我在http://developer.apple.com/library/mac/#documentation/graphicsimaging/reference/CoreImageFilterReference/Reference/reference.html#//apple_ref/doc/filter/ci/CIColorControls查看 Core Image Filter Reference 的 CIVignette
并玩弄参数： inputRadius inputIntensity ，但仍然没有完全理解每个参数的影响。可以请人解释一下吗？
Take a look at wiki understand what vignetting in photography means.
It is the fall of of light starting from the center of an image towards the corner.
Apple does not explain much about the the params.
obviously the radius specifies somehow where the vignetitting starts
the param intensity i expect to be how fast the light goes down after vignetting starts.
The radius may not be given in points, a value of 1.0 relates to your picture size.
强度绝对是 1 到 10 或更大的数字。1有一些效果，10已经相当暗了。
半径似乎以像素（或点）为单位。我使用了一部分图像尺寸（比如宽度的 1/10），效果还不错！但是，如果强度很大（例如 10），则半径可以很小（例如 1），您仍然可以看到不同之处。