pub fn pixel_diff_summary<I, J, P>(actual: &I, expected: &J) -> Option<String>
where
    P: Pixel + PartialEq,
    P::Subpixel: fmt::Debug,
    I: GenericImage<Pixel = P>,
    J: GenericImage<Pixel = P>,
{
    significant_pixel_diff_summary(actual, expected, |p, q| p != q)
}
Human readable description of some of the pixels that differ
between left and right, or None if all pixels match.
src/utils.rs