Apply a non-linear warp to the image, where the warp is specified by a
dense flow field of offset vectors that define the correspondences of
pixel values in the output image back to locations in the source image.
Specifically, the pixel value at output[b, j, i, c] is
images[b, j - flow[b, j, i, 0], i - flow[b, j, i, 1], c].
The locations specified by this formula do not necessarily map to an int
index. Therefore, the pixel value is obtained by bilinear
interpolation of the 4 nearest pixels around
(b, j - flow[b, j, i, 0], i - flow[b, j, i, 1]). For locations outside
of the image, we use the nearest pixel values at the image boundary.
4-D float Tensor with shape [batch, height, width, channels].
A 4-D float Tensor with shape [batch, height, width, 2].