Shooting .raw pictures with PiCamera - results in scrambled black and white images

Question

I'm trying to shoot some .raw pictures and I'd like to test both the rgb and the yuv option.

What I've obtained so far is a not usable file/image. Meaning that once I open the it with Photoshop, for example, I can only see a scrambled black and white image.

Here's the code using 'rgb':

import time
import picamera
campic = 1

def take_picture(campic):
    print("Take picture", campic)
    filename = "/home/pi/insect" + str(campic) + ".raw"

    with picamera.PiCamera() as camera:
        camera.resolution = (1920, 1088)
        camera.start_preview()
        time.sleep(2)
        camera.capture(filename, 'rgb')
        time.sleep(0.5)
        camera.stop_preview()

for i in range(3): # starting with 3 pics to try

    take_picture(campic)
    time.sleep(5)
    campic = campic + 1

Any idea on how to fix it would be greatly appreciated, thanks! :)