This command computes, for each possible distance \(r\),
the average pixel value of the pixels lying at
distance \(r\) from the origin. Kernel smoothing is used
to obtain a smooth function of \(r\).

If `result="fv"`

(the default) the result is a function
object of class `"fv"`

giving the mean pixel value of `X`

as a function of distance from the origin.

If `result="im"`

the result is a pixel image, with the same
dimensions as `X`

, giving the mean value of `X`

over all pixels lying at the same distance from the origin
as the current pixel.

If `padzero=TRUE`

(the default), the value of `X`

is assumed to be zero outside the window of `X`

. The rotational
mean at a given distance \(r\) is the average value of the image
`X`

over the *entire* circle of radius \(r\),
including zero values outside the window if the circle
lies partly outside the window.

If `padzero=FALSE`

, the value of `X`

is taken to be
undefined outside the window of `X`

. The rotational mean
is the average of the `X`

values over the *subset* of the circle
of radius \(r\) that lies entirely inside the window.