hard Light mode for sharpening. Below, I've used Linear Light.
High Pass Filter in Linear Light Mode
The Linear Light mode is, by far, the strongest mode for sharpening.
As you can see above, it's way too sharp and has an unnatural, over-processed look.
For my liking, the Overlay mode is the best, though you can tone down the sharpening of the other filters by adjusting the opacity.
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How to Use a High Pass Filter Step 5: Adjust the Opacity
After you've experimented with the blend modes and found the one that best suits your photo, you can make further adjustments to the amount of sharpening by changing the Opacity.
As you lower the Opacity, the sharpening will reduce. Conversely, increasing the Opacity increases the sharpening.
How to Use a High Pass Filter Step 6: Close Out the Filter
Now that we've applied the filter, adjusted the Radius, selected the Blend Mode, and adjusted the Opacity, it's time to close out the filter by pressing OK.
To see how the sharpened image compares to the original, just press the Visibility Icon to toggle the High Pass Smart Filter on and off.
So, in just six steps, you can add sharpness to your image and rescue photos that, apart from a little softness are on point.
Above, you can see my final image.
Again, as I noted earlier, less is usually more, so I have been very judicious with the sharpening of this shot.
This is often a matter of personal preference, though, so experiment with the High Pass Filter and find what works best for you. Regardless of the Radius, Blend Mode, and Opacity you use, you now know how to sharpen an image in Photoshop!
