The getQuantumDepth works much like the other "Depth" functions and much like the getQuantumRange function. Like the Depth functions, it returns a value indicating the number of bits to store the unique color values -- 16-bit = 2^16 unique colors, which is 65,535 (counting starts at '0' in binary, as opposed to '1' in decimal). Like the getQuantumRange function, it returns an array with two values, one being a long integer ('quantumDepthLong') and the other being a string ('quantumDepthLong'). The only difference, besides the variable types, is that the string version has a 'Q' prefixed to it.
Here's some sample code and the results, given a color, BMP file photograph that is 600x450 pixels...
<?php
$imagick_type = new Imagick();
$file_to_grab = "image_workshop_directory/test.bmp";
$file_handle_for_viewing_image_file = fopen($file_to_grab, 'a+');
$imagick_type->readImageFile($file_handle_for_viewing_image_file);
$imagick_type_quantum_depth = $imagick_type->getQuantumDepth();
print("<pre>");
print_r($imagick_type_quantum_depth);
print("</pre>");
?>
Output:
Array
(
[quantumDepthLong] => 16
[quantumDepthString] => Q16
)