@Nikronic
It seems that I cannot make it work. I have to use a method to turn one channel of grayscale image to 3 channel (RGB).I thought I have managed it with CV but I had problems with the normalize function. I used:

image = Image.open(img_name + ‘.png’).convert(‘RGB’)

but then it raises other shape related errors.
Do you think there is an error at the above code instead use CV?