2Â¥: Originally posted by FMStation at 2016-08-29 20:25:30
http://muchong.com/bbs/viewthread.php?tid=10071457&fpage=1&target=blank
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1) reduce the graphics of the plot to the plain plot area (i.e. the axis-bound area)

2) import into matlab and display:

imdata=flipdim(imread('fig1.png'),1);

implot=imref2d(size(imdata));
implot.XWorldLimits=[xmin xmax];
implot.YWorldLimits=[ymin ymax];
imshow(imdata, implot);

% if y is logarithmic (for x accordingly...)
set(gca,'YScale','log');
% you might have to flip the axis direction
set(gca,'YDir','normal');
% you probably want to adjust the image aspect ratio.
set(gca,'DataAspectRatio',[1 70 1]);

note: xmin, xmax, ymin, and ymax are the limits of the axes. replace them manually with the values of your figure.
now you have a matlab reproduction of the figure, you like to have the data from.

3) "grab" the coordinates of a number of data points (npoints):

[x,y] = ginput(npoints)

move the mouse to the respective data points and (left) click. when clicked npoints, x and y coordinates of the npoints points in the plot's system are now stored in vectors x and y, respectively.