Image extent and aspect ratio in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of image with extent and aspect set to 'auto'

What will be the shape of the displayed image when using extent=[0, 4, 0, 2] and aspect='auto' in matplotlib's imshow?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

img = np.array([[1, 2], [3, 4]])
plt.imshow(img, extent=[0, 4, 0, 2], aspect='auto')
plt.axis('on')
plt.show()

A The image will stretch to fill the rectangle from x=0 to 4 and y=0 to 2, ignoring the original pixel aspect ratio.

B The image will keep square pixels and fit within the extent, possibly leaving empty space.

C The image will not display because aspect='auto' is invalid.

D The image will be distorted to a square shape regardless of extent values.

💡 Hint

Think about how 'aspect=auto' affects image scaling inside the given extent.

Setting aspect='auto' allows the image to stretch to fill the entire extent rectangle, ignoring the original pixel aspect ratio. This means the image shape on the plot matches the extent dimensions exactly.

❓ Predict Output

intermediate

Effect of aspect='equal' with extent on image display

What happens when you set aspect='equal' and extent=[0, 4, 0, 2] in matplotlib's imshow for a 2x2 image?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

img = np.array([[1, 2], [3, 4]])
plt.imshow(img, extent=[0, 4, 0, 2], aspect='equal')
plt.axis('on')
plt.show()

A The image pixels will be square, so the image will not fill the entire extent rectangle, leaving extra space.

B The image will stretch to fill the extent rectangle, distorting pixel shapes.

C The image will be clipped and only part of it will show.

D The image will flip vertically due to aspect='equal'.

💡 Hint

Consider what 'aspect=equal' means for pixel shape and how it interacts with extent size.

With aspect='equal', matplotlib keeps pixels square. Since the extent rectangle is wider than tall (4 units wide, 2 units tall), the image will not stretch to fill it fully. Instead, it fits with square pixels, leaving empty space.

❓ visualization

advanced

Visualize difference between aspect='auto' and aspect='equal'

Which option shows the correct matplotlib code to plot the same 3x2 image twice side by side, left with aspect='auto' and right with aspect='equal', both using extent=[0,6,0,4]?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

img = np.arange(6).reshape(3, 2)
fig, axs = plt.subplots(1, 2, figsize=(10, 5))

# Left plot
axs[0].imshow(img, extent=[0, 6, 0, 4], aspect='auto')
axs[0].set_title('aspect=auto')

# Right plot
axs[1].imshow(img, extent=[0, 6, 0, 4], aspect='equal')
axs[1].set_title('aspect=equal')

plt.show()

A Both images keep pixel shape, but the left image is clipped.

B Both images stretch to fill the 6x4 area, ignoring pixel shape.

C The left image stretches to fill the 6x4 area; the right image keeps pixel shape, leaving space.

D The left image is flipped horizontally; the right image is flipped vertically.

💡 Hint

Recall how aspect='auto' and aspect='equal' affect image scaling.

The left image with aspect='auto' stretches to fill the entire extent area, distorting pixels. The right image with aspect='equal' keeps pixels square, so it fits inside the extent without distortion, leaving empty space.

🔧 Debug

advanced

Identify the error in image extent usage

What error occurs when running this code snippet? import matplotlib.pyplot as plt import numpy as np img = np.ones((3,3)) plt.imshow(img, extent=[0, 2, 3]) plt.show()

Matplotlib

import matplotlib.pyplot as plt
import numpy as np
img = np.ones((3,3))
plt.imshow(img, extent=[0, 2, 3])
plt.show()

A TypeError: 'extent' must be a tuple, not list

B ValueError: 'extent' must be a sequence of length 4

C No error, image displays normally

D IndexError: list index out of range

💡 Hint

Check the length of the extent parameter.

The extent parameter must have exactly 4 values: [xmin, xmax, ymin, ymax]. Here, only 3 values are given, causing a ValueError.

🚀 Application

expert

Calculate displayed image width in data units with aspect='equal'

Given a 4x2 pixel image displayed with extent=[0, 8, 0, 4] and aspect='equal', what is the width in data units of one pixel on the x-axis?

A 0.5 units

B 1 unit

C 4 units

D 2 units

💡 Hint

With aspect='equal', pixels are square. Use extent and image shape to find pixel size.

The extent width is 8 units and the image has 4 pixels horizontally. With aspect='equal', pixels are square, so each pixel is 8/4 = 2 units wide.