array Imagick::compareImageChannels    ( Imagick $image   , int $channelType   , int $metricType   )

Imagick::compareImageChannelsReturns the difference in one or more images

image

Imagick object containing the image to compare.

channelType

Provide 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.

metricType

One of the metric type constants.