For each line that is to be added to the image, a set of 5 values
follow the keyword ADD. These 5 values are:
1 The value added to all pixels on the line. (positive or negative)
2 The line number of the first end point.
3 The sample number of the first end point.
4 The line number of the other end point.
5 The sample number of the other end point.
Up to 25 sets of 5 values may follow the ADD keyword. End points may be
specified in any order.