(PECL imagick 2.0.0)
Sharpens an image
bool Imagick::unsharpMaskImage ( float $radius, float $sigma, float $amount, float $threshold [, int $channel = Imagick::CHANNEL_ALL ] )
Sharpens an image. We convolve the image with a Gaussian operator of the given radius and standard deviation (sigma). For reasonable results, radius should be larger than sigma. Use a radius of 0 and Imagick::UnsharpMaskImage() selects a suitable radi