Saving Figures¶

Exporting figures to files is essential for reports, papers, and presentations.

Basic savefig¶

Save using the Figure object:

```python import matplotlib.pyplot as plt import numpy as np

x = np.linspace(0, 2*np.pi, 100) y = np.sin(x)

fig, ax = plt.subplots() ax.plot(x, y)

fig.savefig("sine_wave.png") ```

Or via pyplot:

python plt.savefig("sine_wave.png")

File Formats¶

Common formats and their use cases:

python fig.savefig("plot.png") fig.savefig("plot.pdf") fig.savefig("plot.svg")

Resolution (DPI)¶

Control resolution with the dpi parameter:

```python import matplotlib.pyplot as plt import numpy as np

x = np.linspace(-2, 2, 1000) y1 = np.cos(40 * x) y2 = np.exp(-x**2)

fig = plt.figure(figsize=(8, 2.5), facecolor="#f1f1f1") ax = fig.add_axes((0.1, 0.1, 0.8, 0.8), facecolor="#e1e1e1")

ax.plot(x, y1 * y2) ax.plot(x, y2, 'g') ax.set_xlabel("x") ax.set_ylabel("y")

Higher DPI = larger file, better quality¶

fig.savefig("graph_lowres.png", dpi=72) fig.savefig("graph_highres.png", dpi=300) ```

DPI guidelines:

• Screen: 72-100 dpi
• Print: 300 dpi
• Publication: 300-600 dpi

Background Options¶

Control background appearance:

```python

White background (default)¶

fig.savefig("plot.png")

Custom background color¶

fig.savefig("plot.png", facecolor="#f1f1f1")

Transparent background¶

fig.savefig("plot.png", transparent=True)

Edge color¶

fig.savefig("plot.png", edgecolor='black') ```

Bounding Box¶

Control what portion of the figure is saved:

```python

Tight bounding box (removes whitespace)¶

fig.savefig("plot.png", bbox_inches='tight')

Add padding around tight box¶

fig.savefig("plot.png", bbox_inches='tight', pad_inches=0.1) ```

Complete Example¶

```python import matplotlib.pyplot as plt import numpy as np

x = np.linspace(-2np.pi, 2np.pi, 100) y_sin = np.sin(x) y_cos = np.cos(x)

fig, ax = plt.subplots(figsize=(10, 4)) ax.plot(x, y_sin, label='sin(x)') ax.plot(x, y_cos, label='cos(x)') ax.set_xlabel('x') ax.set_ylabel('y') ax.set_title('Trigonometric Functions') ax.legend() ax.grid(True, alpha=0.3)

Save with all options¶

fig.savefig( "trig_functions.png", dpi=300, bbox_inches='tight', pad_inches=0.1, facecolor='white', transparent=False )

plt.show() ```

Saving Multiple Formats¶

Save the same figure in multiple formats:

```python import matplotlib.pyplot as plt import numpy as np

fig, ax = plt.subplots() ax.plot([1, 2, 3, 4])

for fmt in ['png', 'pdf', 'svg']: fig.savefig(f"output.{fmt}", dpi=300, bbox_inches='tight') ```

Best Practices¶

1. Use vector formats for print: PDF or SVG scale without quality loss
2. Use PNG for web/screen: Good quality, universal support
3. Set DPI before plotting: fig = plt.figure(dpi=300)
4. Use bbox_inches='tight': Removes unwanted whitespace
5. Be consistent: Use the same settings across all figures in a document

Key Takeaways¶

• Use fig.savefig() to export figures
• Choose format based on use case (PNG for screen, PDF for print)
• Higher DPI means better quality but larger files
• Use bbox_inches='tight' to remove whitespace
• Use transparent=True for overlay graphics

Exercises¶

Exercise 1. Write code that creates a simple plot and saves it to a PNG file with dpi=200 and a tight bounding box. Use fig.savefig().

Exercise 2. Explain the difference between saving a figure as PNG versus SVG. When would you choose each format?

Exercise 3. Write code that saves the same figure in three formats (PNG, PDF, SVG) by calling fig.savefig() three times with different file extensions. Set dpi=150 for the raster format.

Exercise 4. Create a figure with a transparent background by passing transparent=True to savefig(). Explain why this is useful when embedding plots in presentations.

Exercise 5. A colleague's saved figure has clipped axis labels and low resolution. Diagnose and fix: write a savefig call that (a) prevents clipping, (b) sets print-quality DPI, (c) uses vector format for a journal submission, and (d) embeds fonts. Explain each parameter choice.