Vector vs raster output decision in Matplotlib - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Output format of matplotlib savefig with vector format

What type of file is produced by this code snippet?

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('output.svg')

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('output.svg')

A A plain text file with raw data points

B A vector image file (paths and shapes) like SVG

C A raster image file (pixels) like PNG or JPEG

D A binary executable file

💡 Hint

SVG files store images as shapes and lines, not pixels.

Saving as 'output.svg' produces a vector image file. Vector files store shapes and lines, so they scale without losing quality.

❓ Predict Output

intermediate

Effect of dpi on raster output in matplotlib

What happens when you save a plot as a PNG with dpi=300 compared to dpi=72?

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('high_res.png', dpi=300)
plt.savefig('low_res.png', dpi=72)

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('high_res.png', dpi=300)
plt.savefig('low_res.png', dpi=72)

A The low_res.png will have more pixels than high_res.png

B Both files will have the same pixel dimensions and quality

C The high_res.png will have more pixels and better detail than low_res.png

D The dpi setting only affects vector files, not PNG

💡 Hint

DPI means dots per inch, affecting pixel density in raster images.

Higher dpi means more pixels per inch, so the image is sharper and larger in pixel dimensions.

❓ data_output

advanced

Comparing file sizes of vector vs raster outputs

Given a plot saved as 'plot.svg' (vector) and 'plot.png' (raster), which statement about their file sizes is generally true for complex plots?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np
x = np.linspace(0, 10, 1000)
y = np.sin(x)
plt.plot(x, y)
plt.savefig('plot.svg')
plt.savefig('plot.png')

A The PNG file is usually smaller than the SVG for complex plots

B File size depends only on image resolution, not format

C Both files have the same size regardless of plot complexity

D The SVG file is usually smaller than the PNG for complex plots

💡 Hint

Vector files store instructions for shapes, which can grow with complexity.

For complex plots with many points, vector files can become very large because they store every shape and line, while raster files store pixels and can be compressed.

🧠 Conceptual

advanced

Choosing output format for publication-quality figures

Which output format is best for figures that need to be scaled to any size without losing quality in a scientific paper?

A Vector formats like PDF or SVG

B Raster formats like PNG or JPEG

C Plain text files with raw data

D Bitmap formats like BMP

💡 Hint

Think about scaling images without pixelation.

Vector formats store shapes and lines mathematically, so they scale perfectly without losing quality, ideal for publication.

🔧 Debug

expert

Why does saving a plot as PNG with dpi=100 produce a blurry image?

A user saves a matplotlib plot as PNG with dpi=100 but the image looks blurry when zoomed in. Which option explains the cause?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('blurry.png', dpi=100)

A The dpi setting only affects screen display, not saved files

B PNG format is vector and does not support dpi settings

C The plot data is incorrect causing blurriness

D The dpi is too low, resulting in fewer pixels and less detail

💡 Hint

DPI controls pixel density in raster images.

Low dpi means fewer pixels per inch, so the image looks blurry when zoomed or printed large.

Practice

1. Which type of output should you choose in matplotlib for a chart that needs to stay sharp when zoomed in or printed in large size?

easy

A. Raster output

B. No output is needed

C. Both vector and raster output

D. Vector output

Solution

1. Step 1: Understand output types

   Vector output uses lines and shapes that scale without losing quality, ideal for charts.

2. Step 2: Match output to use case

   Charts need to stay sharp when zoomed or printed large, so vector is best.

3. Final Answer:

   Vector output -> Option D

4. Quick Check:

   Sharp scalable graphics = Vector output [OK]

Hint: Choose vector for sharp, scalable images like charts [OK]

Common Mistakes:

• Choosing raster output for charts
• Thinking both outputs are always needed
• Confusing vector with raster images

2. Which file extension in matplotlib will produce a raster output file?

easy

A. .svg

B. .png

C. .pdf

D. .eps

Solution

1. Step 1: Identify raster file extensions

   Raster images are pixel-based; common extensions include .png, .jpg, .bmp.

2. Step 2: Match extension to output type

   .png is a raster format, while .svg, .pdf, and .eps are vector formats.

3. Final Answer:

   .png -> Option B

4. Quick Check:

   Raster output = .png [OK]

Hint: Raster files often end with .png or .jpg [OK]

Common Mistakes:

• Choosing .svg as raster
• Confusing .pdf as raster
• Not knowing file extension types

3. What will be the output type of the following matplotlib savefig command?

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('output.pdf')

medium

A. Raster image file

B. No file saved

C. Vector image file

D. Text file

Solution

1. Step 1: Check file extension in savefig

   The file is saved as 'output.pdf', which is a vector format.

2. Step 2: Understand matplotlib output choice

   Matplotlib chooses vector output for .pdf files automatically.

3. Final Answer:

   Vector image file -> Option C

4. Quick Check:

   PDF extension = Vector output [OK]

Hint: File extension determines vector or raster output [OK]

Common Mistakes:

• Assuming .pdf is raster
• Thinking no file is saved
• Confusing output type with plot type

4. You want to save a detailed photo using matplotlib but accidentally use plt.savefig('photo.svg'). What is the main problem with this?

medium

A. SVG is a vector format and may not handle photo details well

B. SVG files are always corrupted

C. Matplotlib will save a raster image inside SVG

D. No file will be saved

Solution

1. Step 1: Understand SVG format

   SVG is vector-based, best for shapes and lines, not detailed photos.

2. Step 2: Recognize photo detail needs

   Photos have many colors and pixels; vector formats can't represent them well.

3. Final Answer:

   SVG is a vector format and may not handle photo details well -> Option A

4. Quick Check:

   Photo detail needs raster, SVG is vector [OK]

Hint: Use raster formats for photos, not vector like SVG [OK]

Common Mistakes:

• Thinking SVG files are corrupted
• Expecting raster inside SVG
• Assuming no file is saved

5. You have a matplotlib plot with both a detailed photo background and vector line plots on top. Which approach best preserves quality when saving the figure?

hard

A. Save as a raster image like .png to capture photo details

B. Save as a vector image like .pdf to keep lines sharp

C. Save two separate files: photo as raster and lines as vector

D. Save as .svg and expect both photo and lines to be perfect

Solution

1. Step 1: Analyze image components

   The photo background needs raster to keep details; vector lines alone won't capture photo well.

2. Step 2: Choose output that preserves all parts

   Saving as raster (.png) keeps photo details and acceptable line quality.

3. Step 3: Consider alternatives

   Saving separate files is complex; .svg won't handle photo well.

4. Final Answer:

   Save as a raster image like .png to capture photo details -> Option A

5. Quick Check:

   Photo + lines = raster output best [OK]

Hint: For photos with lines, raster (.png) keeps all details [OK]

Common Mistakes:

• Choosing vector only and losing photo quality
• Trying to save both in one vector file
• Ignoring photo detail needs