How do you save a figure with a trasparent background?

How do you save a figure with a trasparent background? I want to save a figure as a png image that has a transparent background so I can put the image into PowerPoint and the PowerPoint graphic will show through the Matlab figure.

Answer 1

[jonas]

The most recent version of export_fig includes a -transparent option for .png export

[Ron Beck]

Thanks for the tip. It worked for outside the polar plot. I would like to have the inside the polar plot transparent also if possible. Is it simply another setting? I just want the plotted lines to show up.

[jonas]

set(gca,'color','none')

or in case it doesn't work you can set it to default,

set(0,'DefaultAxesColor','none')

[Ron Beck]

Thanks for the response, but neither worked. Is it critical where I put the lines of code?

[jonas]

Sorry for the late response. If you did not solve it already perhaps you can upload the code and I will have a look.

The first option calls the current axis (gca), so it should be located after the figure. The other option should be at the beginning of the code.

[DGM]

So that we have an example:

% a figure with a line plot
x = linspace(0,2*pi,100);
y = [sin(x); cos(x)];
plot(x,y)
xlim([0 2*pi])

% write a transparent PNG using FEX export_fig()
fname = 'output.png';
export_fig(fname,'-transparent',gcf)
% since it's a PNG with transparency, 
% you must retrieve the alpha channel separately.
% most native tools (e.g. imshow) will not directly handle an RGBA image.
% for info on handling RGBA images within MATLAB, do a forum search
[inpict,~,alpha] = imread(fname);

Note that this inserted image is transparent both within and outside the plot box. It just doesn't show since the page background is also white.

Answer 2

[cui,xingxing]

since Matlab R2020a, use "exportgraphics", for example ,you can do like this

x = 0:.1:2*pi;
y = sin(x);


% save to transparented image
figure;
plot(x,y,'LineWidth',4);
set(gcf, 'color', 'none');    
set(gca, 'color', 'none');
exportgraphics(gcf,'transparent.eps',...   % since R2020a
    'ContentType','vector',...
    'BackgroundColor','none')

[Niklas Kurz]

Awesome, thank you for providing this information!

[James Van Zandt]

is it no longer supported?

pdf

Warning: Background transparency is not supported; using white instead.

png

Warning: Background transparency is not supported; using white instead.

eps

Warning: Background transparency is not supported; using white instead.

>> ver

-----------------------------------------------------------------------------------------------------

MATLAB Version: 9.9.0.1467703 (R2020b)

[James Van Zandt]

Pardon - I was commenting on a previous suggestion. Here's the relevant code:

fprintf('pdf\n'); exportgraphics(gca,'l16.pdf','BackgroundColor','none');

fprintf('png\n'); exportgraphics(gca,'l16.png','BackgroundColor','none');

fprintf('eps\n'); exportgraphics(gca,'l16.eps','BackgroundColor','none');

[Darcy Cordell]

Does this also work for png format? Doesn't seem to work for me...

[haoming]

Hi, I received the same error

my code is:

exportgraphics(gcf,'sweep_plot.jpg','Resolution',600,'BackgroundColor','none')

error:

Warning: Background transparency is not supported; using white instead.

[Juan]

Haoming,

you are trying to generate a jpg with a transparent background, which is not supported, change it to png and it should work

[Aditi]

Tried changing the figure type to png. It still shows the same error

Answer 3

[Subba Reddy]

Non matlab way, Can use gimp software to remove white background from image, by selecting the background with color select tool, invert selection and copy. Then create new gimp window with background option as tranperancy, and paste it into that and export that as png. Not programmable but can be used to prepare images for presentation.

[DGM]

Even within GIMP, that's not a great way to approach the problem. While GIMP does provide antialiased selection tools, we don't have to deal with the fringing that they'll still cause.

Aside from color-based selections, MIMT does have an equivalent to GIMP's Color to Alpha plugin:

% a figure with a line plot
x = linspace(0,2*pi,100);
y = [sin(x); cos(x)];
plot(x,y)
xlim([0 2*pi])

% take a screenshot of the figure
outpict = frame2im(getframe(gcf)); % RGB, uint8

% let's be lazy and just use MIMT color2alpha().
% this is the same as the GIMP plugin of the same name.
opc2a = color2alpha(outpict,255/255); % RGBA, uint8
% the color parameter is unit-scale and automatically expanded.
% since the interior and exterior of the plot box are 255 and 240 (in modern versions)
% the plot box is now 100% transparent, 
% while the exterior area is slightly opaque.

% IPT imshow() doesn't handle RGBA images, but MIMT imshow2() does
imshow2(opc2a)

% most native tools don't handle RGBA images 
% so it may help to split the color from the alpha
[colorout alphaout] = splitalpha(opc2a);
imwrite(colorout,'output2.png','alpha',alphaout)

Again, the transparency in this image doesn't show up due to the white page background.

Otherwise, we can use other color-based selection techniques to do this programmatically in MATLAB without needing to use GIMP. There are lots of examples here on the forum.

Answer 4

[W. Jeremy Morrison]

This is my method to programatically generate transparent-background PNG files from Matlab figures. I use a Mac, but this should be the same process on windows.

Note: This method requires the inkscape command line tool. Installing this should be fairly easy.

(1) Generate the desired figure in Matlab and save it as an .eps vector graphic.

f = figure(fNum);
exportgraphics(f,[savePath '/' name '.eps'],...
    BackgroundColor="none",ContentType="vector");

(2) Use inkscape command line tool to convert from .eps to .png and remove the .eps file. Use system() to work on the command line while in Matlab.

system([inkscapePath ' -d 600 ' savePath '/' name '.eps'...
        ' -o ' savepath '/' name '.png; rm ' savePath '/' name '.eps' ]);

Here inkscapePath pints to where the inkscape tool is installed. You can find this path by typing 'which inkscape' into your terminal. The -d flag of the inkscape tool conotrols the dots-per-inch, i.e. the resolution, of the converted .png file. The default is 96, which is pretty horrible.

Example on my Macbook:

% example that plots the standard normal distribution and converts it to
% a .png with transparent background
% kept the formatting the same as above for better understanding

% discretise and compute pdf values
xvec = linspace(-5,5,100);
pdfvec = normpdf(xvec);

% plot
f = figure(1); clf(1);
plot(xvec,pdfvec);

% set the x and y axes to invisible
f.CurrentAxes.Visible = 'off';

% export as .eps file to the current working directory
savePath = '.';
name = 'normpdf';
exportgraphics(f,[savePath '/' name '.eps'],...
    BackgroundColor="none",ContentType="vector");

% use inkscape to convert to .png file
inkscapePath = '/opt/homebrew/bin/inkscape';
system([inkscapePath ' -d 600 ' savePath '/' name '.eps'...
        ' -o ' savepath '/' name '.png; rm ' savePath '/' name '.eps' ]);

Output: