How do I extract data from MATLAB figures?

I have a few MATLAB figures, but no MATLAB code associated with it. I want to extract the data from the curves in the figures.

Answer 1

[MathWorks Support Team]

This example shows how to extract data from a MATLAB figure.

If the figure is stored in a file, such as 'example.fig', then open the figure file using 'openfig'. Assign the Figure object to the variable 'fig'.

fig = openfig('example.fig');

If the figure is already open, then use 'gcf' to access the Figure object and assign it to the variable 'fig'.

fig = gcf;

There are several ways to access the data for the plotted graphics objects. You can use the Children property or you can use 'findobj'.

Use Children Property

Access the plotted graphics objects through the Children properties. The Axes objects are children of the figure. The plotted graphics objects are typically children of the Axes object.

axObjs = fig.Children
dataObjs = axObjs.Children

The 'dataObjs' array that appears in the Command Window indicates the types of graphics objects in the axes. Different graphics objects store data differently. For example, Line objects store the data in the 'XData', 'YData', and 'ZData' properties. If the first element in 'dataObjs' is a Line object, then access its data using this code.

x = dataObjs(1).XData
y = dataObjs(1).YData
z = dataObjs(1).ZData

If the figure contains other types of graphics objects, then use the appropriate properties to access the data. For a list of graphics objects and their properties, see:

https://www.mathworks.com/help/matlab/graphics-object-properties.html

Use findobj Function

Alternatively, you can find all the graphics objects in a figure with a certain data property. For example, find all graphics objects that have a 'YData' property. Then access the 'YData' values for the first object.

dataObjs = findobj(fig,'-property','YData')
y1 = dataObjs(1).YData

[Carlos]

I successfully used this code to extract data from a .fig file before.

I attempted to extract data from another .fig file and I was unable to. I received this error message:

Error using get Invalid property found. Object Name: text Property Name: 'XData'.

Error in extract (line 23) xdata = get(dataObjs, 'XData'); %data from low-level grahics objects

I am new to MATLAB and I am unsure how to get this to work.

[Walter Roberson]

lineObjs = findobj(dataObjs, 'type', 'line');
xdata = get(lineObjs, 'XData');

[dhhtr]

Neat trick!

[Marianna Biscarini]

Hi, thanks for the very useful suggestions.

I have some problem when the file .fig that I open contains more figures and each figure is composed by several subplots.

How do I extract data from one precise subplot of one precise figure contained in the .fig file?

[Michael Judge]

Hello all,

Just wanted to point out that, if the data were plotted as a 2D matrix (where each row is a different line), none of the solutions on this thread give back the initial matrix (after conversion of YData to a matrix, of course). In fact, the rows in the extracted data are all out of order.

Any thoughts on this? Are lines created/indexed in any particular order when they are plotted from a matrix?

Thanks, Michael

[Walter Roberson]

When you plot a matrix by columns, then the order of handles returned from the plot() call is the order of the columns:

data = sort(rand(20,5),2);
h = plot(data);

Now h(1) corresponds to column 1, h(2) corresponds to column 2, and so on. You can confirm this with:

h(1).DisplayName = 'col1';
h(2).DisplayName = 'col2';
h(3).DisplayName = 'col3';
h(4).DisplayName = 'col4';
h(5).DisplayName = 'col5';
legend();

and see that indeed the item labeled col5 is the one with highest average Y (it was constructed that way by the sort() call).

However, the order of axes children defaults to the reverse of this:

>> get(gca,'Children')
ans = 
  5×1 Line array:

    Line    (col5)
    Line    (col4)
    Line    (col3)
    Line    (col2)
    Line    (col1)

because the rule is that the axes children are (by default) painted from last to first (first is on top, last is on bottom). This can be altered in a few ways, including some obscure specialized settings that were new in R2014b, but also the order can be changed with good old uistack()

When you recall a figure file and pull out the axes children, the axes children are going to be in the same order as was present in the axes when it was saved to the figure file. If nothing in the original code altered the order, that is going to be last column first. So if you retrieve the YData and mat2cell() it into a 2D matrix, make sure to fliplr() to get the original order.

[Daniel Enderich]

Hi all,

Regarding subplots, I found that simply entering in "subplot(n,m,p)" to direct MATLAB to your desired subplot does the trick. Add it before you set a=get(gca,'Children'); There's probably a more clever way of doing it, but it worked for me. I'm using Felipe Bittencourt de Souza's solution below and 2018b.

Answer 2

[Felipe Bittencourt de Souza]

I was having the same error message mentioned before: "Error using get Conversion to double from cell is not possible."

I solved this issue with Walter Roberson's answer, using the following code:

open('example.fig');

a = get(gca,'Children');

xdata = get(a, 'XData');
ydata = get(a, 'YData');
zdata = get(a, 'ZData');

Answer 3

[Yair Altman]

Note that the official MathWorks answer above relies on opening and displaying the figure (using the open() function) before extracting its contents. This is both slow and potentially unwanted (we don't always want to display the figures), especially if we're looping over many FIG files.

Instead, users can directly read and analyze the *.fig file by loading it into Matlab memory using the load() function, since *.fig files are basically simple MAT files with a .fig (rather than .mat) file extension.

Fortunately, the internal format of these files has changed very little over the years - a few fields have changed their name, but the basic file data structure remained the same. So essentially the same code can be used to extract data from .fig files created a decade ago, as well as the latest Matlab release.

Note that the fact that FIG files are basically just MAT files is an undocumented feature of Matlab, and so it might change one day. But for now it is a very handy feature to use.

Additional information: https://undocumentedmatlab.com/blog/fig-files-format

Answer 4

[Michael]

I tried to follow these steps, but when I got to objTypes = get(dataObjs, 'Type') I got this error:

Error using get Conversion to double from cell is not possible.

I don't know Matlab's figure format and I'm not familiar with Matlab's API for accessing figure data. I'm not sure what this error means.

If anyone else happens upon this: Matlab figures are just ".mat" files. The scipy.io library in Pylab can read Matfiles into numpy structures using the 'loadmat' command. One can then browse the figure data in Python and locate the data.

Edit: one can also step through the figure data in Matlab, by loading the figure using the command "s=load('Figure.fig','-mat')". The solutions using "get" never really worked for me. I think this is because every figure is structured slightly differently, and people are posting solutions that work for a particular figure, but don't generalize well. If you just grab the figure data structure, you can step through it and find what you need.

[Cameron]

I managed to get a similar error when running the line:

dataObjs = get(axesObjs, 'Children');

I'm not entirely sure why it's unable to access the handles using the 'get' method, but changing the code to

dataObjs = axesObjs.Children;

seems to have done the trick. Hope this helps.

[Julia Mödl]

i tried all answers and always get an error. i got the converting to double error too and with the last answer i got this error: No appropriate method, property, or field 'Children' for class 'matlab.graphics.Graphics'.

Error in daten_auslesen (line 5) dataObjs = axesObjs.Children; I dont know how to fix this code, so id be happy to get some help.

[Walter Roberson]

Julia Mödl : you would have that problem if the axes you were looking at was a placeholder rather than an axes object.

all_axesObjs = findobj(h, 'type', 'axes');

now only examine the items in all_axesObjs.

Or use what I posted earlier,

lineObjs = findobj(dataObjs, 'type', 'line');
xdata = get(lineObjs, 'XData');
ydata = get(lineObjs, 'YData');

Answer 5

[Parrish.Ch]

Hi all,

I noticed people were having issues with getting the following error when attempting to run:

objsTypes = get(dataObjs,'Types')
Error using get Conversion to double from cell is not possible.

I think I have a solution to the issue. For surface plots, I noticed that the children of an axes object (so dataObjs in this case) may contain a subgroup that is a complex cell. You have to use cell2struct to break this cell into it's basic pieces so you can extract the data. Here is the code for my solution:

h = gcf;
axes = get(h,'Children');
dataObjs = get(axes,'Children');
Props = cell2struct(dataObjs,'SurfaceProps',2);
SurfaceData = Props.SurfaceProp;
XData = SurfaceData(3,1).XData;
YData = SurfaceData(3,1).YData;
ZData = SurfaceData(2,1).ZData;

**Before you just copy paste this code, there are a few important things to know.

My variable dataObjs is a 2x1 cell. The first index in the cell is empty but the second index is a 3x1 Group. I have to convert this cell group to a structure that can then be used to access my data. From there, I use cell2struct on the second index to accomplish this. The cell2struct generates a property that is named in the second argument of the cell2struct command ('SurfaceProp' for me). Props.SurfaceProp extracts the various "children" from the 3x1 Group in dataObjs. In my case, I have three objects in Props.SurfaceProp: two light objects and one surface object. The surface object contains the x, y, and z data. My surface object is the third index in the matrix generated by Props.SurfaceProp, so I use SurfaceData(3,1).XData to access the XData handle that is in the third index of the SurfaceData array.

I hope this helps!

[Houghton]

I tried your code. But I got an error.

Undefined function 'cell2struct' for input arguments of type 'matlab.graphics.primitive.world.Group'.

- I typed

which cell2struct

- I got the answer

built-in (/Applications/MATLAB_R2014b.app/toolbox/matlab/datatypes/@cell/cell2struct) % cell method >>

what should I do?

Thanks

[Walter Roberson]

Would you have some simple code that recreates this problem? My simple test does not create that kind of group, but it could well be that a different call does.

Answer 6

[Daniel Ares]

Hi to everybody,

i can´t run it, i get this error, with this code.

open('Force vs Time.fig');
h = gcf; %current figure handle
axesObjs = get(h, 'Children'); %axes handles
dataObjs = get(axesObjs, 'Children'); %handles to low-level graphics objects in axes
lineObjs = get(dataObjs, 'type', 'line'); %type of low-level graphics object
xdata = get(lineObjs, 'XData'); %data from low-level grahics objects
ydata = get(dataObjs, 'YData');
zdata = get(dataObjs, 'ZData');

Thanks

[Jan]

You forgot to mention the error you get. But please remove this message and post it as a new question, because this is the section for answers. Thanks.

You will get an answer like:

lineObjs = get(dataObjs, 'type', 'line')

get() does not accept 3 inputs. Do you mean:

lineObjs = findobj(dataObjs, 'type', 'line')

? Note: Please delete this message even if this solves your problem.

Answer 7

[Chetanya]

I wrote a small function to extract data from file following the MATHWORKS staff answer. Here it goes, https://www.mathworks.com/matlabcentral/fileexchange/73274-extract_data_from_figures?s_tid=prof_contriblnk

Please feel free to suggest if you find any bugs.

Answer 8

[Yun-Han Lee]

A simple workaround with a bit sacrifice in precision (pretty manual though):

1. Open a figure, and then Tools>Basic Fitting.

2. Choose 'shape perserving interpolant,' then hit the arrow at the buttom twice to expand to the full panel.

3. Enter x of interest, then Evaluate, and then Save to workspace.

Answer 9

[Abhishek Shahi]

I hope this will help

x = get (gco, 'XData');
y = get(gco, 'YData');
z = get(gco, 'CData') ;

[Walter Roberson]

unfortunately you need more complicated. gco is only the currently active object, which is the last object brought into focus deliberately or by clicking on it. The form you used will not look for children objects, so if the figure is the current object it would not track down to a plot object to extract the information. The code will also fail if the current object does not happen to have Xdata such as if an axes is the current object.

If you had just loadfig() then it would be most common that the current object would be the last axes in the figure, but there is a lot of variability in that.