Color segmentation:

Color segmentation is a method to separate out objects from the image based on its different color intensities from other objects in the image.

Color space:

RGB:

The most commonly used color space is RGB( Red, Green, Blue ) which is also known as additive color space as these primary colors can add up with different intensities to produce different colors.

HSV:

HSV stands for  Hue, Saturation and Brightness. It is used to define contrast in the image, hence it is more localized in nature. 

Let us compare the localization of an image in both color space:

Implemented code in Python:

#import required librabies
import cv2
import matplotlib.pyplot as plt
import numpy as np
from mpl_toolkits.mplot3d import Axes3D
from matplotlib import cm
from matplotlib import colors

flower1 = cv2.imread('dahlia.jpg');

#visualization in RGB color space
b, g, r = cv2.split(flower1); #bydefault openCV reads image in bgr format
fig = plt.figure();
axis = fig.add_subplot(1, 1, 1, projection="3d"); #for 3D projection

#normalization
color = flower1.reshape((np.shape(flower1)[0]*np.shape(flower1)[1], 3));
norm = colors.Normalize(vmin=-1,vmax=1);
norm.autoscale(color);
color = norm(color).tolist();

axis.scatter(b.flatten(), g.flatten(), r.flatten(), facecolors=color, marker=".");
axis.set_xlabel("Blue");
axis.set_ylabel("Green");
axis.set_zlabel("Red");
plt.show();

#visulization in HSV color space
flower2 = cv2.cvtColor(flower1, cv2.COLOR_RGB2HSV);
h, s, v = cv2.split(flower2);
fig = plt.figure();
axis = fig.add_subplot(1, 1, 1, projection="3d");

axis.scatter(h.flatten(), s.flatten(), v.flatten(), facecolors=color, marker=".");
axis.set_xlabel("Hue");
axis.set_ylabel("Saturation");
axis.set_zlabel("Value");
plt.show();

OUTPUT:

Color segmentation process:

1. Define range of color to be segmented( thresholding ).
2. Create a mask according to the threshold values.
3. Perform masking on the image using AND operation.

Implemented code in Python:

import cv2 
import numpy as np 

flower = cv2.imread('dahlia.jpg',1);

#conversion of BGR color space to HSV color space 
hsv = cv2.cvtColor(flower, cv2.COLOR_BGR2HSV);
	
#step1: thresholding
lower = np.array([0, 30, 0]);
upper = np.array([200, 200, 200]);

#step2: masking 
mask = cv2.inRange(hsv, lower, upper); 
	
output_img = cv2.bitwise_and(flower, flower, mask = mask);

cv2.imshow('Original', flower); 
cv2.imshow('Applied mask', mask); 
cv2.imshow('Output', output_img); 
	
#wait for 10 sec
cv2.waitKey(10000); 
cv2.destroyAllWindows();

OUTPUT:

Thank you Rishika Gupta for this article.