python - Failure to use adaptiveThreshold: CV_8UC1 in function adaptiveThreshold

Question

I have used openCV python and encountered an error.

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

plt.subplot(1,1,1),plt.imshow(img_thresh_Gaussian, cmap = 'gray')
plt.title("Image"), plt.xticks([]), plt.yticks([])
plt.show()

but I received:

cv2.error: /home/phuong/opencv_src/opencv/modules/imgproc/src/thresh.cpp:1280: error: (-215) src.type() == CV_8UC1 in function adaptiveThreshold

Do I have to install something else?

Answer 1

The problem is that you are trying to use adaptive thresholding to an image that is not in greyscale. And the function only works with a greyscale images.

So you have to convert your image to a greyscale format as it is described in documentation.

They read the image in a greyscale format with: img = cv2.imread('dave.jpg',0). You can also convert it to greyscale with: img_grey = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)