Mastering OpenCV 4 with Python

Grayscale histograms with a mask

To see how to apply a mask, see the grayscale_histogram_mask.py script, where a mask is created and used to calculate a histogram by using the previously created mask. In order to create the mask, the following line is necessary:

mask = np.zeros(gray_image.shape[:2], np.uint8)mask[30:190, 30:190] = 255

Therefore, the mask consists of a black image with the same dimensions as the loaded image, and with the white ones corresponding to the regions where we want to calculate the histogram.

Afterwards, the cv2.calcHist() function is called passing the created mask:

hist_mask = cv2.calcHist([gray_image], [0], mask, [256], [0, 256])

The output of this script can be seen in the following screenshot:

As you can see, ...