input - An array of images from which the output image is to
output - An output image to be generated from the input. This
method does not change the output image.
An integer array of the same dimension as one plane of the output
image. Each element of the array gives the index of the input image
that should be used to get the value of that point. A value -2 indicates
that there is no suitable input image. A value -3 indicates that
the output pixel is not physical (e.g., it lies outside the valid region
in the projection plane). Zero and positive values give the appropriate indices.