Getting the High Pass Filter Effect in Pixelmator

EDIT: Before this tutorial even got cold, the Pixelmator Tutorial Podcast picked up the technique and improved on it! Be sure to check out their slightly different method which allows for greater control by allowing you to visualize the sharpening effect.

I recently canned Adobe Photoshop and switched to Pixelmator. No, Pixelmator is not yet everything that Photoshop is. It is missing key items like vector tools (one could argue that Photoshop should not have had them anyway), but Pixelmator is catching up really fast. Pixelmator might even have a leg up on Adobe in a number of areas — like that fact that is looks, smells and feels like a Mac app from this decade.

One thing I found missing that I use quite regularly in photo enhancement work is the high pass filter. A high pass filter is a great way to add some sharpness to your images if you find the edges a little fuzzy. You may not be aware, but the high pass filter in Photoshop is little more then an inverted, blurred copy of the original. It’s easy enough to create manually, but having the feature built into Photoshop made it quick and easy.

So my plan is to write some AppleScript to make happen in Pixelmator. Unfortunately Pixelmator doesn’t yet have an AppleScript Dictionary, so such a script is going to have to be done with what we call menu scripting. Until I have time to sort that out though, here is how you manually emulate the high pass filter found in Photoshop.

1. Duplicate your original layer (⌘J)

image showing layer duplication

2. Name the duplicate “high pass”

image showing the renaming process

3. Remove the color

You want to remove the color but preserve the luminescence of the image, so the easiest way to do this is with Edit > Fill (⌥⌘F), then choose black, and the blending option color. Keep the opacity at 100% and click ok.

image showing color removal

4. Duplicate “high pass” (⌘J) and Invert (⌘I)

image showing inversion

5. Add Gaussian blur (Filter > Blur > Gaussian)

Add as much or as little Gaussian blur to the duplicate as you need. The radius will directly correlate to the number you would have used in your Photoshop high pass filter setting. I typically used between 4 and 20, depending on the amount of sharpening I was after, but you are welcome to go to any extreme you like.

image showing gaussian blur being added

6. Set Blending to Linear Light and Opacity to 50%

image showing blending

7. Merge “high pass” layers

image showing the merging process

8. Set the Blending of “high pass merged” to overlay and enjoy!

image showing new high pass filter