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USM sharpening is a function often used in the image revision process to enhance the details of the edges of objects, but it will also affect the image quality in the process of sharpening. This tutorial will explain the parameter effects and sharpening methods of sharpening.

This is the USM sharpening in Photoshop. In the sharpening of the filter, it is often used to enhance the edges of objects in various parts of the picture, such as the texture details of human eyes, hair, animal feathers, and scenery.

In the interface, there are three adjustment parameters "quantity, radius and threshold". What kind of effect are these three parameters responsible for? let's take a look at them:

1. Quantity

This is what it looked like before sharpening.

This is the effect of a quantity of 300

This is the effect of a quantity of 500

It can be seen from the effect that sharpening is actually increasing the contrast of the edge, and the parameter "quantity" is responsible for the strength of the contrast. the larger the number, the stronger the contrast, the more obvious the sharpening.

2. Radius

Quantity and threshold remain the same, radius 10

The quantity and threshold remain the same, with a radius of 50

It can be seen from the effect that the parameter "radius" is responsible for the range of contrast. The larger the radius is, the larger the sharpening range is, and the influence on the surface of the object will increase, spreading from the edge to the surface. If we only want to sharpen the edge texture and do not want to affect the surface, the radius should not be too large.

3. Threshold

The quantity and radius remain the same, the threshold is 10

The quantity and radius remain the same, the threshold is 50

The threshold is an index for judging the edge pixels of each part, using the threshold to delimit the range of pixels that will be sharpened, and using the brightness of the color as an index, such as a threshold of 10, if the brightness difference between the edge pixels is less than 10, the effect will not be applied, and only the part where the brightness difference between pixels is greater than 10 will be sharpened. So the larger the threshold, the smaller the scope of sharpening is applied.

The difference between the threshold and the radius is that the radius is the range only in the distance, the threshold is based on the color lightness, and the influence on the range is not the same as the radius. Usually when revising the picture, the threshold is between 2 and 10.

Sharpening above we take the black-and-white edge as an example to demonstrate the sharpening effect. In the black-and-white effect, sharpening only increases the edge contrast and does not affect the color.

But what if you change it to a color picture?

This is unsharpened.

This is after USM sharpens.

After sharpening, other colors will overflow on the edge of the color picture, such as cyan here, which will greatly affect the color purity of the picture.

Therefore, in order to solve the problem of color overflow, we need to sharpen the brightness.

First stamp a viewing layer, and then select "Lab Color" in the mode in the upper menu bar.

There will be a hint that we choose "not to put it together."

In the channels panel, check the lightness and close the small eyes in front of the other channels.

Then select USM sharpening to adjust the sharpening parameters appropriately. After the adjustment is completed, change the mode from Lab to RGB, and the color will be restored, but there is no color overflow problem at this time.

After sharpening, the edge is only a change in contrast, and there is no other noise overflow.

Most of our pictures are in color, so in USM sharpening, we first do brightness processing to get the best picture quality. And be sure to remember that sharpening is mainly to strengthen the edges of the objects in the picture, which has little impact on the surface. If you want to strengthen the surface, you can use high contrast retention or nik plug-ins.

This article is from the official account of Wechat: light and Color World of Shadow Leaf (ID:wangyikai-2016). Author: shadow Leaf.

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