Photoshop Tutorial: High Pass Sharpening

This superior sharpening method gives you excellent detail retention and superb control over the level of sharpness. 

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What you need

To follow through with this tutorial you need at least Photoshop CS. More recent versions of Photoshop may appear a little different (mostly the interface has added features) as this tutorial is originally from 2006, but the techniques here are sound and work quite well across all versions since its publish.

To follow along with this tutorial you will need to download this image: High-Pass-Sharpening.jpg (right-click and choose: Save As).

When should you Sharpen?

Sharpening an image should always be the very last step in the photo retouching process. Sharpening is destructive to the image, and since the level and technique of sharpening used for an image will vary depending on how you will output the photo, you don’t want to have it stuck in your image from early on. Save sharpening for last, and sharpen according to how you will output the final image.

You should also resist saving a flattened sharpened image over your original. Either save a copy, limit the sharpening effect to its own layer, or omit the sharpening and apply it again next time. Once you get the hang of High Pass Sharpening, you will be able to pull it off in under a minute when you need to.

What Sharpen does

Sharpening is the method of increasing the contrast between two objects, usually isolated to the point at where they meet. What this means is that sharpening simply darkens the lines and lightens the areas around them. If the lines are light, sharpening brightens them even more and darkens the areas around them. This makes lines stand out more. When lines stand out more, the photo looks sharp. Take a look at the example below.

Unsharp line

In this example we use just a simple line on a neutral background. Photos can have thousands of lines in a variety of sizes. Consider this example a microscopic view of a line in a photo. This line has not been sharpened.

 

 

Sharpened line

Sharpening increases the brightness to the area surrounding the black line. This allows the black line to stand out better. It looks more defined. The white lines on the sides are thin and do not cover up much detail (grey) in the rest of the image. Back away from your screen to see how this line stands out more than the first. This is a well-sharpened line.

Oversharpening

Too much sharpening will result in an increase in size of the surrounding accents and cause what is known as haloing. You want to avoid this as the halos cover up some of the detail in the image and make the image look too processed. This is over-sharpened.

Why Use High Pass Sharpening

Photoshop already comes with many sharpening filters built in… why use the high-pass method? The Smart Sharpen filter achieves similar results to the High Pass method, but I feel it lacks the control and visual queues that this method allows. Another great benefit to taking the High Pass route, is that you can easily see just the lines in the image that will be sharpened as you are adjusting the settings. This allows you to get a better feel for the effect of the sharpening once you click OK.

How to Use High Pass Sharpening:

Open the image (High-Pass-Sharpening.jpg) and make sure the Layers Palette is visible. Windows shortcut keys are used here. If you use a Mac, just replace the Ctrl key with the Command key.

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  • Open your photo and duplicate the background layer by pressing Ctrl-J.
  • Double click this layer to rename it to “Sharp(1).

This image is well composed, exposed, and the color looks great, but it is a little soft. Sharpening can help improve definition in the details.

Original image Your Layers Palette:
Duplicate layer and rename
  • With the Sharp layer selected, set the Sharp layer’s blending mode to Overlay (2).

The Overlay blending mode will exaggerate tone. When the shadows of one layer are over shadows of the layer below they appear darker. When highlights are over highlights they appear brighter. Since this layer is identical to the layer below, all the shadows darken and the highlights brighten. The contrast of the image is increased.

Overlay layer applied Overlay blending mode
As mentioned above, increasing the contrast between lines and their surroundings is what makes an image look sharp. The Overlay layer we just created, increased the contrast, but across the whole image, not just the lines. So now we have to tell the Sharp layer to only look at the lines. We do this with the High Pass filter. Think of this filter as a “line detection system.” It will eliminate detail in the layer, leaving only the lines, based on the thickness of the line you tell it to detect.
  • With the Sharp layer selected, run the High Pass filter. It’s found under the Filter menu and then under Other.

The Radius setting tells the filter what thickness a line must be in order for the filter to consider it a line. Anything below that thickness will show on the layer. Anything above that thickness will be turned gray.

When choosing a radius value, you want to look in the preview box to see the kind of lines that are being considered.

A lower radius limits the sharping to thinner lines. Higher radius sharpens all lines up to the thicker details.

High Pass filter
  • Make sure the Preview box (3) is checked, so you can see the result of your adjustments immediately on the image below this box.
  • Keep an eye on the Filter Preview (4) and adjust the Radius (5) to the left until you make most of the detail in the filter preview turn grey and all that’s showing are the detail lines you’d like to sharpen.

For this image I found that a Radius of 0.5 worked well to isolate the edges (lines) I want to sharpen.

Basically, at this stage you are choosing which lines to sharpen.

Setting the High Pass filter
The image should now have better defined lines and a crisper appearance.

  • Turn on and off the Sharp layer (using the eye icon in the layers palette) to see the before and after.
  • Change the Opacity of the Sharp layer to increase / decrease the strength of the effect.
High pass-sharpened image

Final Results

When used properly, High Pass Sharpening allows you to pinpoint the type of lines in your photo you want to sharpen, and then control the strength at which they are sharpened. Advanced users can run it on multiple layers, controlling the sharpness of thinner lines on one layer, and then thicker lines on another.

Original

Original

High pass-sharpened image

After High Pass Sharpening

before sharpening

Original (cropped)

High pass sharpening

After High Pass Sharpening

Original image

Original image

After High Pass Sharpening

After High Pass Sharpening

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High Pass Sharpening Tips

  • Larger images may require a higher High Pass radius value.
  • Sharpen defined lines, not small details.
  • Use masking to mask away areas, you do not want sharpened (areas beyond the depth of field).
  • Sharpening works best on images that have corrected tone and colors. Fix those issues with your image first.
  • Save sharpening for last and don’t save a sharpened version over your original.
  • For prints, set the radius based on the viewing distance and size of the print. For prints that will be viewed from a distance, use more sharpening than normal. Larger prints may show this exaggerated sharpness so find a balance between viewing distance and print size. The larger the viewing distance, the more sharpening. The larger the print size, the less exaggerated sharpening is needed.
  • Don’t limit yourself to using sharpening once. Sharpen once for one radius of lines, then again for a different radius.
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