split_dng.py

import rawpy
import imageio

raw = rawpy.imread('RAW_2017_12_12_22_08_32_701.dng')

print(raw.raw_image.shape)
# (3032, 4032)


def save_plane(plane, name):
    # Dumb tone-mapping. (The raw file is 16 bit, but we can only display 8 bits).
    plane //= 2

    # Clamp to 0-255.
    plane[plane > 255] = 255
    plane = plane.astype('uint8')

    imageio.imsave(name, plane)

# Save each of the four image planes as a separate png.
save_plane(raw.raw_image[::2, ::2], '0.png')
save_plane(raw.raw_image[::2, 1::2], '1.png')
save_plane(raw.raw_image[1::2, ::2], '2.png')
save_plane(raw.raw_image[1::2, 1::2], '3.png')