python - 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)

File "lanes2.py", line 5, in canny

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

TypeError: Expected cv::UMat for argument 'src'

What exactly is 'src' referring to?

Answer 1

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 2

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

UMat is a part of the Transparent API (TAPI) than help to write one code for the CPU and OpenCL implementations.

Answer 3

The following can be used from numpy:

import numpy as np 
image = np.array(image)

Answer 4

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 5

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 6

This is a general error, which throws sometimes, when you have mismatch between the types of the data you use. E.g I tried to resize the image with opencv, it gave the same error. Here is a discussion about it.

Answer 7

Some dtype are not supported by specific OpenCV functions. For example inputs of dtype np.uint32 create this error. Try to convert the input to a supported dtype (e.g. np.int32 or np.float32)

Answer 8

Just add this at start:

image = cv2.imread(image)

Answer 9

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

Answer 10

that is referring to the expected dtype of your image
"image".astype('float32') should solve your issue

Answer 11

If using ImageGrab

Verify that your image is not a 0x0 area due to an incorrect bbox.

Answer 12

Verify the application root folder is the same as the file you are attempting to run.

Answer 13

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')