# I need help for my assignment (in python)

I have an assignent where i need to recreate the nearest neighbor interpolation function from scratch in python.
I just started the language a few days ago so i’m trying to write every little steps to achieve that.

This is my first try to solve it The reasoning behind it is (for a given image and a scale of 0.5 for example) to scale the positions X and Y of the original image to X’ and Y’ like this:

Shape of the given image : 10x10.
I want to scale it to 5x5 (this is a downscaling)

X and Y positions before scaling

X=[0,1,2,3,4,5,6,7,8,9]
Y=[0,1,2,3,4,5,6,7,8,9]

X and Y positions after scaling

X’=[0,2.25,4.5,6.75,9]
Y’=[0,2.25,4.5,6.75,9]

rounded

X’=[0,2,5,7,9]
Y’=[0,2,5,7,9]

Then i look up the pixels from the original image using those positions

I dont know if this make sense or i’m missing something

My code
(the way i named my variables is not so great)

``````def interpolation_nn(image, scale):

# saving the type of the image
dtype = image.dtype

# Calculation of the size of the original image and of the interpolated image
#Original img
height,width = img.shape

#interpolated image
Scaled_width = np.floor(width * scale)
Scaled_height = np.floor(height * scale)

# Calculation of pixel coordinates in the interpolated image
Scaled_X_coordinates=np.linspace(0.0, width, num=Scaled_width)
Scaled_Y_coordinates=np.linspace(0.0, height, num=Scaled_height)

#rounding my positions
Scaled_X_coordinates=np.around(Scaled_X_coordinates)
Scaled_Y_coordinates=np.around(Scaled_Y_coordinates)
sys.stdout.write("Scaled_X_coordinates:"+str(Scaled_X_coordinates)+"\n")
sys.stdout.write("Scaled_Y_coordinates:"+str(Scaled_Y_coordinates)+"\n")

#edited
finalMatrix=[]
for Column in Scaled_X_coordinates.astype(int) :
for Line in Scaled_Y_coordinates.astype(int) :
Scaled_column = [image[Line-1,Column-1]]
finalMatrix.append( Scaled_column )
#transfrom my array into an image
finalMatrix = Image.fromarray(finalMatrix)
#Does not work

#returning a new matrix with the same type as the given img
return finalMatrix.astype(dtype)

``````

I have no idea how to look up into the pixels of the original image to recreate the new one having the new scaled positions. If something is unclear, please ask:)

The best way to achieve this is to use cv2 (OpenCV library). Look up cv2.resize().

``````import cv2
import numpy as np

def interpolation(image, scale):

width = int(image.shape * scale / 100)
height = int(image.shape * scale / 100)
dimensions = (width, height)

resized = cv2.resize(image, dimensions, cv2.INTER_AREA)

cv2.imshow('Scaled Image', resized)
cv2.waitKey()
cv2.destroyAllWindows()