(PECL imagick 2.0.0)
Adjusts the contrast of an image
bool Imagick::sigmoidalContrastImage ( bool $sharpen, float $alpha, float $beta [, int $channel = Imagick::CHANNEL_ALL ] )
Adjusts the contrast of an image with a non-linear sigmoidal contrast algorithm. Increase the contrast of the image using a sigmoidal transfer function without saturating highlights or shadows. Contrast indicates how much to increase the contrast (0