Basically the montage width should be.... (geometry_size + 2*frame_size) * images_per_row
+ geometry_offset * (images_per_row + 1)
The height is similar but with extra spacing for labels and the optional montage title. Shadow does not have any effect in the current versions of montage though years ago it did.
There has been a proposal for some method by which a final montage size can also be specified.
See http://www.imagemagick.org/Usage/bugs/f ... ntage_size
The other parameters (not defined) would then be adjusted accordingly. However figuring out how the various options should interact when things are not defined, is a complex issue as it has not been done with a specified final output size in mind.
If someone would like to re-program montage (it is quite a straight forward IM application program) to do this, I am sure users would love you, and worship you for your great programming skills.
