alignment reference.
Images in a stack will usually vary in scale and position. All other
images are resized and rotated to match with this image. This also
determines the scale of the output image, which is important for
performing measurements. By default middle image of the stack is
used as reference.</dd>
<dt><code>--global-align</code></dt>
<dd>By default each image is aligned against its neighbour. This
improves results in deep stacks, as blur at the extreme focus levels
can make direct alignment to r