ValueError: could not broadcast input array from shape (256,340,3) into shape (256,340,30)

Question

I'm trying to save in python a stack of 10 rgb images, but i get the following error:

rgb[:,:,:, i] = img
ValueError: could not broadcast input array from shape (256,340,3) into shape (256,340,30) 

I tried:

img = cv2.imread(img_file, cv2.IMREAD_UNCHANGED)
rgb[:,:,:, i] = img

I also tried:

chunks = 10
step = int(math.floor((duration - chunks + 1)/(num_samples)))
dims = (256, 340, chunks * 3, num_samples)
rgb = np.zeros(shape=dims, dtype=np.float64)
   for i in range(num_samples):
    for j in range(chunks):
         img_file = os.path.join(vid_name, 'image_{0:04d}.jpg'.format(i*step+j+1 + start_frame))
         img = cv2.imread(img_file, cv2.IMREAD_UNCHANGED)
         img = cv2.resize(img, dims[1::-1])
         rgb[:,:,(j+1)*3, i] = img

img_file keeps the path to the image, it gets it correct. I've tested it with

print("%r") % img_file

What I want to achive is 10 stacked rgb images.

Any help is appreciated. Thank you!

Answer 1

Approach #1 : To make things simpler, I would suggest initializing a 5D array instead by splitting the second last axis into two axes, keeping chunks and 3 along them, like so -

dims = (256, 340, chunks , 3, num_samples)

To compensate for this edit, we need to make the assigning part of image into the output array inside the nested loops, like so -

rgb[:,:,j, :, i] = img

After performing all of those operations, at the end if needed, just reshape into 4D array -

rgb.shape = (256, 340, chunks* 3, num_samples)

So, in all three edits needed.

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Approach #2 : Keeping the loopy code from the question as it is, we could just do -

rgb[:,:,j*3:(j+1)*3, i] = img