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Up-to-date documentation:

Blur(clip clip, float amount, bool MMX)
Blur(clip, float amountH, float amountV, bool MMX)

A 3×3 kernel blurring filter.

Sharpen(clip clip, float amount, bool MMX)
Sharpen(clip, float amountH, float amountV, bool MMX)

A 3×3 kernel sharpening filter; the inverse of Blur.

float  amount = (required)

The allowable range for Blur is from -1.0 to +1.58
The allowable range for Sharpen is from -1.58 to +1.0
Negative Blur actually sharpens the image; in fact Sharpen(n) is just an alias for Blur(-n).

float  amountH = (required)
float  amountV = (amountH)

You can use 2 arguments to set independent vertical and horizontal blurring or sharpening: for example,
will blur vertical only, perhaps to blend interlaced lines together.

bool  MMX = true

This option should always be true.

[edit] Notes

If you need a larger radius Gaussian blur, try chaining several Blurs together:


Chaining calls to Sharpen is not a good idea, as the image quickly deteriorates.

[edit] Developer notes

Blur uses the kernel [(1−1/2^amount)/2, 1/2^amount, (1−1/2^amount)/2]. The largest allowable argument for Blur is log2(3) (which is about 1.58), which corresponds to a (1/3,1/3,1/3) kernel. A value of 1.0 gets you a (1/4,1/2,1/4) kernel for example. Likewise Blur(1.0).Blur(1.0) is a convolution of the kernel (1/4,1/2,1/4) with itself, being a (1/4,1/2,1/4)*(1/4,1/2,1/4) = (1/16,4/16,6/16,4/16,1/16) kernel. It can be read of Pascal's triangle.

[edit] Changes

v2.58 MMX routines fixed (have full 8 bit precision now); mmx=true by default
v2.57 added MMX option
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