Page #184 (148. About Sharpness)

149. Sharpen an Image

Before You Begin

148 About Sharpness

See Also

150 Blur an Image to Remove Noise

151 Blur a Background to Create Depth of Field

152 Create a Spin Effect

153 Soften Selected Details

154 Add Motion to an Image

163 Mask an Image Layer

When you create an image, either by taking a photograph or drawing a picture, you always have a particular point in the image where you want the viewer to focus. This focal point is often referred to as the subject of the image. It is not unusual to take a photo of an object and find that the subject of the photo does not have the desired sharpness necessary to make it stand out from the background.

Improving the sharpness in your images can be a challenge. You often have to increase the contrast between the edges of the subject and the surrounding background. One tool that works well for sharpening an image is the Unsharp Mask filter. When you apply this filter to your image, it locates the pixels in the image that differ from the surrounding pixels and increases the contrast between those pixels. When you use this filter, you control the sharpening effect by specifying the amount of contrast, the number of pixels to sharpen around the edges, and the Threshold, or how different the target pixels need to be from the surrounding pixels.

You can apply the Unsharp Mask to an entire layer or to a selection. Keep in mind that everything within the selection will be affected by the filter. If you don't select a portion of the image, the entire active layer is sharpened. You might want to sharpen only the subject of the image, leaving its surrounding elements as they are so that the subject stands out. To accomplish this, select that subject using one of the selection tools and then apply the Unsharp Mask. See 70 About Making Selections for more information on using selection tools.


Why is the filter called unsharp mask if it sharpens content? As preposterous as it might sound, the way this filter works begins with the act of blurring. In the computer's memory, the filter creates a duplicate of the selected layer or region that you'll never see, and then blurs that duplicate. Mathematically, the product of the data from the duplicate is subtracted from the data from the visible image. The theory is that the remainder of the mostly blurred region combined with a partly blurred version of that same region will yield a cleaner, clearer, and sharper rendering of that region. Don't knock it; it works.

If you want to have more control over how the Unsharp Mask filter affects the final image, you can use an edge mask to apply the filter as explained in this task. In creating an edge mask, you sharpen an image so that the edges of its subject matter are well pronounced. You can then mask the image so that only the edges you select are actually visible to the viewer. For example, in this example of a koala, I want only the koala, and not the tree branches, to be sharp. By masking the koala, you can sharpen only those edges. This way, any background edges that were sharpened by the Unsharp Mask will not display in your final image.

Although Photoshop Elements allows you to create masking effects, you cannot create and save masks as you can with other photo editing software packages such as Adobe Photoshop. Masking works well for hiding portions of an image you don't want to be visible. See 163 Mask an Image Layer for more information on masking portions of an image.


Edge mask A selection that encompasses only the edge pixels in an image, thus preventing unwanted sharpening to everything else.


Create Sharpening Layer

Open the image you want to adjust in the Editor in Standard Edit mode and save it in Photoshop (*.psd) format. If it's not already showing, display the Layers palette by selecting Window, Layers. In the Layers palette, click to select the Background layer and choose Layer, Duplicate Layer from the menu bar to duplicate the background layer. On the Duplicate Layer dialog box, specify a name for the duplicate layer, such as Sharpening. The layer you are creating is where you will apply the Unsharp Mask filter. You want to create a separate sharpening layer so that you can mask out the edges you want visible in the image.


See 92 Create a New Image Layer for more information on adding layers to an image.


Don't worry about oversharpening the background. You are going to use a mask to display only the desired sharpened edges of the subject.

Use the and + buttons to change the size of the image that displays in the preview window.

If you plan to print the image, you'll want the sharpening effects to be more dramatic. Images from printers are not as sharp as they appear on the screen.


Apply Unsharp Mask Filter

With the Sharpening layer chosen in the Layers palette, select Filter, Sharpen, Unsharp Mask. The Unsharp Mask dialog box opens. Enable the Preview check box.


Specify Settings

In the Amount field, specify a value representing the amount you want to increase the contrast between the pixels. For these purposes, you'll want to choose a much higher value than you'd want for a layer you actually intend to keep, such as 200% or higher.

In the Radius field, specify a value that indicates how many pixels around the vicinity of each pixel play a role in adjusting the color to appear sharper. The larger the number, the wider the band of pixels that are evaluated when sharpening each one.

The Unsharp Mask filter adjusts every pixel to some extent based on its evaluation of the color values of its neighboring pixels. The Radius setting determines how many neighboring pixels to evaluate for each pixel being evaluated. Threshold is a relative setting designating how much of a brightness difference between neighboring pixels constitutes a meaningful differencein other words, how much contrast is a contrast that matters. Material contrasts are the ones that are enhanced, so a lower Threshold setting means that more contrasts (by lesser differences) are enhanced.

For the purposes of this task, you want to turn up the contrast along the edges of objects as much as possible. This generally means you should set Radius to a high value (above 50) and Threshold to a low value to compensate. Take a good look at the preview and remember that you're looking for edges to be overemphasized. Click the OK button to finalize your choices.


Create Mask Layer

In the Layers palette, click the Background layer and then choose Layer, New, Layer from the menu bar to create a new blank layer. You can name this layer Mask because it is the layer where you will mask the sharpened edges of the image. You are going to create a mask that includes just the sharper edges of the image.


Group Layers

In the Layers palette, choose the Sharpening layer. Select Layer, Group with Previous from the menu bar to group the Sharpen layer with your new Mask layer.

Notice that the sharpening effects are no longer visiblenow the image looks as it did in step 1. When you group layers, the top layer (in this case, the Sharpening layer) shows through only where there is content in the bottom layer (in this case, the as-yet empty Mask layer). When you paint on the Mask layer in the next step, however, you will allow only selected areas of the Sharpening layer to appear.


If you don't want some of the edges to appear as sharp, you can reduce the Opacity setting for the Brush tool in the Options bar before painting those edges.


Mask Edges

The next thing to do is to add content to the Mask layer where you want the edges of the image to appear sharpened. To accomplish this, you use the Brush tool.

In the Layers palette, choose the Mask layer, and then select the Brush tool from the Toolbox. On the Options bar, select a soft brush style and a brush size that matches the width of the edge you want to sharpen. Make sure that the Opacity setting is 100%, and that Mode is set to Normal. It actually does not matter what you use for your foreground color, although you might want to choose black simply because your marks become more visible in the thumbnail for the Mask layer in the Layers palette.

In the image, paint along the edges of the subject where you want to sharpen. As you paint, the sharpened edges from the Sharpen layer will become visible.

To remove part of a sharpened edge, select the Mask layer and, using an eraser tool, remove the portion you do not want visible. You can also use any of the selection tools to delete part of the mask. For example, you can use the Lasso tool to select part of the mask, and then press the Delete key to remove the selection.


Because this task involves the use of the Unsharp Mask filter as well as masks (a principal feature of Photoshop CS), you might be wondering what the connection is. Despite their labels, they're two different types of masks entirely. It would be less confusing, I admit, if they had different names.


View Results

When you're satisfied with the result, make any other changes you want and save the PSD file. Then resave the result in JPEG or TIFF format, leaving your PSD image with its layers intact so that you can return at a later time to make changes or additions.

The Unsharp Mask filter makes a number of positive corrections to the sharpness of a layer, along with a wide array of really wild and unwanted changes. But with masking, you can paint directly on top of those areas that reflect the Unsharp Mask changes you do want, and leave behind those areas of changes you don't want.

I had a picture of a koala that was taken through a glass window at the zoo. Because the glass made the koala blend into the background, I used the technique described in this task to sharpen the koala without sharpening the background or the tree branches in the foreground.

When I applied the Unsharp Mask, I set the contrast Amount value very high to make sure that the edges got a lot of contrast and so that the sharpness would also be apparent when I printed the image. Sharpening the image this way also made the trees in the foreground stand out, but I choose not to allow the sharp tree branches to carry over when I masked the image. I just wanted the koala to stand out as the main focal point.

When I created the Mask layer, I used a brush wide enough to create the desired edge for my image. Because it was a very high resolution photo, I had to use a fairly large brush size. I outlined the entire koala and also painted over the facial features to sharpen them as well.

Adobe Photoshop Elements 3 in a Snap
Adobe Photoshop Elements 3 in a Snap
ISBN: 067232668X
EAN: 2147483647
Year: 2006
Pages: 263 © 2008-2017.
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