Checking pixel color in OpenCV with Python

Question

I am currently working on a project with python and OpenCV. For one part of the project, I would like to check and see if one specific pixel (specifically the pixel with coordinate 100, 100) is not equal to the color black. My code is as follows.

import cv2

img = cv2.imread('/Documents/2016.jpg')

if img[100, 100] != [0, 0, 0]:
    print("the pixel is not black")

When I go and fun in the terminal I get this error.

File "/Documents/imCam.py", line 5, in <module>
if img[100, 100] != [0, 0, 0]:
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

What am I doing wrong?

s1hofmann · Accepted Answer · 2016-02-16 23:34:13Z

2

As it states, you're comparing lists with multiply entries, which is too unprecise.

You'll have to use numpy.any like

import cv2
import numpy as np

img = cv2.imread('/Documents/2016.jpg')

if np.any(img[100, 100] != 0):
    print("the pixel is not black")

edited Feb 16, 2016 at 23:34

answered Feb 16, 2016 at 18:26

s1hofmann

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2 Comments

Tyler Abair Over a year ago

Doesn't this solution only work for colors that have the same value for all of B, G, and R? How could you compare to a different color? Like if img[100, 100] != [222, 12, 127]:

s1hofmann Over a year ago

img[100, 100] != [222, 12, 127] returns a list of booleans, np.all() returns True iff each element of a given list is True. So np.all(img[100, 100] == [222, 12, 127]) will check if both colors match.

Andrii Abramov · Accepted Answer · 2021-03-16 19:59:12Z

0

import cv2

image = cv2.imread('abc.jpg')

if image[50, 50, 0] != 0:
    print("the pixel is not black")

Try this :)

edited Mar 16, 2021 at 19:59

Andrii Abramov

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answered Jul 30, 2019 at 7:19

Kumar S

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