Image colormaps in Matplotlib

Introduction

Colormaps help us show images with colors that make patterns easy to see. They change how numbers in images look by using colors.

When you want to show a heatmap of temperatures in a city.

When you need to display grayscale images with colors to highlight details.

When visualizing data like elevation or intensity in a picture.

When you want to make scientific images easier to understand by using colors.

When comparing different images with consistent color schemes.

Syntax

Matplotlib

import matplotlib.pyplot as plt
plt.imshow(image_data, cmap='colormap_name')
plt.colorbar()
plt.show()

image_data is your image or 2D data array.

cmap sets the colormap by name, like 'gray', 'viridis', or 'hot'.

Examples

Shows the image in grayscale colors from black to white.

Matplotlib

plt.imshow(image_data, cmap='gray')
plt.colorbar()
plt.show()

Uses the 'viridis' colormap with blue to yellow colors, good for colorblind-friendly visuals.

Matplotlib

plt.imshow(image_data, cmap='viridis')
plt.colorbar()
plt.show()

Displays the image with colors from black to red to yellow, like heat intensity.

Matplotlib

plt.imshow(image_data, cmap='hot')
plt.colorbar()
plt.show()

Sample Program

This code creates a simple 10x10 gradient image and shows it using the 'viridis' colormap. The colorbar shows how colors map to values.

Matplotlib

import numpy as np
import matplotlib.pyplot as plt

# Create a 2D array with a gradient
image_data = np.linspace(0, 1, 100).reshape(10, 10)

# Show image with 'viridis' colormap
plt.imshow(image_data, cmap='viridis')
plt.colorbar()
plt.title('Image with Viridis Colormap')
plt.show()

Important Notes

Colormaps can be sequential, diverging, or qualitative depending on your data.

Use plt.colorbar() to add a color scale next to your image.

Try different colormaps to find the best one for your data story.

Summary

Colormaps change how image data values show as colors.

Use cmap in plt.imshow() to pick a colormap.

Adding a colorbar helps explain the color meaning.