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Imagick::setImageAlphaChannel — Sets image alpha channel
$mode
   )
   Activate or deactivate image alpha channel. The mode 
   is one of the Imagick::ALPHACHANNEL_* constants.
   This method is available if Imagick has been compiled against ImageMagick version 6.3.8 or newer.
  
mode
       One of the Imagick::ALPHACHANNEL_* constants
      
   Returns TRUE on success.
  
Throws ImagickException on error.