im.apply: Apply Function Pixelwise to List of Images
Returns a pixel image obtained by applying a function
to the values of corresponding pixels in several pixel images.
im.apply(X, FUN, ...)
A list of pixel images (objects of class "im").
A function that can be applied to vectors,
or a character string giving the name of such a function.
Additional arguments to FUN.
A pixel image (object of class "im").
The argument X should be a list of pixel images
(objects of class "im"). If the images do not have
identical pixel grids, they will be converted to a common
grid using harmonise.im.
At each pixel location, the values of the images in X
at that pixel will be extracted as a vector. The function
FUN will be applied to this vector. The result (which should be
a single value) becomes the pixel value of the resulting image.