(PECL imagick 2.0.0)
Applies an expression to an image
bool Imagick::evaluateImage ( int $op, float $constant [, int $channel = Imagick::CHANNEL_ALL ] )
Applys an arithmetic, relational, or logical expression to an image. Use these operators to lighten or darken an image, to increase or decrease contrast in an image, or to produce the "negative" of an image.
Parameters:
op