List of all colors in an image using opencv and python

Question

Python beginner here. I'm using python 3.6 and opencv and I'm trying to create a list of rgb values of all colors present in an image. I can read the rgb values of one pixel using cv2.imread followed by image[px,px]. The result is a numpy array. What I want is list of rgb tuples of unique colors present in an image and am not sure how to do that. Any help is appreciated. TIA

Have you tried the naive aproach of just looping over the whole image and collecting every unique color (i.e. keep a list/dict/whatever with every color seen so far) — FlyingTeller
I wasn't sure how to convert from array to tuple and I just searched and apparantly tuple(a) where a is array gives tuple lol (forgive me, I just started learning python). So, I'm trying the looping approach now. Meanwhile, it'd be great if someone could share a better approach since I have to loop it over 3000 images and it may take a long time. — Kalyan M

iR0Nic iR0Nic · Accepted Answer · 2018-08-06T10:19:21

Check out numpy's numpy.unique() function:

import numpy as np

test = np.array([[255,233,200], [23,66,122], [0,0,123], [233,200,255], [23,66,122]])
print(np.unique(test, axis=0, return_counts = True))

>>> (array([[  0,   0, 123],
       [ 23,  66, 122],
       [233, 200, 255],
       [255, 233, 200]]), array([1, 2, 1, 1]))

You can collect the RGB numpy arrays in a 2D numpy array and then use the numpy.unique() funtion with the axis=0 parameter to traverse the arrays within. Optional parameter return_counts=True will also give you the number of occurences.

List of all colors in an image using opencv and python

1 Answers