I think you'll have a problem with BGR data absent ctypes, since you have a numpy array with the base pointing at the first red channel value, and you want an array with the base pointing 2 bytes before the first red channel value. This is almost definitely "unsafe"?.. or does numpy have functions knowing that due to the negative z stride, the red value before the blue value is within the bounds of the original array? I somehow doubt it though it would be very impressive. And I think the last A value is hopelessly out of reach absent ctypes since a safe API has no information that this last value is within the array bounds; more strictly speaking all the alpha values are out of bounds according to the shape and strides of the BGRA array.
