Display multiple images in subplots

Question

How do I use the matlib function plt.imshow(image) to display multiple images?

For example my code is as follows:

for file in images:
    process(file)

def process(filename):
    image = mpimg.imread(filename)
    <something gets done here>
    plt.imshow(image)

My results show that only the last processed image is shown effectively overwriting the other images

Answer 1

You can set up a framework to show multiple images using the following:

import matplotlib.pyplot as plt
import matplotlib.image as mpimg

def process(filename: str=None) -> None:
    """
    View multiple images stored in files, stacking vertically

    Arguments:
        filename: str - path to filename containing image
    """
    image = mpimg.imread(filename)
    # <something gets done here>
    plt.figure()
    plt.imshow(image)

for file in images:
    process(file)

This will stack the images vertically

Answer 2

Building on Aadhar Bhatt's answer:

from matplotlib.image import imread
import matplotlib.pyplot as plt

v_slice = [] #create an empty list called v_slice
for i in range(0,4):
    image = imread("test.png") #Here I load the same image 4 times-replace this  with code that generates images
    v_slice.append(image)


#Aadhar Bhatt's answer
plt.figure()
#subplot(r,c) provide the no. of rows and columns
f, axarr = plt.subplots(4,1) 
# use the created array to output your multiple images. In this case I have stacked 4 images vertically
axarr[0].imshow(v_slice[0])
axarr[1].imshow(v_slice[1])
axarr[2].imshow(v_slice[2])
axarr[3].imshow(v_slice[3])

Answer 3

Using a plt.show() after plt.imshow(image) while in the for loop worked for me.

for file in images:
    process(file)
    
def process(filename):
    image = mpimg.imread(filename)
    # <something gets done here>
    plt.imshow(image)
    plt.show()

Answer 4

To display the multiple images use subplot()

plt.figure()

#subplot(r,c) provide the no. of rows and columns
f, axarr = plt.subplots(4,1) 

# use the created array to output your multiple images. In this case I have stacked 4 images vertically
axarr[0].imshow(v_slice[0])
axarr[1].imshow(v_slice[1])
axarr[2].imshow(v_slice[2])
axarr[3].imshow(v_slice[3])

Answer 5

In first instance, load the image from file into a numpy matrix

from typing import Union,List
import numpy
import cv2
import os
def load_image(image: Union[str, numpy.ndarray]) -> numpy.ndarray:
    # Image provided ad string, loading from file ..
    if isinstance(image, str):
        # Checking if the file exist
        if not os.path.isfile(image):
            print("File {} does not exist!".format(imageA))
            return None
        # Reading image as numpy matrix in gray scale (image, color_param)
        return cv2.imread(image, 0)

    # Image alredy loaded
    elif isinstance(image, numpy.ndarray):
        return image

    # Format not recognized
    else:
        print("Unrecognized format: {}".format(type(image)))
        print("Unrecognized format: {}".format(image))
    return None

Then you can plot multiple image using the following method:

import matplotlib.pyplot as plt
def show_images(images: List[numpy.ndarray]) -> None:
    n: int = len(images)
    f = plt.figure()
    for i in range(n):
        # Debug, plot figure
        f.add_subplot(1, n, i + 1)
        plt.imshow(images[i])

    plt.show(block=True)

The show_images method take in input a list of images that you can read iteratively using the load_image method.