Sharpening the luminance
Using USM can result in colour shifts and artefacts being introduced. Avoid this by only applying the sharpening to the Luminance channel.
Convert the image to Lab Colour mode (Image>Mode>Lab Colour) and then select the Luminance channel in the Channels panel.
Converting to Lab Colour mode results in some loss of image quality, so it isn’t always desirable. It’s better to apply USM to a duplicate layer and blend that layer with the background using the Luminosity Blend Mode.
Sharpening for printing
Apply sharpening at the size the image is to be used at. Different levels are required depending upon how the image is to be viewed.
An image that is to be printed may need a heavier sharpening treatment than one viewed on-screen.
As some printers apply sharpening, it’s important to make a test print or two before making multiple large prints for the first time.
PAGE 1: Why use Photoshop to sharpen photos
PAGE 2: Sharpen photos with Unsharp Mask
PAGE 3: Sharpening the luminance
PAGE 4: Sharpen photos in Adobe Camera Raw
PAGE 5: Sharpen photos with Smart sharpen
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