OpenCV error - cv2.cvtcolor

Question

I am a newbie to openCV and I am stuck at this error with no resolution. I am trying to convert an image from BGR to grayscale format using this code-

img = cv2.         


        

Answer 1

imagine you have a function called preprocessing() that preprocess your images with cv2, if you try to apply it as:

data = np.array(list(map(preprocessing,data)))

it won't work and that because np.array creates int64and you are trying to assign np.uint8 to it, what you should do instead is adding dtype parameter as follow:

data = np.array(list(map(preprocessing,data)), dtype = np.uint8)

Answer 2

This is because your numpy array is not made up of the right data type. By default makes an array of type np.int64 (64 bit), however, cv2.cvtColor() requires 8 bit (np.uint8) or 16 bit (np.uint16). To correct this change your np.full() function to include the data type:

img = np.full((100,80,3), 12, np.uint8)

Answer 3

The error occured because the datatype of numpy array returned by cv2.imread is uint8, which is different from the datatype of numpy array returned by np.full(). To make the data-type as uint8, add the dtype parameter-

img = np.full((100,80,3), 12, dtype = np.uint8)
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

Answer 4

It may be easier to initialize new numpy array with initial image as source and dtype=np.uint8:

import numpy as np    
img = cv2.imread('path//to//image//file')    
img = np.array(img, dtype=np.uint8)
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)