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You can sharpen images to increase contrast, enhance image edges, or reduce shading. Sharpening is usually done after adjusting the color and tone of an image and after resampling or resizing. For information about the Sharpen special effects, see Sharpening images.
The Adaptive unsharp effect (Effects 
Sharpen Adaptive unsharp) lets you accentuate edge detail by analyzing the values of neighboring pixels. This filter preserves most image detail, but its effect is most apparent in high-resolution images.
The Directional sharpen effect (Effects Sharpen Directional sharpen) lets you enhance the edges of an image without creating a grainy effect.
The High pass effect (Effects Sharpen High pass) lets you remove image detail and shading to give an image a glowing quality by emphasizing its highlights and luminous areas. However, it can also affect the color and tone of the image.
The Sharpen effect (Effects Sharpen Sharpen) lets you accentuate the edges of the image by focusing blurred areas and increasing the contrast between neighboring pixels. Move the Edge level(%) slider to set the degree to which edge detail is accentuated. Threshold specifies how far apart adjacent tonal values have to be before the effect is applied. This is important to prevent smooth areas from becoming speckled. Low values produce a more exaggerated sharpening effect because fewer areas are excluded. Higher threshold values exclude areas of lower contrast. To prevent dramatic shifts in hue, enable Preserve colors.
The Unsharp mask effect (Effects Sharpen Unsharp mask) lets you accentuate edge detail and focus blurred areas in the image without removing low-frequency areas. Percentage sets the intensity of the sharpening effect. Radius sets the amount of pixels that are evaluated at once. Threshold sets how many pixels are affected.
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