How to Use Unsharp Mask – The World’s Simplest Definition
All (and we do mean all) of your photos are blurry and out of focus.
You may think they look okay, but they all could look a lot better. This article will tell you how to sharpen and enhance any photo to make them look clearer and more in focus.
We as humans have a tendency to tolerate soft or out-of-focus photos unaware they can be dramatically improved. You would think high quality cameras and scanners would produce sharp images but that’s not the case. The process of transferring a three dimensional view into two dimensions mashes and destroys edges of items in photos.
This is the world’s simplest definition of an oddly named function that will brilliantly sharpen any photo and may already be in a program you own. The term is called Unsharp Mask. If you don’t know what that is, you should. Lots of photo software programs have the Unsharp Mask function. Using photo editing software you can apply this procedure to make any photo sharper with more visual appeal.
The benefits of this Unsharp Mask procedure are well known in the printing and graphics arts industries and have been for decades. Think about it for a moment; the older the photo or movie, the blurrier or more out of focus it is. Photos and movies became sharper through the years as these industries used a hardware version of the Unsharp Mask technique well before digital camera days.
Unsharp Mask is an overlooked way to improve photos that would make many of them pop off the screen or page. This is likely because few people understand it. All definitions of the term Unsharp Mask seem to be impossibly technical and difficult to grasp.
Greatly simplifying the actual process, if you took a picture, copied it, made the copy slightly more blurry than the original then blended the two back together, you would end up with what looks like the faint ghost of the original image. This is the filter or “mask” that Unsharp Mask uses.
Unsharp Mask recreates an image using the original, filtered through this mask like water through a water filter – the ghost or filter image defines edges more sharply than the original when mixed again. This resharpening or Unsharp Mask procedure always improves images to some degree and often results in an amazing, three dimensional look that visually grabs and absorbs you much more than the original.
There are five terms needed to understand Unsharp Mask. Most explanations have three: Amount, Radius and Threshold but understanding two more terms may help to understand it better:
Areas where items in an image begin and end. All objects have edges that are more or less clear or defined. Some objects will have gradual changes from one edge to the next, and others will have sudden changes. A waterfall will have many gradual edges. Buildings tend to have sharply defined or sudden edges.
Technically this is defined as adjoining areas having significantly different hue or tone. More simply a tone shift is the boundaries of places in the image where significant content changes. Think of a tone shift as the edge of one object and its opposite edge flipped over of the area that the edge is touching. Very simply, a tone shift is a double-edge.
Tone shifts have varying degrees of strength themselves depending on whether the content is gradually changing from one result to another, or whether the content change is abrupt or sudden as you look across the image. If you can grasp the concept of a tone shift, then the three values of the Unsharp Mask function become much more understandable:
Amount. Tone shift contrast.
Radius. Tone shift size.
Threshold. Tone shift definition.
That’s the shortest, simplest explanation you’ll find for these concepts, and while this greatly oversimplifies their meaning thinking of the three Unsharp Mask settings in this way can allow you to actually use it in photo editing software with more success. These three concepts more fully explained:
Tone shift contrast amount. The amount is a percent number used to tell Unsharp Mask how much contrast that will be added to tone shifts.
Tone shift size amount. Tells Unsharp Mask how big or wide the tone shifts are. Radius has been referred to as giving tone shifts a glow or halo effect, especially if overused.
Tone shift detail definition. Tells Unsharp Mask how wide a tone shift must be for it to be considered a tone shift. This allows Unsharp Mask to be applied without amplifying image noise or fine detail that doesn’t need sharpening.
Unsharp Mask Settings.
The numbers that actually go into the three values of Amount, Radius and Threshold can also be confusing. This is because the numbers are not of the same type and photo software can have their own definitions (and even names) for these settings. Amount is a percent, Radius is a number that can represent pixels or sometimes down to one-fourth of a pixel depending on the photo software, and Threshold is most commonly a value from 0 to 5: 0 will define everything as tone shifts to be sharpened, 5 will define only the largest tone shifts to be sharpened and beyond 5 usually has little effect because hardly any edge will be defined as a tone shift. However photo editing software can define the Threshold number setting much differently.
Because Unsharp Mask settings can be difficult to understand by reading the definitions, use photo editing software that has slider bars to get a feel for how Unsharp Mask behaves. The photo software should also show an automatic preview of the result as slider positions change. Photoshop®, Paint Shop Pro® and a photo enlargement software product called Imagener – www.imagener.com – have the Unsharp Mask with auto-preview function built into them. Imagener shows automatic previews of the full size image. Most photo software programs show just a piece of the image in a small window.
It takes practice to come up with the right combination of Unsharp Mask settings for an image, but use it if you have photo software that has Unsharp Mask keeping at least the simple definitions above in mind. All images will look better with Unsharp Mask applied – many times images are improved so much you will be amazed with the results.
General Guidelines Setting Unsharp Mask Values
Again, Amount refers to the intensity of the Unsharp Mask effect. A setting between 100% and 200% will do, depending on the next setting – the Radius. The bigger the Radius, the less Amount needed. One “standard” Amount setting to start with is 120% however, some images need more than this, others less of course.
Radius refers to the dimension, in width, of every sample that will be affected. Choose a setting between 1 and 1.5, depending on the resolution of the image. The higher the resolution of the image, the greater the setting should be for Radius. Complex images will look better with different settings than images with simpler content. For example, try a Radius setting of 1 for a 200 dpi (dots per inch) image and a Radius settign of 1.5 for a 300 dpi image. Again the more Amount you use, the less Radius is necessary.
The Threshold setting tells the software how many numbers of samples in an image will be sharpened. A setting of zero will affect every sample, whereas a setting of 50 will affect almost none of the samples. Highly detailed images such as line art require a setting of 3; whereas portraits look best with a setting of 5 to 9 (trying to keep minor wrinkles down to a minimum). It takes practice to come up with the right combination of settings for an image, but all images will look better with Unsharp Mask applied.
Every image is unique. For purposes of Unsharp Mask this means that there are no “common” or “default” values for Amount, Radius and Threshold. But there are some beginning guidelines that you can use to begin your testing. Keep in mind the following guidelines regarding the three values of Unsharp Mask:
Unsharp Mask General Guideline One: Image Consists Mostly of Fine Details
Set a strong amount of sharpening, with very small radius and a low threshold, such as Amount: 200, Radius: 1-2, Threshold 1-2. This improves all boundaries in the image over a small distance. While these settings will also increase grain or noise, they will be hidden by the detail.
Unsharp Mask General Guideline Two: Image has large areas of even tone
Set a modest amount of sharpening, and a large radius with a relatively high threshold, such as Amount: 50, Radius: 20, Threshold: 10. The high threshold ignores noise while the high radius compensates for the moderate amount.
Set Unsharp Mask Settings Visually with Imagener
As briefly mentioned above, a stand-alone photo enlargement program called Imagener by Kneson Software can be used without the enlargement function to visually and automatically apply Unsharp Mask resharpening to images. The full size of the image is displayed in Imagener’s Result window, and if the “Auto” checkbox is checked (see image to the right) just moving the sliders back and forth shows the effect of changing the three Unsharp Mask values. Order Imagener today.