Life's a garden. Dig it.
Challenge¶
Here's a grayscale image of a hand-written four from the MNIST dataset.
import numpy as np
arr = np.array(
[[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 50, 224, 0, 0, 0, 0, 0, 0, 0, 70, 29, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 121, 231, 0, 0, 0, 0, 0, 0, 0, 148, 168, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 195, 231, 0, 0, 0, 0, 0, 0, 0, 96, 210, 11, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 69, 252, 134, 0, 0, 0, 0, 0, 0, 0, 114, 252, 21, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 45, 236, 217, 12, 0, 0, 0, 0, 0, 0, 0, 192, 252, 21, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 168, 247, 53, 0, 0, 0, 0, 0, 0, 0, 18, 255, 253, 21, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 84, 242, 211, 0, 0, 0, 0, 0, 0, 0, 0, 141, 253, 189, 5, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 169, 252, 106, 0, 0, 0, 0, 0, 0, 0, 32, 232, 250, 66, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 15, 225, 252, 0, 0, 0, 0, 0, 0, 0, 0, 134, 252, 211, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 22, 252, 164, 0, 0, 0, 0, 0, 0, 0, 0, 169, 252, 167, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 9, 204, 209, 18, 0, 0, 0, 0, 0, 0, 22, 253, 253, 107, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 169, 252, 199, 85, 85, 85, 85, 129, 164, 195, 252, 252, 106, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 41, 170, 245, 252, 252, 252, 252, 232, 231, 251, 252, 252, 9, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 49, 84, 84, 84, 84, 0, 0, 161, 252, 252, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 127, 252, 252, 45, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 128, 253, 253, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 127, 252, 252, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 135, 252, 244, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 232, 236, 111, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 179, 66, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]]
)Modify the array so that the image flips across the horizontal centerline.
Solution¶
Flipping an object is one example of an affine transformation. There are multiple ways to do it, but a simple technique (implemented below) is to index arr with an array that selects the last row first, the second-to-last row second, and so on.
import numpy as np
import matplotlib.pyplot as plt
flipped = arr[np.arange(27,-1,-1)]
plt.imshow(
X=flipped,
vmin=0,
vmax=255,
interpolation='none',
cmap='gray',
)