Get the Dominant Colors of an Image with K-Means

The logic

Most images are an RGB array where we can easily apply K-Means Clustering. The Centers of each cluster would be the most dominant colors of the image

Load the Image

We will load the image by using the matplotlib.image and then we will create a Pandas Data Frame of three columns, Red, Green Blue by iterating over image pixels.

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import seaborn as sns
import matplotlib.image as img
from scipy.cluster.vq import kmeans, vq
%matplotlib inline 

image =img.imread("landscape_1.jpeg")

image.shape
 

(700, 1050, 3)

plt.imshow(image)

r = []
g = []
b = []

for row in image:
    for pixel in row:
        # A pixel contains RGB values
        r.append(pixel[0])
        g.append(pixel[1])
        b.append(pixel[2])

df = pd.DataFrame({'red':r, 'green':g, 'blue':b})

df.head()
 

Elbow Method

Now we will apply the Elbow Method to find the number of K clusters.

distortions = []
num_clusters = range(1, 7)

# Create a list of distortions from the kmeans function
for i in num_clusters:
    cluster_centers, distortion = kmeans(df[['red','green','blue']].values.astype(float), i)
    distortions.append(distortion)

# Create a data frame with two lists - num_clusters, distortions
elbow_plot = pd.DataFrame({'num_clusters': num_clusters, 'distortions': distortions})

# Creat a line plot of num_clusters and distortions
sns.lineplot(x='num_clusters', y='distortions', data = elbow_plot)
plt.xticks(num_clusters)
plt.show()
 

As we can see from the plot, the number of clusters K=2

K-Means and Dominant Colors

The dominant colors are the cluster centers. Let’s get them:

cluster_centers, _ = kmeans(df[['red','green','blue']].values.astype(float), 2)
cluster_centers
 

array([[173.85432863, 136.00392373,  79.91006256],
       [223.40796294, 224.50774782, 224.42501677]])

We need to reshape them to \(1\times k \times 3\) where k is the number of clusters.

plt.imshow(cluster_centers.reshape(1,2,3)/255.)
 

As we can see, we get the dominant colors with few lines of code!

NB: In case we want to get the cluster labels we apply the vq function with inputs the data that we want to get the cluster labels and the cluster centers.

# Assign cluster labels
df['clusters'] = vq(df, cluster_centers)[0]
 

Want to learn more?

If you found this post helpful, you can have a look at other related posts:

• How to define a custom distance function for your clustering
• Hierarchical Clustering in Python
• K-Means Elbow Method in Python
• Hierarchical Clustering of Countries based on Eurovision Votes
• Most Dominant Color of an Image