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How can I make the 'plot' function markers and lines transparent using 'alpha' or otherwise?

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I want to make a plot with semi-transparent markers and lines using 'plot' and 'alpha', but it's not working. Why?

Accepted Answer

MathWorks Support Team
MathWorks Support Team on 9 Jul 2021
Edited: MathWorks Support Team on 16 Sep 2021 at 14:18
Basic 'plot' function markers do not currently support transparency or alpha values. If you would like to make a scatter plot with transparent markers, it is suggested that you use the 'scatter' function and use either 'alpha' or set the value of the property 'MarkerFaceAlpha':
scatter1 = scatter(x,y,'MarkerFaceColor','r','MarkerEdgeColor','k');
% Set property MarkerFaceAlpha and MarkerEdgeAlpha to <1.0
scatter1.MarkerFaceAlpha = .2;
scatter1.MarkerEdgeAlpha = .2;
Or:
scatter1 = scatter(x,y,'MarkerFaceColor','r','MarkerEdgeColor','k');
alpha(scatter1,.2)
If you would like to have a line plot using 'plot' with transparent markers on top, you can simply use 'hold on/off' and 'scatter' in conjunction for the same desired effect:
plot(x,y);
hold on
scatter1 = scatter(x,y,'MarkerFaceColor','r','MarkerEdgeColor','k');
scatter1.MarkerFaceAlpha = .2;
hold off
Please see the "Input Arguments" list for the property 'value' on the documentation page for 'alpha' for a list of graphics objects that support face transparency:
  6 Comments
Théo
Théo on 18 Aug 2021
Same for me on 2021a: does not work anymore. It's crazy that in 2021, one of the biggest datascience software can not modify the opacity of its plot lines. We need a property similar to 'LineWidth' or 'Color', please!

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More Answers (3)

Rini Varghese
Rini Varghese on 4 Aug 2020
not sure if anyone is still following this, but for MATLAB's 'plot' function, color and transparency are specified as a 4 element vector, with the first 3 as rgb and last element as alpha value. For example, following will produce a red line with transparency 0.2.
plot(x,y,'Color'[1, 0, 0, 0.2])
  3 Comments
Rini Varghese
Rini Varghese on 8 Mar 2021
Right, yes, the 'plot' function won't allow you to change transparency for markers, just lines. One alterrnative is to use the 'scatter' function instead. You can individually specificy edge color, edge alpha, face color, face alpha... Hope this helps.
scatter(x,y,'o','MarkerEdgeAlpha',0.2)

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Zhongwei Yang
Zhongwei Yang on 12 Jul 2018
plot1.Color(4) = 0.2 works well. Amazing!
How could we know this keyword for the recent version, e.g., 2018a? How to use the manual or help to find it?

Peter Rochford
Peter Rochford on 28 Nov 2017
I have written a collection of Matlab functions for creating semi-transparent markers in plots and legends. The files are available from MATLAB Central as the MarkerTransparency package. A few examples of how to use these functions are included in the download and there is also a Wiki on GitHub. A major benefit of this package is it enables the user to have the semi-transparent markers also appear in the legend. This hopefully will meet your need.
  1 Comment
Maahi Shah
Maahi Shah on 9 May 2020
Hi Peter,
Thanks for sharing! Does the function setMarkerColor also work for 3D plots? I am trying to adjust opacity for my markers in a scatter3 plot.

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