thumbnails make terrible canvas prints

import numpy as np
import scipy.ndimage as ndimage
import matplotlib.image as mpimg 
import matplotlib.pyplot as plt
import cv2

img = mpimg.imread('img.jpg')
plt.imshow(img);

img.shape

big_img = ndimage.zoom(img, (2,2,1))   #first two numbers of tuple are zoom factor (for x and y)

big_img.shape

plt.imshow(big_img)

kernel1 = np.array([[0, -1, 0], 
                   [-1, 5, -1], 
                   [0, -1, 0]])

kernel2 = np.array([[-1, -1, -1],
                    [-1, 9, -1],
                    [-1, -1, -1]])


# Sharpen image
sharpened = cv2.filter2D(big_img, -1, kernel2)   # choose which kernel

f, (ax1, ax2) = plt.subplots(1, 2, figsize=(14,9))
ax1.imshow(big_img)
ax1.set_title('original')
ax2.imshow(sharpened)
ax2.set_title('sharpened, kernel2');