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If savefig() produces a blank image, first check whether the plotted artists are on the same Matplotlib Figure you save. Keep the handles returned by plt.subplots(), plot through the matching Axes, and call fig.savefig(...). Then check save order, transparency, output format and path, and cropping. The seven causes below are a practical debugging checklist, not an official Matplotlib classification.
Start by saving a known plot to the Figure you created
Matplotlib’s pyplot.savefig saves the current figure, while Figure.savefig saves the specific Figure whose method you call. In scripts with multiple figures, using an explicit handle avoids relying on whichever figure pyplot currently considers active.
import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([0, 1, 2], [0, 1, 4])
fig.savefig("plot.png", facecolor="white", transparent=False)This known-data example is a diagnostic pattern, not a claim that it has been run here. If it produces a visible plot, focus on the original code’s data, plotting branch, and Figure selection. If it does not, confirm the actual output path and inspect the file itself before changing rendering settings.
Check these seven causes in order
1. No visible artists were added
A plotting branch may not run, the input may be empty, or an earlier condition may skip the plotting call. Check the code path that supplies the data and verify the Axes has content—for example, inspect ax.lines for line plots and the relevant collections or images for other plot types. Try a small known-data plot to distinguish a data or control-flow problem from a save problem.
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2. The plot went to a different Axes or Figure
Mixing pyplot’s implicit current Axes with explicit Figure handles can make it less obvious where the plot was drawn. Keep the pair returned by plt.subplots() together: use ax.plot(...) or ax.imshow(...) to draw, then save with fig.savefig(...). This makes the intended destination explicit.
3. Pyplot saved a different current figure
plt.savefig(...) operates on the current figure. If your code creates several figures, the current one may not be the one containing the plot. Call savefig on the handle for the intended Figure instead: fig.savefig("plot.png").
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4. Saving happens before plotting is complete
Saving captures the Figure’s state at the time of the call. Check the order of operations and place the save after all plotting and annotation calls. A later call that adds artists cannot change a file that was already written.
5. Transparency or colors make the plot look blank
A transparent figure can blend into a viewer’s background, and foreground or background colors can have too little contrast. For a quick check, save an opaque version with a contrasting face color:
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fig.savefig("plot.png", facecolor="white", transparent=False)Also check the Figure and Axes colors, along with any transparent, facecolor, or edgecolor arguments passed to saving. Open the result against a contrasting background before concluding that it contains no content.
6. You are inspecting the wrong file or format
Confirm the output path, filename extension, explicit format argument, and application used to open the result. Matplotlib can infer a format from the extension; when a format is specified explicitly, that format is used. Available formats depend on the active backend, so an unexpected extension or incompatible reader can make the output seem wrong even when a file was saved.
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7. Cropping or bounds put the plot outside the saved region
bbox_inches controls the region included in the file. The value 'tight' asks Matplotlib to calculate a tight bounding box, and pad_inches adds padding when tight bounding-box saving is used. These settings address cropping or excess whitespace; they cannot create missing plotted content.
If a global tight-bounds setting may be responsible, remove it temporarily to diagnose. For clipped labels or unwanted whitespace, try:
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fig.savefig("plot.png", bbox_inches="tight", pad_inches=0.1)Use save settings only for the symptom they can fix
| Symptom | What to check or change | What the setting cannot do |
|---|---|---|
| No data appears or the wrong Figure was saved | Check that plotting ran, artists were added to the intended Axes, and the explicit Figure handle is saved. | dpi and bbox_inches cannot add artists or select the correct plot for you. |
| Labels are clipped or there is too much whitespace | Adjust layout or try bbox_inches="tight" with suitable pad_inches. |
A tight bounding box does not fix an empty Figure. |
| The output looks invisible against the viewer | Check transparency and Figure or Axes colors; try an opaque, contrasting face color. | Changing resolution does not resolve a foreground/background contrast problem. |
| The file behaves unexpectedly when opened | Check the path, extension, explicit format, backend-supported formats, and viewer. | A different filename alone does not prove the intended Figure was saved. |
| Rendering differs from expectations | Check the preceding issues first; consider the backend only if there is a specific format or compatibility reason. | Changing backends is not a general fix for missing plot content. |
When should you change the backend?
Usually, not as the first fix. Matplotlib’s savefig documentation says the default backend is normally sufficient. Check whether a specific output format or backend compatibility issue applies before changing it; first rule out an empty Figure, the wrong Figure handle, save order, transparency, and file selection.
Does calling show() clear the Figure before saving?
Do not assume that it always does. The Figure reference says Figure.show does not manage a GUI event loop and recommends pyplot.show() for a pure Python shell or script. That is event-loop guidance, not a universal rule that showing a Figure clears it before a later save. For predictable output, save the intended Figure handle at the point in your code where its plotted content is complete.
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