(PECL imagick 2.0.0)
Imagick::contrastStretchImage — Enhances the contrast of a color image
$black_point
   , float $white_point
   [, int $channel = Imagick::CHANNEL_ALL
  ] )Enhances the contrast of a color image by adjusting the pixels color to span the entire range of colors available. This method is available if Imagick has been compiled against ImageMagick version 6.2.9 or newer.
black_point
     The black point.
white_point
     The white point.
channel
     
       Provide any channel constant that is valid for your channel mode. To
       apply to more than one channel, combine channeltype constants using
       bitwise operators. Imagick::CHANNEL_ALL. Refer to this
       list of  channel constants.
      
   Returns TRUE on success.