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Upscaling the grayscale image in Python

In this article, we will see how to upscale the greyscale image using image processing in Python?
Submitted by Ankit Rai, on June 02, 2019

Upscaling of an image refers to enlarging the size of an image.

In this program, we will be using two functions of OpenCV-python (cv2) module.. let's see their syntax and descriptions first

1) imread():
It takes an absolute path/relative path of your image file as an argument and returns its corresponding image matrix.

If flag value is:

• 1: Loads a color image.
• 0: Loads image in grayscale mode.
• -1: Loads image as such including alpha channel.

If the flag value is not given then show the original image, which path is given.

2) imshow():
It takes window name and image matrix as an argument in order to display an image in a display window with a specified window name.

Also In this program, we will be using one function of numpy module.

median(): It takes array and returns the median of the array .

Also, in this program we are using the concept of array slicing

Let, A is 1-d array:
A[start:stop:step]

1. start: Starting number of the sequence.
2. stop: Generate numbers up to, but not including this number.
3. step: Difference between each number in the sequence.

Example:

    A = [1,2,3,4,5,6,7,8,9,10]
    print(A[ 1: 5])

    Output:
    [2,3,4,5]

Python program for upscaling the grayscale image in Python

# open-cv library is installed as cv2 in python
# import cv2 library into this program
import cv2

# import numpy as np name
import numpy as np

# read an image using imread() function of cv2
# we have to  pass only the path of the image
img = cv2.imread(r'C:/Users/user/Desktop/pic6.jpg',0)

# displaying the image using imshow() function of cv2
# In this : 1st argument is name of the frame
# 2nd argument is the image matrix
cv2.imshow('original image',img)

# upscaling code

# Upscaling the image x,y times along row and column
x,y = 2, 2

# here image is of class 'uint8', the range of values  
# that each colour component can have is [0 - 255]

# create a zero matrix of order of x,y times
# of previous image of 3-dimensions
upscale_img = np.zeros((x*img.shape[0],y*img.shape[1]),np.uint8)

i, m = 0, 0

while m < img.shape[0] :

    j, n = 0, 0
    while n < img.shape[1]:

        # We assign pixel value from original image matrix to the
        # new upscaling image matrix in alternate rows and columns
        upscale_img[i, j] = img[m, n]

        # increment j by y times
        j += y

        # increment n by one
        n += 1

    # increment m by one
    m += 1

    # increment i by x times
    i += x
   
cv2.imshow('upscaling image',upscale_img)

Output