About The Unsharp Mask Filter…
Photoshop’s Unsharp Mask Filter is the most common sharpening tool used by photographers during post production. Although its name sounds like an oxymoron when the goal is to actually sharpen an image, it definitely does exactly that — sharpen. Well, sort of. Applying the Unsharp Mask Filter actually results in the illusion of sharpening, where the human eye is tricked.
Too Much Of A Good Thing
Most photographers new to Photoshop have a tendency to do a bit of overkill when first learning the program and experimenting with its filters. I know I was certainly guilty of that in my early days with the program and my entry into the world of digital post production.
Use of the Unsharp Mask Filter is certainly one area where lack of experience — or limited understanding of the filter’s slider controls (Amount, Radius, and Threshold) — visibly shows its hand.
The sharpening error that most often appears in the details of certain images is called “halos.” However, halos are not always due to inexperience and overkill. There are times when halos are just a byproduct of a perfectly legitimate use of the Unsharp Mask Filter.
Regardless of whether due to inexperience or a legitimate byproduct, halos are ugly and distracting.
What Exactly Are Halos?
Halos are those white (sometimes dark) lines that appear between highly contrasted areas. View your images on-screen at 100% and really check the edges of your subject matter. While halos might not be that visible in a small size print, they will be exponentially more visible in larger print sizes. Definitely not a good thing!
Let’s Take A Look
Here’s an example where I deliberately oversharpened my image. At first glance the overkill might not look too obvious. Don’t be fooled. Halos are indeed there.
Now Let’s Take A CLOSER Look
When we zoom in to take a closer look, you can clearly see that oversharpening produced very noticeable halos along the edges of the lighthouse (as well as along the railing, rocks, and horizon in the full image above). Can you imagine just how obvious and distracting that would be in a nicely framed large size print? Ugh! That’s why it’s important to always check the details in your images on-screen at 100%.
Now if I noticed the halos during my initial post production of this image, I could immediately correct the flaw by making some adjustments to the Unsharp Mask Filter control sliders. But what if I only discovered the halos after the fact?
Don’t panic. It’s never too late to correct the problem.
To start, find your current “final” image file and open it in Photoshop.
How to Fix Halos In Your Images
As with most things in Photoshop, there are several different methods on how to do something. This includes fixing halos. Most techniques for fixing halos have one thing in common — selecting the Darken (or sometimes Lighten) layer blend mode.
Here are a few different video tutorials to show you how to remove halos in greater detail. Try the different techniques and decide which method works best for you and your image.
Unsharp Mask Tutorial
Let’s go back to basics for a moment. For those of you new to Photoshop or those of you simply in need of a quick refresher on the Unsharp Mask control sliders, Adobe’s Principal Digital Imaging Evangelist, Julieanne Kost, has a great video tutorial on the very subject.
In A Nutshell
Before you have prints made from your files, do yourself a favor — check for halos first. You’ll be glad you did.
~ Liz Mackney