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Undoubtedly, there are times that you may want to increase the perceived clarity or sharpness of an image that you are processing.

Many photo editing software titles allow for sharpening, but there are often several options, only one of which you want to use.

The most common mistake that I see when people are post processing their images is that they oversharpen their work. The amount of sharpening needed for an image is very subjective, but professionals agree that there is a limit to which you should sharpen your images. Stock photo agencies will not take oversharpened photos, nor will most publications. Art is a different story, and indeed, this is what many people classify their photography as. After a while, it becomes a sticky area of discussion.

In this tutorial, we'll do the following:

1) Learn about which images need sharpening, and which are likely not to.
2) Learn about which method of sharpening to use, and how to use it.
3) Learn how to tell if you are oversharpening your images.
4) Learn how to selectively reduce sharpness in certain areas of your image using the history brush.

1) Suggestions for what and what not to sharpen

First, I'd like to suggest the types of images that are not often sharpened, or those that I would recommended not be sharpened.

Portraits, par exemple, are images that should be sharpened with great caution. Human skin, by nature, is something that is not necessarily flattering to see in extreme detail. The camera and lens can bring out much more detail than we're used to seeing, and this can only be exacerbated by sharpening the image. The face and eyes are usually the main point of focus in a portrait, so take care to focus your camera in on them. They may need to be slightly sharpened later (along with the hair). The other details may need to be softened, not sharpened, so don't touch your remote, as I'll explain how to do this soon.

Click for full size

Do not attempt to sharpen yet!

Sunset and sunrise pictures - anything with strong directional lighting needs only minimal sharpening. During the early morning or evening, we see silhouettes or outlines of objects, nothing with hugely defined lines. If it's a landscape with well-lit detail, then you may want to re-think this.

Click for full size

This image doesn't necessarily need

sharpening, but the birds and the buildings in

the background could be slightly sharpened to bring out detail.

Otherwise, almost any image could benefit from a little bit to moderate amounts of sharpening. Landscapes with a lot of grass or trees are great so sharpen up. At long distances from the camera, trees and grass are not resolved very well by the camera's lens and imager. These need to be sharpened more than other things we typically sharpen. (However, be careful sharpening landscape shots - you don't want to oversharpen clouds and/or sky as it makes them look unnatural.) Sports and action images can benefit fron modest amounts of sharpening as well.

Click for full size

Brush and water benefits from rather aggressive sharpening.

2) Which method of sharpening do I use? How do I use it?

One common mistake is when people use the photoshop (or other program) filter that says "sharpen" or "sharpen more." There is an option near those that is called "Unsharp Mask." We like to call it USM for short, but don't get it confused with Canon's lens focusing mechanism, the UltraSonic Motor (USM). The term Unsharp Mask originates from film darkroom use when physical tools would be used to bring out local contrast in areas of an image. Unsharp Mask is, by far, the most commonly used and control-able filter to sharpen digital images.

The one absolutely essential thing to learn about sharpening is that you cannot make an image sharp if it was originally soft when you took it. Unsharp Mask is not magic. It utilizes the detail already in the image to bring out (what I earlier referred to as) perceived sharpness. I (not to mention, others) can tell if you overuse this tool to try to fix a poorly focused image! Soon we'll learn how, but first we've got to learn how to use this mysterious tool/filter.

In photoshop, the Unsharp Mask filter is found in the "Filter" menu under "Sharpness."

The dialogue box looks like this:

Click for full size

"Amount" is how much sharpening you want to apply. "Radius" is the most important box to look at, as it denotes the type of sharpening you will be applying to the image. "Threshold" is, in short, the sensitivity of the image to the tool.

Let's start with "Radius." If you have an image with very small details you want to bring out, you should set the radius low. For very small details, I use a 0.2 pixel radius. For larger (but still small) details, or images that are slightly soft, I use a larger radius, between 0.3 and 0.9 (or 1). This will enhance the small details in an image. If you use a larger radius, you can enhance the contrast of the entire image, with emphasis to detail areas. For doing so, I would use something between 5 and 50 pixels.

Now, with "Radius," the "Amount" is what you use to control how much of your sharpening is applied to the image. This is probably the easiest part to remember, and is very obvious if you get it backwards: The larger the Radius, the smaller the Amount is needed. The smaller the Radius, the larger the Amount is needed. For anything under a 1 pixel radius, you'll need to use a pretty large amount (percentage) to notice any difference in your image, something between 100% and 500%. For a large-pixel radius, you can use a smaller Amount, e.g., something between 1% and 40%.

The "Threshold" is easy. If it is set low, the image will be affected more easily by the sharpening. I usually keep the threshold set between 0 and 5. I almost never touch it.

Now, all of this information is useless without an example of how to use it in a workflow. I am a fan of often using a 2 step USM application - one step with a high pixel radius sharpening to bump local contrast, and another with a lower-pixel radius to bring out the little details in the image.

Note that sharpening should always be the last step in your workflow. I do not recommend sharpening full-sized images if you intend on resizing them and posting them online. All of the specs I have given for sharpening are for images between 600x400 and 1500x1000 resolution. Always save a copy of your work, never overwriting the original copy. If you are going to be sending a file off for print, you'll need much larger pixel radii, even for small details.

Let's try one out!

Here's an image that has gone through a full workflow but has not been sharpened yet. It has been resized to 900x600 pixels:

Click for full size

Step 1: A first-step, high-pixel sharpening. This boosts the dramatic contrast in the picture, but not enough to kill all of the blacks or blow the highlights like using another method might.

Click for full size

Amount: 20%, Radius: 5px, Threshold: 0

Step 2: A second-pass, smaller-pixel sharpening. This will bring out some detail in the leaf and the spider webs.

Click for full size

Amount: 270%, Radius: 0.2px, Threshold: 0

Voila! We've made it - a final image, ready for posting on your online gallery or friendly DSLR DI board!

Stick with us though; this is a modestly-sharpened image. Let me show you what happens when disaster strikes (and it strikes more often than you may think!) Read on....

3) Oversharpening

Oversharpening usually originates from doing one of two things:
•Using the "sharpen" or "sharpen more" options in your editing software.
•Using too high of a USM pixel radius with too much power (amount/percentage)

Here is the above image sharpened excessively (for small details) with too high of a pixel radius:

Click for full size

Here's that same image that was sharpened too many times with a low pixel radius:

Click for full size

How do I tell if I've oversharpened my image?

Color noise and tiny artifacts (that normally wouldn't be seen if left alone) are brought out in oversharpening. While multiple low-pixel sharpening passes can be done, the above was an example of how far not to take it. The excessive high-pixel sharpening will cause halos around objects. I would say that this is the most common error. It happens a lot with portraits against solid-colored backgrounds, and you end up seeing halos around the person's head, hand, etc.... If in doubt, back it off a little bit and look at it in comparison to your original image.

4) Selectively reducing sharpness with the history brush

While the history brush could have an entire tutorial of its own, the history brush has a great purpose for touching up the sharpness in portraiture or other photos that have different sharpness requirements for every section of the image.

Let's take a look back at the types of images that might need this special treatment:

•Landscapes that have trees and sky in the same image
•Images that need low-pixel sharpening, but have places where artifacts might be brought out in empty space or in undesirable areas

Here's our original portrait:

We want to do some low-pixel sharpening to the entire image to begin with. Look only at the face/eyes/hair when doing this part.

Click for full size

Two passes, one at .3px and one at .2px. Her face/hair look sharp

Now, open up the history pane, it looks like this:
Click for full size

See that little brush and the arrow at the first step for this image? That's the anchor for the history brush. It allows you to paint over any area of the image, and the image will be restored to that history state. Click the history brush box for the state right before the sharpening began, and it will look like this:

Click for full size

Now, locate the history brush on your tools panel:

Use this brush to brush away the sections of the image you didn't want sharpened. In this photograph, I want sharpness only in the face/hair. All other skin and clothing (and the tree that the camera back-focused on) should be brushed back to it's pre-sharpened state. With that, the final image looks like this:

Click for full size

The subject is properly sharpened in the right places, and unnecessary sharpness in distracting locations has been taken away!

Take a look at the tutorial for the history brush if you have any more questions.You can acheive a same effect with a greater degree of control (with added difficulty/complexity as well) with a layer mask. Read about layer masks here.

Proper sharpening should leave little or no trace of its presence in your final image. I like to say this as a loose rule of thumb: If anybody else can tell that it's been sharpened, you've done too much of it.

Thanks for reading!

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by DavisPhotog See Profile edited by climbers See Profile
last modified: 2005-12-31 01:54:23