c b | a b c d | c b a`)
        The input is extended by reflecting about the center of the last
        pixel. This mode is also sometimes referred to as whole-sample
        symmetric.

    'grid-wrap' (`a b c d | a b c d | a b c d`)
        The input is extended by wrapping around to the opposite edge.

    'wrap' (`d b c d | a b c d | b c a b`)
        The input is extended by wrapping around to the opposite edge, but in a
        way such that the last point and initial point exactly overlap. In this
        case it is not well defined which sample will be chosen at the point of
        overlap.z