Gradually shades the edges of the image by transforming the pixels
into the background color.
Larger values of sigma increase the blurring at the expense of
increased execution time. In general, radius should be larger than
sigma, although if radius is 0 then ImageMagick will choose a suitable
value. Sigma must be non-zero. Choose a very small value for sigma to
produce a "hard" edge.
Gradually shades the edges of the image by transforming the pixels into the background color.
Larger values of sigma increase the blurring at the expense of increased execution time. In general, radius should be larger than sigma, although if radius is 0 then ImageMagick will choose a suitable value. Sigma must be non-zero. Choose a very small value for sigma to produce a "hard" edge.