Thursday, February 1, 2007

How to sharpen your image with the Unsharp Mask filter


By Jane Conner-ziser

There is no doubt that photography has gone digital. You may not realize it, but along with the advancements in digitalization also comes loss of sharpness with most images.

"Resolution adds detail and sharpness distinguishes edges."

Fortunately, photographers and photo enthusiasts don't have to settle for dull images. You can sharpen images without getting gritty prints simply by using the Unsharp Mask Filter, a tool found in both Photoshop and Photoshop Elements.

Digital cameras produce images that contain a range of acutance or "softness." Higher acutance equals a sharper image. By using the Unsharp Mask Filter, which exaggerates the light-dark contrast between the edges of an object, you can control the acutance after the shot has been taken.

Why is sharpening so significant? It can reveal fine details that otherwise would never have been seen in the original, making images appear more crisp and clear. Examples of this include architectural details of a building, subtle facial features and more. As a rule of thumb, remember that every digital picture needs to be sharpened.

It is important to note that resolution and contrast, while both valuable, are very different. A high-resolution image cannot add sharpness. Resolution adds detail and sharpness distinguishes edges.

You use unsharp to make sharper? Huh?

Many users are often confused why something called an "unsharp mask" is used to sharpen images. Wikipedia has a good explanation:

The "unsharp" of the name derives from the fact that the technique uses a blurred, or "unsharp", positive to create a "mask" of the original image. The unsharped mask is then combined with the negative, creating the illusion that the resulting image is sharper than the original.

Let's see it in action

Let's start with the sample image, shown in Figure A.


This is a nice image, but it could be sharper. (click for larger image)

To begin, you will want to sharpen each image to the size you would like it to print. For best printing, use 200 to 300 ppi resolution. In this example, we are using 240 ppi and are viewing the image at 100% in Photoshop.

In Photoshop or Photoshop Elements, go to Filter > Sharpen > Unsharp Mask.

In the magnifier preview window, move your curser over a part of the photo that has good contrast between dark and light areas of the image.

To ensure that you do not over contrast your image, use the Unsharp Mask moderately, as you can see in Figure B.