Figure size and DPI in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of figure size and DPI settings

What is the size in pixels of the figure created by this code?

Matplotlib

import matplotlib.pyplot as plt
fig = plt.figure(figsize=(4, 3), dpi=100)
width, height = fig.get_size_inches() * fig.dpi
print(int(width), int(height))

A 400 300

B 4 3

C 100 75

D 40 30

💡 Hint

Remember that figure size is in inches and DPI means dots per inch.

The figure size is 4 inches by 3 inches. DPI is 100 dots per inch. So pixels = inches * DPI = 4*100=400 and 3*100=300.

❓ data_output

intermediate

DataFrame shape after resizing figure

Given this code, what is the shape of the DataFrame after plotting?

Matplotlib

import pandas as pd
import matplotlib.pyplot as plt

data = {'x': range(5), 'y': [10, 20, 15, 25, 30]}
df = pd.DataFrame(data)
fig, ax = plt.subplots(figsize=(6, 4), dpi=80)
df.plot(x='x', y='y', ax=ax)
print(df.shape)

A (5, 2)

B (6, 4)

C (80, 60)

D (4, 6)

💡 Hint

The DataFrame shape is independent of figure size.

The DataFrame has 5 rows and 2 columns, so shape is (5, 2). Figure size does not change data shape.

❓ visualization

advanced

Effect of DPI on saved image resolution

Which saved image will have the highest resolution (most pixels)?

Matplotlib

import matplotlib.pyplot as plt
fig1 = plt.figure(figsize=(5, 4), dpi=80)
fig1.savefig('image1.png')
fig2 = plt.figure(figsize=(5, 4), dpi=200)
fig2.savefig('image2.png')

A image1.png has higher resolution

B Resolution depends only on figsize, not dpi

C Both images have the same resolution

D image2.png has higher resolution

💡 Hint

DPI means dots per inch, so higher DPI means more pixels.

Both images have the same size in inches, but image2.png has dpi=200, so it has more pixels and higher resolution.

🧠 Conceptual

advanced

Understanding figure size and DPI relationship

If you double the DPI but keep the figure size the same, what happens to the image?

A The image becomes larger in inches

B The image has more pixels and looks sharper

C The image size and quality stay the same

D The image becomes smaller in pixels

💡 Hint

Think about what DPI controls in an image.

Doubling DPI increases pixels per inch, so the image has more pixels and looks sharper at the same physical size.

🔧 Debug

expert

Why does this saved figure look blurry?

This code saves a figure but the image looks blurry. What is the main cause?

Matplotlib

import matplotlib.pyplot as plt
fig = plt.figure(figsize=(3, 2), dpi=50)
plt.plot([1, 2, 3], [4, 5, 6])
fig.savefig('blurry.png')

A The plot command is missing labels

B The figsize is too large, causing blur

C The dpi is too low, causing low pixel resolution

D The savefig filename is incorrect

💡 Hint

Low DPI means fewer pixels in the image.

DPI of 50 is low, so the saved image has few pixels and looks blurry when viewed at normal size.