When you resample an image in Photoshop Creative Suite 5, it can become blurry. A good practice is to apply the Unsharp Mask filter. You can see the difference in detail in the images. This feature sharpens the image based on levels of contrast while keeping smooth the areas that have no contrasting pixels. You have to set up this feature correctly to get good results.

Here’s the down-and-dirty method of using the Unsharp Mask filter:

  1. Choose View→Actual Pixels or double-click the Zoom tool.

    When you’re using a filter, view your image at its actual size to best see the effect.

    The image without (left) and with (right) unsharp masking applied.
    The image without (left) and with (right) unsharp masking applied.
  2. Choose Filter→Sharpen→Unsharp Mask.

    In the Unsharp Mask dialog box that appears, set these three options:

    • Amount: The Amount value ranges from 0 to 500. Your choice depends on the subject matter. Sharpening a car at 300 to 400 is fine, but do this to the CEO’s 75-year-old wife and you may commit career suicide because every wrinkle will magically become more defined. If you’re not sure which amount to use, start with 150 and play around until you find the right Amount value.

    • Radius: The Unsharp Mask filter creates a halo around the areas that have enough contrast to be considered an edge. Typically, leaving the amount between 1 and 2 is fine for print, but if you’re creating a billboard or poster, increase the size.

    • Threshold: This option is the most important one in the Unsharp Mask dialog box. The Threshold setting determines what should be sharpened.

      If you leave it at zero, you see noise throughout the image, much like the grain you see in high-speed film. Increase the setting to 10 and it triggers the Unsharp Mask filter to apply only the sharpening when the pixels are ten shades or more away from each other.

      The amount of tolerance ranges from 1 to 255. Apply too much and no sharpening appears; apply too little and the image becomes grainy. A good number to start with is 10.

    To compare the original state of the image with the preview of the Unsharp Mask filter’s effect in the Preview pane of the Unsharp Mask dialog box, click and hold the image in the Preview pane; this shows the original state of the image. When you release the mouse button, the Unsharp Mask filter is previewed again.

  3. When you’ve made your choice, click OK.

    The image appears to have more detail.

Once in a while, stray colored pixels may appear after you apply the Unsharp Mask filter. To fix this, choose Edit→Fade Unsharp Mask immediately after applying the Unsharp Mask filter. In the Fade dialog box, select the Luminosity blend mode from the Mode drop-down list and click OK. This step applies the Unsharp Mask filter to the grays in the image only, thereby eliminating the sharpening of colored pixels.

You can also choose Filter→Convert for Smart Filters before you apply the Unsharp Mask filter. Smart filters let you undo all or some of any filter, including sharpening filters you apply to a layer.