Why export quality matters in Matplotlib - Challenge Your Understanding

Challenge - 5 Problems

❓ visualization

intermediate

What happens when you export a plot with low DPI?

Consider a matplotlib plot exported with a low DPI (dots per inch) setting. What is the most likely visible effect on the saved image?

Matplotlib

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

A The plot lines become thicker automatically.

B The image file size is very large and detailed.

C The image appears blurry or pixelated when zoomed in.

D The colors of the plot change to grayscale.

💡 Hint

Think about what DPI controls in an image.

Low DPI means fewer dots per inch, so the image has less detail and looks blurry or pixelated when enlarged.

❓ Predict Output

intermediate

What is the file size difference when exporting with different DPI?

Given the following code snippets, which saved image will likely have the larger file size?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('plot.png', dpi=300)  # High DPI
plt.savefig('plot_low.png', dpi=50)  # Low DPI

A plot.png will have a larger file size than plot_low.png.

B plot_low.png will have a larger file size than plot.png.

C Both files will have the same size because the plot is the same.

D File size depends only on the file format, not DPI.

💡 Hint

Higher DPI means more pixels to store.

Higher DPI images contain more pixels, increasing file size compared to lower DPI images.

🔧 Debug

advanced

Why does this exported plot look blurry despite high DPI?

Look at this code that exports a plot with dpi=300, but the saved image looks blurry. What is the most likely cause?

Matplotlib

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

A The plot window was resized before saving, causing distortion.

B The image viewer is zoomed in, making the image appear blurry.

C The plot was saved before any data was plotted.

D The dpi parameter only affects screen display, not saved files.

💡 Hint

Think about how image viewers display images.

Zooming in on an image in a viewer can make even high DPI images appear blurry due to pixel enlargement.

🧠 Conceptual

advanced

Why use vector formats for exporting plots?

Which is the main advantage of exporting plots as vector graphics (e.g., SVG, PDF) instead of raster images (e.g., PNG)?

A Vector graphics support more colors than raster images.

B Vector graphics are easier to edit pixel by pixel.

C Vector graphics files are always smaller than raster images.

D Vector graphics scale without losing quality, unlike raster images.

💡 Hint

Think about what happens when you zoom in on different image types.

Vector graphics use shapes and lines, so they can be scaled infinitely without blurring.

❓ data_output

expert

How many pixels does a 6x4 inch plot have when exported at 200 DPI?

If you export a plot sized 6 inches wide and 4 inches tall at 200 DPI, how many total pixels does the image contain?

A 960,000 pixels

B 48,000 pixels

C 1,200 pixels

D 12,000 pixels

💡 Hint

Calculate width_pixels = width_in_inches * DPI, height_pixels = height_in_inches * DPI, then multiply.

Width pixels = 6 * 200 = 1200, height pixels = 4 * 200 = 800, total pixels = 1200 * 800 = 960,000.