Estimate Brightness of an image Opencv

Question

I have been trying to obtain the image brightness in Opencv, and so far I have used calcHist and considered the average of the histogram values. However, I feel this is not

Answer 1

I prefer Valentin's answer, but for 'yet another' way of determining average-per-pixel brightness, you can use numpy and a geometric mean instead of arithmetic. To me it has better results.

from numpy.linalg import norm

def brightness(img):
    if len(img.shape) == 3:
        # Colored RGB or BGR (*Do Not* use HSV images with this function)
        # create brightness with euclidean norm
        return np.average(norm(img, axis=2)) / np.sqrt(3)
    else:
        # Grayscale
        return np.average(img)