Sharpening with the High Pass Filter in Photoshop

The high pass filter allows you to sharpen the image in a non-destructive way.

Sarang Naik takes you through the step-by-step process of sharpening your images with the high pass filter in Photoshop CS5.

The anti-aliasing filter in front of the camera’s sensor tends to slightly soften the image. This  makes sharpening an essential part of digital post processing, especially with RAW image files with the in-camera sharpening turned off. Sharpening should ideally be the last step in your workflow to avoid problems like halos which are caused by high contrast.

There are many filters in Photoshop to sharpen an image, the most popular being Smart Sharpen and Unsharp Mask. However, one powerful and easy tool that is often ignored is the high pass filter. But how is it different from all the other tools in Photoshop and Lightroom? Well firstly, it accentuates the high contrast areas and edge details to make them appear sharper. Secondly, you add the effect on a separate layer, so you don’t destroy the original image. Thirdly, it is much simpler to use, with only one slider to set the radius. It is easy, effective and non-destructive.

So let’s see how to use this filter in five simple steps. I have used Photoshop CS5 for this tutorial but it will work in older versions of Photoshop as well.

1. Prepare the Image:

Open a new RAW image in Photoshop and edit it as per your preferences. Do note that if you are using a JPEG image straight from the camera, then you might end up over-sharpening it. I have used a close up image of some wildflowers.

Photograph/Sarang Naik

2. Create a Duplicate Layer

If you don’t have the layers panel enabled, then go to the ‘Window’ menu and select ‘Layers’. Now right click on your background layer and select ‘Duplicate Layer’. A pop-up window will appear, where you can change the name of the layer if you wish to. Click on OK after you are done. We now have a duplicate layer. Easy peasy!

Creating a duplicate layer.

3. Apply the Filter:

Now, making sure that the duplicate layer is selected, go to Filter – Other – High Pass.

The path for selecting the filter.

4. Choose the Radius Value

After you select High Pass, the duplicate layer will turn grey. Now as you increase the radius, the layer will get an embossed appearance as the filter selects more and more contrast details. The changes can be previewed in the dialog box.

Adjusting the Radius Value

For high resolution images, a radius value of 2-5 pixels is often quite sufficient. However, since you are working on a separate layer, you can intentionally overdo it and then reduce the opacity of that layer. In this tutorial, I have selected 12 pixels to better demonstrate the effect.

Working on a separate layer allows you to overdo the effect without permanently altering the original image.

5. Change the Blend Mode and Opacity:

Now you have applied the sharpening but the layer is still grey. So time for some magic! In the layers panel, there is a blend mode tab that is on ‘Normal’ mode by default. Open the drop-down menu and select the ‘Overlay’ mode. There! You’ll have your image back, only a lot sharper than before. The effect will probably be overdone, so to reduce it go to the opacity tab and adjust the slider until you are happy with the result.

It is better to overdo the sharpening and then reduce the opacity. This gives you more control over the final result.

That’s it! You now have the final, sharpened image and the effect is quite pleasing and subtle. See the difference in the image before and after sharpening –

For More Selective Control:

Although the high pass filter does a very good job of sharpening the image, it does so at the cost of adding some noise. This noise will be prominent in the plain parts of the image such as a cloudless sky.

You can correct this by adding a layer mask to the sharpened layer and paint away the effect from the parts that don’t need sharpening. This is a bit more advanced technique, but one that gives you great control over the end result.