Image rotation and zoom in SciPy - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of rotated image shape

What is the shape of the image after rotating a 100x100 array by 45 degrees using scipy.ndimage.rotate with reshape=True?

SciPy

import numpy as np
from scipy.ndimage import rotate

image = np.ones((100, 100))
rotated = rotate(image, 45, reshape=True)
print(rotated.shape)

A (142, 142)

B (100, 100)

C (120, 120)

D (141, 141)

💡 Hint

Think about how rotating a square by 45 degrees increases the bounding box size.

Rotating a 100x100 image by 45 degrees with reshape=True expands the output shape to fit the entire rotated image. The new shape is approximately 142x142 due to the diagonal length.

❓ data_output

intermediate

Zoomed image pixel value at center

Given a 5x5 image with all zeros except the center pixel set to 1, what is the pixel value at the center after zooming by 2 using scipy.ndimage.zoom?

SciPy

import numpy as np
from scipy.ndimage import zoom

image = np.zeros((5,5))
image[2,2] = 1
zoomed = zoom(image, 2)
center_value = zoomed[5,5]
print(round(center_value, 2))

A 1.0

B 0.5

C 0.25

D 0.0

💡 Hint

Zooming uses interpolation which spreads the pixel value.

Zooming by 2 doubles the image size and interpolates pixel values. The center pixel value reduces to about 0.5 due to interpolation smoothing.

🔧 Debug

advanced

Identify error in rotation code

What error does the following code raise? import numpy as np from scipy.ndimage import rotate image = np.ones((50, 50)) rotated = rotate(image, '90') print(rotated.shape)

SciPy

import numpy as np
from scipy.ndimage import rotate
image = np.ones((50, 50))
rotated = rotate(image, '90')
print(rotated.shape)

A TypeError: an integer is required

B ValueError: invalid literal for int() with base 10: '90'

C TypeError: unsupported operand type(s) for -: 'str' and 'int'

D No error, prints (50, 50)

💡 Hint

Check the type of the angle argument passed to rotate.

The rotate function expects a numeric angle, but a string '90' was passed, causing a TypeError.

❓ visualization

advanced

Effect of zoom factor on image size

If you zoom a 64x64 image by a factor of 1.5 using scipy.ndimage.zoom, what will be the shape of the resulting image?

SciPy

import numpy as np
from scipy.ndimage import zoom
image = np.zeros((64,64))
zoomed = zoom(image, 1.5)
print(zoomed.shape)

A (96, 96)

B (95, 95)

C (96, 95)

D (95, 96)

💡 Hint

Zoom rounds the output shape to the nearest integer.

Zooming 64 by 1.5 gives 96, and scipy.ndimage.zoom rounds the output shape to (96, 96).

🚀 Application

expert

Combining rotation and zoom effects

You have a 128x128 image. You first rotate it by 30 degrees with reshape=False, then zoom it by 0.5. What is the shape of the final image?

SciPy

import numpy as np
from scipy.ndimage import rotate, zoom
image = np.ones((128,128))
rotated = rotate(image, 30, reshape=False)
final = zoom(rotated, 0.5)
print(final.shape)

A (63, 63)

B (128, 128)

C (65, 65)

D (64, 64)

💡 Hint

reshape=False keeps the shape same after rotation; zoom scales down by half rounding to nearest integer.

Rotation with reshape=False keeps shape (128,128). Zoom by 0.5 scales to 64 (128*0.5), and scipy.ndimage.zoom output shape is rounded to nearest integer, resulting in (64,64).