(PECL imagick 2 >= 2.3.0, PECL imagick 3)
Imagick::getImageAlphaChannel — Checks if the image has an alpha channel
Returns whether the image has an alpha channel.
Questa funzione non contiene parametri.
Returns true if the image has an alpha channel value and false if not,
i.e. the image is RGB rather than RGBA
or CMYK rather than CMYKA.
Lancia una ImagickException in caso di errore.