【牛X的FieldBlur】
Use Field Blur to build a gradient of blurs, by defining multiple blur points with different amounts of blur. Add multiple pins to the image and specify a blur amount for each pin.
The final result is combined effect of all blur pins on the image. You can even add a pin outside the image, to apply the blur at corners.
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Choose Filter > Blur Gallery > Field Blur.
A Field blur pin is placed on the image. Click the image to add additional blur pins.
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Click a pin to select it, and do one of the following:
- Drag the blur handle to increase or decrease the blur. You can also use the Blur Tools panel to specify a blur value.
- Drag the pin to a new location.
- Press Delete to remove it.
Field Blur原理猜测：
1、在1个点的情况下，全屏均为该点的设置。
2、在2个点(A、B)的情况下，2个点将平面分为3部分，1部分显示为A的设置，1部分显示为B的设置，最后一部分为A、B间的羽化。
3、在多个点（大于2个点）的情况下，分为半径内点与半径外点。
1）在半径内的pixel设置为该Pin的设置。
2）在半径外的pixel设置为最近2个Pin的插值。
但是半径如何计算？对于一个pixel，先找到距当前pixel最接近的2个Pin，该2个Pin的间距的15%（也许是其它比例）即为各自的半径。
Photoshop为了傻瓜化操作，并未公布上述原理。