write_videofile writes blank black when writing grayscale

[ROZBEH]

Hi there,

I am trying to use moviepy's fl_image functionality and apply a function to each image frame and then save it back. The whole process finishes successfully but the output video is just pure black. Does anyone know why does this happen? I here post part of the code.

def processing(input_frame):
    image = input_frame
    gradx = abs_sobel_thresh(image, orient='x', sobel_kernel=ksize, thresh=(20, 100))
    grady = abs_sobel_thresh(image, orient='y', sobel_kernel=ksize, thresh=(20, 100))
    mag_binary = mag_thresh(image, sobel_kernel=ksize, mag_thresh=(30, 100))
    dir_binary = dir_threshold(image, sobel_kernel=ksize, thresh=(0.6, 1.3))
    color_binary = color_channel(image)
    combined_grad = np.zeros_like(dir_binary)
    combined_grad[((gradx == 1) & (grady == 1)) | ((mag_binary == 1) & (dir_binary == 1))] = 1
    combined_binary = np.zeros_like(dir_binary)
    combined_binary[(combined_grad == 1) | (color_binary == 1)] = 1
    combined_binaries.append(combined_binary)
    kernel = np.ones((3,3),np.uint8)
    opening = cv2.morphologyEx(combined_binary, cv2.MORPH_OPEN, kernel)
    opening = cv2.morphologyEx(opening, cv2.MORPH_CLOSE, kernel)
    return opening


write_output = 'project_video_out.mp4'
clip = VideoFileClip("project_video.mp4")
video_clip = clip.fl_image(processing)
video_clip.write_videofile(write_output)

Specifications

• Python Version: 3.5
• Moviepy Version: '0.2.3.2'
• Platform Name: Mac OSX
• Platform Version: 10.14

[ROZBEH]

The problem was solving by converting the image back to the Image format with the following commands.

opening = Image.fromarray(opening * 255)
opening = np.asarray(opening)