如何在 OpenCV Python 中检测全黑色图像？

Question

I want to write code in python to print a text when the input image is perfectly black and no other colors are present in it. Which are the functions to be used?

Answer 1

Try this:

# open the file with opencv
image = cv2.imread("image.jpg", 0)
if cv2.countNonZero(image) == 0:
    print "Image is black"
else:
    print "Colored image"

You basically check if all pixel values are 0 (black).

Answer 2

image = cv2.imread("image.jpg", 0)
if cv2.countNonZero(image) == 0:
    print "Image is black"
else:
    print "Colored image"

The snippet above provided by @ebeneditos it's a good ideia but in my tests opencv returns an assertion error when capturing a colored image.

According opencv community , countNonZero() can handle only single channel images . Thus, one simple solution would be to convert the image to grayscale before counting the pixels. Here it is:

gray_version = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
if cv2.countNonZero(gray_version) == 0:
    print("Error")
else:
    print("Image is fine")