Sometimes an image may not be as clear as you'd like it to be. Sharpening can help to make your images look crisp and clear by enhancing the edges of objects in the image. However, adding too much sharpness can actually make an image look worse, or it can lead to a loss in image detail. Take a look at the example below:
As you can see, the right amount of sharpness makes the photo look crisp—for example, in the center image, it's easy to see the edges of the bird's feathers. But adding too much sharpness can cause the edges to look exaggerated and unnatural (these are known as halos), as in the image on the right. You may have also noticed that the background in the oversharpened image has a lot of added image noise, or graininess. We'll talk more about reducing image noise on the next page.
Whenever you apply sharpening, you'll need to look critically at the image to see if you're getting the results you want. You'll often need to make careful adjustments to get the right amount of sharpening without introducing other problems like halos or noise.
The unsharp mask filter is a common way to sharpen images in Photoshop. When you use this tool, you'll be able to control a few different settings, including:
- Amount: The amount determines how much sharpness will be applied. The amount you'll need depends on several factors, including the overall image size, so it's good to experiment with this setting.
- Radius: The radius controls the size of the details that will be sharpened, so it's generally best to use a very low value for this setting. We recommend a radius between 0.3 and 0.5 for most images, although you may find it useful to use a slightly larger radius (between 1 and 1.5) for higher-resolution images.
- Threshold: Sharpening tends to make image noise more visible. Increasing the threshold can help to reduce this by telling unsharp mask to ignore certain parts of the image. However, this can also mean that different parts of the image are not sharpened consistently. This is why we recommend keeping this setting at 0 most of the time, unless the sharpening is creating a lot extra noise.
To apply an unsharp mask:
- Right-click the layer you wish to sharpen, then select Duplicate Layer. You'll apply the sharpening to this duplicate layer, which will prevent you from accidentally altering the original.
- A dialog box will appear. Type a name for the new layer, then click OK. In this example, we'll call it Sharpened.
- With the new duplicate layer selected, go to FilterSharpenUnsharp Mask. If you're using Photoshop Elements, you'll need to go to EnhanceUnsharp Mask.
- A dialog box will appear. Set the desired radius size, then choose the amount of sharpness to add. We recommend experimenting with different amounts of sharpening to see what looks best. You can look at the preview window above the sliders to see how sharpening is affecting the image.
- Click the preview window to toggle the preview off and on. This is an easy way to compare the sharpened version with the original. To view a different part of the image, you can click and drag within the preview window. Note that you'll also see the preview in the main document window.
- Continue to adjust the settings until you're satisfied with result, then click OK. The unsharp mask will be applied.
Open the hawk_fullsize.jpg example file, duplicate the background layer, and apply an unsharp mask. Adjust the settings to find a balance between sharpness and a loss of detail.
If you want to learn even more about sharpening, check out this tutorial from Cambridge in Colour.