Setting Background Color to Transparent in Plotly Plots

Plotly is a versatile charting library that allows for extensive customization. One common requirement is to make the background of a plot transparent, which is particularly useful when embedding plots on websites with custom backgrounds or when layering plots. See how to set both the plot area and the overall figure background to transparent in Plotly.

Understanding Plotly Backgrounds

In Plotly, there are two main background properties you’ll typically interact with:

• plot_bgcolor: Controls the background color of the actual plotting area (where your data traces are drawn).
• paper_bgcolor: Controls the background color of the entire figure, including the margins, titles, and legend area.

To make a background transparent, you typically set its color to 'rgba(0,0,0,0)'. The ‘a’ in ‘rgba’ stands for alpha, which controls opacity (0 for fully transparent, 1 for fully opaque).

1. Making the Plot Area Background Transparent (plot_bgcolor)

This affects only the inner region where the data is plotted, leaving the margins and titles with the default background (usually white).

import plotly.graph_objects as go

fig = go.Figure(data=go.Scatter(x=[1, 2, 3], y=[4, 1, 2]))

fig.update_layout(
    title_text="Transparent Plot Area",
    plot_bgcolor='rgba(0,0,0,0)' # Set plot area background to transparent
)

fig.show()

2. Making the Entire Figure Background Transparent (paper_bgcolor)

This affects the background of the entire figure, including the plot area, margins, titles, and legend. If you only set paper_bgcolor to transparent, the plot_bgcolor will still default to opaque white unless also specified.

import plotly.graph_objects as go

fig = go.Figure(data=go.Scatter(x=[1, 2, 3], y=[4, 1, 2]))

fig.update_layout(
    title_text="Transparent Paper Background",
    paper_bgcolor='rgba(0,0,0,0)' # Set entire figure background to transparent
)

fig.show()

3. Making Both Plot Area and Figure Background Transparent

For a fully transparent plot that can be overlaid on any background, you should set both properties to transparent.

import plotly.graph_objects as go

fig = go.Figure(data=go.Scatter(x=[1, 2, 3], y=[4, 1, 2]))

fig.update_layout(
    title_text="Fully Transparent Plot",
    plot_bgcolor='rgba(0,0,0,0)',  # Transparent plot area
    paper_bgcolor='rgba(0,0,0,0)'   # Transparent overall figure background
)

fig.show()

4. Transparency for Specific Elements (e.g., Legend Background)

You can also set the background of other elements, like the legend, to transparent using similar rgba values.

import plotly.graph_objects as go

fig = go.Figure()
fig.add_trace(go.Scatter(x=[1, 2, 3], y=[4, 1, 2], name='Series A'))
fig.add_trace(go.Scatter(x=[1, 2, 3], y=[2, 3, 5], name='Series B'))

fig.update_layout(
    title_text="Transparent Legend Background",
    plot_bgcolor='rgba(0,0,0,0)',
    paper_bgcolor='rgba(0,0,0,0)',
    legend=dict(
        bgcolor='rgba(0,0,0,0)', # Transparent legend background
        bordercolor='rgba(0,0,0,0)' # Remove legend border if desired
    )
)

fig.show()

Key Points

• Use 'rgba(0,0,0,0)' to set any background property to fully transparent.
• plot_bgcolor controls the inner plotting region.
• paper_bgcolor controls the entire figure background.
• For a truly transparent plot, set both plot_bgcolor and paper_bgcolor to transparent.
• You can apply transparency to other elements like legend backgrounds as well.