Sharpening and Blurring

Sharpen and blur at the end of your digital darkroom work flow because they can significantly alter image data. Correct the tone, balance the color, and retouch before sharpening and blurring to minimize banding and data loss due to overmanipulation.

Sharpening and blurring are opposites—one clarifies, and the other obscures. You use both tools to your advantage in Photoshop. You sharpen images to make the edges more visually defined. We prefer images with distinct edges because they resonate with the perception of form in our minds.

Photoshop sharpens images by comparing pixels that differ in value from their neighbors and increases the contrast between them. Within the radius of this comparison, the bright areas get brighter and the darks get darker. Even though no true hard edge is really defined in the matrix of pixels, our visual systems ultimately perceive areas of higher contrast as an edge.

The amount of sharpening required varies in each image and depends on subject matter, resolution, and quality of the digital camera or scanner used to import the image into Photoshop. Every digital photograph benefits from at least a little sharpening.

WARNING You cannot effectively sharpen severely blurred images because there is not enough detail to enhance.

As the contrast between pixels is increased by sharpening, sometimes undesirable color halos appear, especially in images that have extreme levels of sharpening. Halos tend to spread around areas of overly saturated color in sharpened images. To reduce this unwanted effect, you can blur the color halos to remove noise.

TIP When the woven grid of a garment's fibers is close to the scale of the pixel grid, interference patterns, called moires, result. You can remove a moire pattern by blurring the color of the affected regions.

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