Saving “heavy” figure to PDF in MATLAB - rendering problem

5
votes

I generate a figure in MATLAB with large amount of elements (100000+) and want to save it into a PDF file. With zbuffer or painters renderer I've got very large and slowly opened file (over 4 Mb) - all points are in vector format. Using OpenGL renderer rasterize the figure in PDF, ok for the plot, but not good for text labels. The file size is about 150 Kb.

Try this simplified code, for example:

x=linspace(1,10,100000);
y=sin(x)+randn(size(x));
plot(x,y,'.')
set(gcf,'Renderer','zbuffer')
print -dpdf -r300 testpdf_zb
set(gcf,'Renderer','painters')
print -dpdf -r300 testpdf_pa
set(gcf,'Renderer','opengl')
print -dpdf -r300 testpdf_op

The actual figure is much more complex with several axes and different types of plots.

Is there a way to rasterize the figure, but keep text labels as vectors?

Another problem with OpenGL is that is does not work in terminal mode (-nosplash -nodesktop -nodisplay) under Mac OSX. Looks like OpenGL is not supported. I have to use terminal mode for automation. The MATLAB version I run is 2007b. Mac OSX server 10.4.

3
pdfmatlabrenderingsave
actually for me zbuffer renderer produced a rasterized file similar in size to opengl one - Amro
Yes, it was the same speed for me, but I think that with an even more complicated graph where points aren't hidden so much by other points that opengl would be faster. - Justin Peel
As far as the opengl not working in terminal mode, what does typing opengl info tell you when in terminal mode in Matlab? - Justin Peel
>> opengl info Warning: OpenGL failed to load. - yuk
> zbuffer renderer produced a rasterized file similar in size to opengl. It happened with me as well when I was not in true terminal mode (without -nodisplay). Figure window appears on the desktop. - yuk

3 Answers

2
votes

This is a funny one. Your problem is not Matlab, it's Ghostscript (Matlab creates PDFs by calling Ghostscript, at least on Windows). When I run

x=linspace(1,10,100000);
y=sin(x)+randn(size(x));
plot(x,y,'.')
print -dpsc2 test.ps

I've got a 2Mb PS file (all vector, of course), which when compressed became a 164Kb ZIP. One would expect to get more-or-less the same result when converting PS to PDF, but ps2pdf test.ps produced your 4Mb file!

Since you are on a Mac, you probably have Distiller. I'd give it a try — generate PS files as above, and then run them through Distiller; you should get a 150K vector PDF.

If you insist on rasterizing, I can suggest printing the figure without any axes or labels to a tiff, opening the tiff, and recreating axes and labels on top of it.

1
votes

If you don't want to go with a 2D histogram (i.e. an image where pixel brightness corresponds to density of points) as BlessedKey suggests, it looks like the only good way is to do the rasterizing yourself, as mentioned by AB.

getframe followed by frame2im seems to be the way to go for that. Unfortunately, getframe returns empty if you run with -nodisplay. Therefore, you'd have to save the figure as .fig, and on another computer run a script that opens the figure, gets the content of the axes with getframe, displays the image from getframe and then saves to pdf.

As an alternative to simple plotting or a 2D histogram, you may want to look into scattercloud, which combines plotting the points with density information, by the way.

0
votes

If at all possible you should try to subsample your problem before building the illustration. If you are plotting points on a curve then 10,000 is probably more than you need. A modern printer is only about 600 DPI afterall.

If the points are illustrating a cloud with some density properties, a better solution may be to build a two dimensional histogram first, and illustrate that with imshow or imagesc.

If multiple clouds are being illustrated with different colors you may be interested in building one such image for each cloud and the combining them with transparency.