import numpy
cimport c_numpy
def negative_grayscale_image(c_numpy.ndarray img):
if img.nd != 2:
raise ValueError("Array is not 2-dimensional")
if img.dtype != numpy.dtype(numpy.uint8):
raise ValueError("Array does not contain numpy.uint8 elements")
cdef int di, dj, i, j
di = arr.strides[0] / sizeof(c_numpy.npy_uint8)
dj = arr.strides[1] / sizeof(c_numpy.npy_uint8)
cdef c_numpy.npy_uint8* buf = <c_numpy.npy_uint8*>img.data
for i in range(arr.dimensions[0]):
for j in range(arr.dimensions[1]):
buf[i * di + j * dj] = 255 - buf[i * di + j * dj] 