cv2.error: OpenCV(4.1.2) /Users/travis/build/skvark/opencv-python/opencv/modules/imgproc/src/hough.cpp:471: error: (-215:Assertion failed) image.type() == CV_8UC1 in function 'HoughLinesProbabilistic' code example

Example: (-215:Assertion failed) img.type() == CV_8UC1 in func

img_blur = cv2.medianBlur(self.cropped_img,5).astype('uint8')
img_thresh_Gaussian = cv2.adaptiveThreshold(img_blur, 255, cv2.ADAPTIVE_THRESH_GAUSSIAN_C, cv2.THRESH_BINARY, 11, 2)