(PECL imagick 2, PECL imagick 3)
Imagick::getImageChannelExtrema — Gets the extrema for one or more image channels
此函数在 Imagick 3.4.4 中被 废弃，强烈建议不要应用此函数。
Gets the extrema for one or more image channels. Return value is an associative array with the keys "minima" and "maxima".
channelProvide any channel constant that is valid for your channel mode. To apply to more than one channel, combine channeltype constants using bitwise operators. Refer to this list of channel constants.
成功时返回 true。
错误时抛出 ImagickException。