Matplotlib RGB Channels Visualization

Introduction

Matplotlib is a popular data visualization library in Python. It provides various plotting tools, including 2D and 3D plotting capabilities. In this tutorial, we will use the RGBAxes module of the AxesGrid toolkit in Matplotlib to display RGB channels.

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Import necessary libraries

In this step, we will import the necessary libraries: numpy, matplotlib.pyplot, and mpl_toolkits.axes_grid1.axes_rgb.

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1.axes_rgb import RGBAxes, make_rgb_axes

Define a function to get RGB channels

In this step, we will define a function get_rgb() to get the R, G, and B channels of an image. In this example, we will use the get_sample_data() function of the cbook module to get a sample image.

import matplotlib.cbook as cbook

def get_rgb():
    ## Get a sample image
    Z = cbook.get_sample_data("axes_grid/bivariate_normal.npy")
    Z[Z < 0] = 0.
    Z = Z / Z.max()

    ## Get R, G, and B channels
    R = Z[:13, :13]
    G = Z[2:, 2:]
    B = Z[:13, 2:]

    return R, G, B

Define a function to create a RGB cube

In this step, we will define a function make_cube() to create a RGB cube from the R, G, and B channels obtained in the previous step. The function will return the R, G, and B cubes, as well as the RGB image.

def make_cube(r, g, b):
    ## Get the shape of R
    ny, nx = r.shape

    ## Create the R, G, and B cubes
    R = np.zeros((ny, nx, 3))
    R[:, :, 0] = r
    G = np.zeros_like(R)
    G[:, :, 1] = g
    B = np.zeros_like(R)
    B[:, :, 2] = b

    ## Combine the R, G, and B cubes to create the RGB image
    RGB = R + G + B

    return R, G, B, RGB

Create a RGBAxes plot

In this step, we will create a RGBAxes plot using the RGBAxes class. We will use the imshow_rgb() method of the RGBAxes object to display the RGB image.

def demo_rgb1():
    ## Create a figure and a RGBAxes object
    fig = plt.figure()
    ax = RGBAxes(fig, [0.1, 0.1, 0.8, 0.8], pad=0.0)

    ## Get the R, G, and B channels
    r, g, b = get_rgb()

    ## Display the RGB image using the imshow_rgb() method
    ax.imshow_rgb(r, g, b)

Create a RGBAxes plot with separate channels

In this step, we will create a RGBAxes plot with separate channels using the make_rgb_axes() function. We will use the imshow() method of the Axes objects to display the R, G, and B channels.

def demo_rgb2():
    ## Create a figure and an Axes object
    fig, ax = plt.subplots()

    ## Create the R, G, and B Axes objects using the make_rgb_axes() function
    ax_r, ax_g, ax_b = make_rgb_axes(ax, pad=0.02)

    ## Get the R, G, and B channels and create the RGB cube
    r, g, b = get_rgb()
    im_r, im_g, im_b, im_rgb = make_cube(r, g, b)

    ## Display the RGB image and the R, G, and B channels
    ax.imshow(im_rgb)
    ax_r.imshow(im_r)
    ax_g.imshow(im_g)
    ax_b.imshow(im_b)

    ## Set the tick parameters and spine colors for all Axes objects
    for ax in fig.axes:
        ax.tick_params(direction='in', color='w')
        ax.spines[:].set_color("w")

Display the plots

In this step, we will call the demo_rgb1() and demo_rgb2() functions to create the plots and display them using the plt.show() function.

demo_rgb1()
demo_rgb2()

plt.show()

Summary

In this tutorial, we have learned how to use the RGBAxes module of the AxesGrid toolkit in Matplotlib to display RGB channels. We have covered the following steps:

1. Import necessary libraries
2. Define a function to get RGB channels
3. Define a function to create a RGB cube
4. Create a RGBAxes plot
5. Create a RGBAxes plot with separate channels
6. Display the plots.