The ImageMagick function 'getImageChannelStatistics' returns an array of arrays. The first array has keys with values set to 0, 1, 2, 4, 8, and 32. Each of these arrays, in turn, has five values, mean, minima, maxima, standard deviation, and depth. A sample print_r of the array produces...
 => Array
[mean] => 0
[minima] => 1.0E+37
[maxima] => -1.0E-37
[standardDeviation] => 0
[depth] => 1
 => Array
[mean] => 13215.2836185
[minima] => 0
[maxima] => 65535
[standardDeviation] => 19099.2202751
[depth] => 8
What does each 0, 1, 2, etc., value mean for the keys? Those are shared, evaluated values of the ImageMagick Channel Constants. You have the channel constant values that look like imagick::CHANNEL_UNDEFINED, with "_VALUE" values of: undefined, red, gray, cyan, green, magenta, blue, yellow, alpha, opacity, matte, black, index, all, and default. If you actually print out these constants, you get '0' for undefined, '1' for red, gray, and cyan, '2' for green and magenta, '4' for blue and yellow, and '8' for alpha, opacity, and matte, or '32' for black and index. Why do multiple channels share the same evaluated integer values? That's because they're colors from different color spaces, with Red/Green/Blue being the RGB spectrum, Cyan/Magenta/Yellow/blacK being the CMYK spectrum, etc., etc.. If you want to get the statistical result values for Cyan or Red, you'll be accessing the same channel keys.
There are five values produced for each color channel. The element values for the keys 'mean' and 'standardDeviation' are the results from the getImageChannelMean function. The element values for the keys 'minima' and 'maxima' are the results from the getChannelRange function. And the element values for the key 'depth' is the result from the getImageChannelDepth function. All of these values can be useful in terms of measuring the Channel values of a particular image.
And now, some sample code :
$imagick_type = new Imagick();
$file_to_grab_with_location = "image_workshop_directory/test.bmp";
$file_handle_for_viewing_image_file = fopen($file_to_grab_with_location, 'a+');
$imagick_type_channel_statistics = $imagick_type->getImageChannelStatistics();