Python, RGB color comparisons

Question

I have a pixel from an OpenCV image with the RGB format in [r,g,b]. I would like to run a test so that if i find a color darker than [150,150,150] i stop a for loop.

This is what I have so far:

def test():
    for l in range(y, y+h):
        for d in range(x, x+w):
            print(image[l,d][0])
            if image[l,d] <= [150,150,150]:
                return;
            image[l,d] = [0,0,0]

Doesn't work though. Any ideas?

`if all(item <= 150 for item in image[l, d]):`. Does this work? — roganjosh, Aug 12 '17 at 13:25
Here are some related topics: https://stackoverflow.com/questions/13052857/comparing-two-lists-using-the-greater-than-or-less-than-operator and https://stackoverflow.com/questions/9254897/how-to-compare-all-items-in-a-list-with-an-integer-without-using-for-loop — chrki, Aug 12 '17 at 13:28
The pixel value is a numpy array. Hence something like `if np.all(image[l,d] <= [150,150,150]): ...` will do. — Dan Mašek, Aug 12 '17 at 13:36

score 3 · Answer 1 · answered Aug 12 '17 at 13:43

Since OpenCV images in Python are represented as numpy arrays, each pixel value will also be a numpy array. That means that the comparison operation will be vectorized, and return an array of boolean values, for example

>>> image[l,d] <= [150,150,150]
array([ True,  True,  True], dtype=bool)

Now, you want to check that the condition is satisfied for all the item pairs. That's where numpy.all comes into play.

>>> np.all(image[l,d] <= [150,150,150])
True

In fact, numpy arrays have a member method all(), which does the same thing.

>>> (image[l,d] <= [150,150,150]).all()
True

Python, RGB color comparisons

1 Answers1