Sharpen Images With The High Pass Filter In Photoshop
This tutorial shows you how to sharpen images in Photoshop using the High Pass filter. You'll learn how image sharpening works, why the High Pass filter is the perfect tool for sharpening images, and how to combine High Pass with Photoshop's blend modes for amazing sharpening results!
When it's time to sharpen an image, most Photoshop users instinctively turn to either the Smart Sharpen or Unsharp Mask filters, unaware that the High Pass filter, while not technically a sharpening filter, can give us results as good as, or even better than, Photoshop's actual sharpening filters, while at the same time being much easier to use.
Good image sharpening means sharpening the edges around objects without sharpening anything else. What makes the High Pass filter such a powerful tool for sharpening images is that it's able to detect those edges while ignoring areas that are not an edge. We can then combine the results from the High Pass filter with one of Photoshop's blend modes to easily sharpen the edges while leaving the rest of the image untouched. Let's see how it works.
For this tutorial, I'll be using Photoshop CC but everything is fully compatible with Photoshop CS6. To follow along, you can use any image that's in need of some sharpening. I'll use this photo that I downloaded from Adobe Stock:
Let's get started!
How To Sharpen Images With The High Pass Filter
Step 1: Convert The Background Layer Into A Smart Object
When using the High Pass filter to sharpen an image, the best way to work is to apply High Pass as a Smart Filter. This keeps the sharpening effect separate from the image itself and avoids making permanent changes to the original photo. To apply High Pass as a Smart Filter, we first need to convert the Background layer into a Smart Object.
Then choose Convert to Smart Object from the menu:
Photoshop converts the Background layer into a Smart Object and names it "Layer 0":
Step 2: Select The High Pass Filter
To apply the High Pass filter, go up to the Filter menu in the Menu Bar, choose Other, and then choose High Pass. This opens the High Pass dialog box which we'll look at in a moment:
What Is Image Sharpening?
To really understand why the High Pass filter is such a great tool for sharpening images in Photoshop, we first need to understand how image sharpening works. After all, we don't physically sharpen pixels the way we'd sharpen a set of knives. So what does "image sharpening" even mean?
Much like any good magic trick, image sharpening is an illusion. It works by increasing contrast along the edges of objects in an image. Photoshop can't recognize specific objects, of course, so it considers an edge to be any area where there's a big, sudden change in brightness or color between neighboring pixels.
Increasing contrast along the edges makes the light side of the edge lighter and the dark side darker. Your brain then sees the increased contrast as "sharper". The more we boost the edge contrast, the sharper the image looks. But really, image sharpening has nothing to do with "sharpening" pixels. Instead, it's all about increasing edge contrast.
Why Use The High Pass Filter To Sharpen Images?
So if we sharpen images by increasing edge contrast, what does that have to do with Photoshop's High Pass filter? Well, before we can increase contrast along edges, we first need to find those edges, and that's where the High Pass filter comes in. High Pass is an edge-detection filter. It looks specifically for edges in the image and highlights them. Areas that are not an edge are ignored. Once we have the edges highlighted, we can then combine the High Pass filter's results with one of Photoshop's contrast-boosting blend modes (as we'll see a bit later on) to easily increase contrast along edges without affecting the rest of the image.
Step 3: Find The Edges
The High Pass filter's dialog box is very easy to use. There's a preview window at the top and a Radius slider along the bottom. As I mentioned, the High Pass filter detects edges in the image. The Radius value controls how much highlighting to apply to those edges. Any areas that are not an edge are filled with neutral gray.
The easiest way to use High Pass is to start by dragging the Radius slider all the way to the left, to a value of 0.1 pixels (the lowest possible value):
At the lowest setting, the entire image is filled with solid gray, with no edges visible anywhere. That does not mean there are no edges in the image, or that the High Pass filter is not able to detect them. The problem is just that the Radius value is too low at the moment for the edges to be seen:
To bring the edges into view, begin dragging the Radius slider to the right to increase the value. I'll increase mine to 4 pixels:
If we look at the image, and in the preview window in the filter's dialog box, we now see faint highlights around the edges. Here, we see them around the owl's feathers and other features, as well as along the tree branch. Other parts of the image that are not considered part of an edge remain solid gray:
How The Radius Value Works
I mentioned earlier that the Radius value controls the amount of highlighting that's applied to the edges, but that's an oversimplification. What the Radius value actually does is it determines how many pixels on either side of an edge should be considered part of the edge. For example, a Radius value of 1 pixel would mean that Photoshop would include only a single pixel on either side of the edge; one pixel on the light side and one pixel on the dark side. But if we increased the Radius value to, say, 10 pixels, then Photoshop would extend the width of the edges to 10 pixels on either side.
That explains why we couldn't see the edges when we initially lowered the Radius value down to just 0.1 pixels. Photoshop was including only one tenth of one pixel on either side of the edges, making the width too narrow to notice. But when I increased my Radius value to 4 pixels, Photoshop extended the width of the edges out to 4 pixels on either side, making them wide enough to be easily seen.
Pushing The Radius Value Too Far
When using High Pass to sharpen images, be careful not to push the Radius value too far. The reason is because too much of the image will be included as part of an edge. Watch what happens if I increase the Radius value to something extreme, like 40 pixels:
At a Radius of 40 pixels, Photoshop is extending the width of the edges out to 40 pixels on either side, and now pretty much the entire image is considered part of an edge. We've gone from subtle highlighting against an otherwise neutral gray background to a weird embossed effect, with large halos visible everywhere:
Finding The Radius Value Sweet Spot
Remember, sharpening works by increasing contrast along edges without affecting any other areas. So for the best sharpening results with the High Pass filter, choose a Radius value that's just large enough to bring out the highlights while keeping those highlights as close to the actual edges as possible.
The exact Radius value you need will depend on your image. Larger images generally need larger values than smaller images to achieve the same results. In general, Radius values of between 1 and 5 pixels tend to work best. For my image, I'll go with 3 pixels. Click OK to accept your Radius value and close the High Pass dialog box:
At this lower setting, the image is back to being solid gray for the most part. The edge highlighting is visible but subtle. This is the result we're looking for:
Step 4: Change The High Pass Filter's Blend Mode To Overlay
Now that the edges are highlighted, the next step is to increase the edge contrast by blending the High Pass filter's result into the original image. We do that by changing the blend mode of the High Pass filter. In the Layers panel, the High Pass filter is listed as a Smart Filter below "Layer 0". Double-click on the Blending Options icon to the right of the filter's name:
This opens the Blending Options dialog box. The Mode option (short for "Blend Mode") is at the very top. By default, the blend mode is set to Normal. To use our edge highlighting to boost contrast along the edges, we'll need to use one of Photoshop's contrast-boosting blend modes. There's a few of them to choose from, but the one that usually works best for image sharpening is Overlay:
The Overlay blend mode hides any areas of neutral gray, so all of those non-edge solid gray areas created by the High Pass filter instantly disappear from view. It then uses the lighter highlights to lighten the light sides of the edges even further, and the darker highlights to darken the dark sides. This boosts the contrast of the edges and creates the illusion of a sharper image.
Here's a before-and-after comparison to help make the sharpening effect easier to see. On the left is what the original image looked like before any sharpening was applied. On the right is the result using the High Pass filter and the Overlay blend mode:
Trying The Soft Light And Hard Light Blend Modes
If the sharpening effect from the Overlay blend mode is too strong, try the Soft Light blend mode instead. It works exactly the same as Overlay but the results are more subtle:
Or, if the Overlay sharpening effect isn't strong enough, try the Hard Light blend mode. Hard Light will give you the most intense sharpening of the three:
Here's a side-by-side comparison of the High Pass filter set to all three blend modes, with Soft Light on the left, Overlay in the center and Hard Light on the right. The Overlay blend mode is generally the one you'll use the most:
Step 5: Lower The High Pass Filter's Opacity If Needed
Finally, regardless of which blend mode you choose, you can fine-tune the sharpening amount even further by adjusting the opacity of the High Pass filter. You'll find the Opacity option directly below the Mode option. The more you lower the opacity from its default value of 100%, the more the original, unsharpened image will show through. Once you've chosen the blend mode that gives you the right amount of sharpening for your image, and you've adjusted the High Pass filter's opacity if needed, click OK to close the Blending Options dialog box:
Step 6: Toggle The Sharpening On And Off
The easiest way to judge if you've applied the right amount of sharpening to your image is to compare the result with how the image looked before it was sharpened. To view the original, unsharpened version, click the High Pass filter's visibility icon (the eyeball icon) in the Layers panel:
This temporarily hides the sharpening effect, revealing the original image:
Click the visibility icon again to turn the High Pass filter back on and view the sharpened version:
And there we have it! That's how to easily sharpen images with professional results using the High Pass filter in Photoshop! Visit our Photo Retouching section for more image editing tutorials!