// Assumes that f is no smaller than x.
func copyRealTo(f *rimg64.Image, x *fftw.Array2) {
for u := 0; u < f.Width; u++ {
for v := 0; v < f.Height; v++ {
f.Set(u, v, real(x.At(u, v)))
}
}
}
// Avoids f.Set(x, y, f.Get(x, y, ...)).
func addTo(f *rimg64.Image, x, y int, v float64) {
f.Set(x, y, f.At(x, y)+v)
}
