OpenCV TypeError: Expected cv::UMat for argument 'src' - What is this?

Question

Disclaimer: huge openCV noob

Traceback (most recent call last):

File \"lanes2.py\", line 22, in

canny = canny(lane_image)         


        

Answer 1

Is canny your own function? Do you use Canny from OpenCV inside it? If yes check if you feed suitable argument for Canny - first Canny argument should meet following criteria:

• type: <type 'numpy.ndarray'>
• dtype: dtype('uint8')
• being single channel or simplyfing: grayscale, that is 2D array, i.e. its shape should be 2-tuple of ints (tuple containing exactly 2 integers)

You can check it by printing respectively

type(variable_name)
variable_name.dtype
variable_name.shape

Replace variable_name with name of variable you feed as first argument to Canny.

Answer 2

I got round thid by writing/reading to a file. I guessed cv.imread would put it into the format it needed. This code for anki Vector SDK program but you get the idea.

tmpImage = robot.camera.latest_image.raw_image.save('temp.png')
pilImage = cv.imread('temp.png')

Answer 3

src is the first argument to cv2.cvtColor.

The error you are getting is because it is not the right form. cv2.Umat() is functionally equivalent to np.float32(), so your last line of code should read:

gray = cv2.cvtColor(np.float32(imgUMat), cv2.COLOR_RGB2GRAY)

Answer 4

Just add this at start: image = cv2.imread(image)

Answer 5

Not your code is the problem this is perfectly fine:

gray = cv2.cvtColor(imgUMat, cv2.COLOR_RGB2GRAY)

The problem is that imgUMat is None so you probably made a mistake when loading your image:

imgUMat = cv2.imread("your_image.jpg")

I suspect you just entered the wrong image path.

Answer 6

Sometimes I have this error when videostream from imutils package doesn't recognize frame or give an empty frame. In that case, solution will be figuring out why you have such a bad frame or use a standard VideoCapture(0) method from opencv2