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Photoshop provides four sharpening options in its Filter Menu but the only sharpening filter you will really need is UNSHARP MASK. This sounds like a contradiction, but in fact it arises from a process where a soft unsharp negative was sandwiched next to the original positive image during exposure. This resulted in an increase in edge sharpness. Thankfully Photoshop does all of this work for us digitally.
Not all images need to be sharpened, but if they do, it is preferable to do this as the last process in the image manipulation. Many scanners have a sharpening feature built into their software and it is better to switch this off and do your sharpening as the last act of manipulation in Photoshop before going to save and print. To find the Unsharp Mask Filter go to the top menu bar and FILTER as shown here - 
There are three aspects to the Unsharp Mask Filter The AMOUNT setting controls the intensity of the sharpening to be applied. The higher the percentage the greater the sharpening effect. Typically. I apply an amount of 150 to 200%. The RADIUS setting controls the width of the sharpening effect. The recommended setting is between 1 and 2. As higher settings are chosen the the edges are emphasised more. The THRESHOLD setting controls which pixels will be sharpened. - this is based on the deviation of brightness from one pixel to its neighbouring pixel. At lower settings more or all of the pixels are sharpened including areas of continuous tone. Higher Threshold settings apply the filter only to neighbouring pixels which are markedly different in tonal brightness, e.g. edge outlines. Raising the Threshold setting will enable you to sharpen edge contrast, but without sharpening any scanner noise or film grain which may be already evident. This screenshot shows the typical settings I would use to tweak the sharpness in an image. Note that by ticking the "Preview" box I see the sharpening effect before I press OK to select the setting. 
Now, go experiment!! Author: Harry Reynolds Discuss this article on the forums. (0 posts) Very good article.
I usually find the following works for me,
Amount: 120%
Radius: 1
Threshold: 0 |
