output = (const*file1*file2) / (div)
Note that a 32 bit integer buffer is used for each pixel. However the input and output data are written as 16 bit signed integers. To multiply by a non-integral quantity, one must use both constand div.
The box switch restricts the range of the division to the area of the image(s) inside the specified box.
The resultant image is written into file1.fts unless overridden by the outfile option