Matlab figures in Powerpoint

I've just been putting together a presentation in which I wanted to include a set of Matlab plots. Whilst there are plenty of ways to do this I thought I would detail the way I managed it...

I've mentioned before about maintaining quality by using vector graphics. Previously I've used .eps format for this, but I don't think it's well supported in Powerpoint (I did consider using alternative presentation software but I was pressed for time and this seemed like the easiest option). Instead I used .emf format which seems pretty well supported by Matlab. This is a Windows specific format so I can't say I'm particularly keen on it for general use, but it served a purpose here.

I saved my figures as separate images from Matlab and then imported into Powerpoint, but I think the same result can be achieved if you simply copy and paste between the two.

One of the benefits of having the plots in vector format is the ability to manipulate them within Powerpoint itself. For the unscrupulous this could be a good technique for "adjusting" a few points here and there to improve  your results - but obviously I didn't do that! What I did do was separate out several lines that were on the same plot, so that I could make them appear (using Powerpoint's animation features) gradually. This made the plots (which were a comparison of the results of several different simulations) much cleaner.

It was a little bit of a hassle to do this, but not awful, and I think worthwhile as it made the results much easier to present. When the .emf file is initially imported it is handled as an image; however, if you right click on it you will find that it can be "ungrouped". You might have to repeat this process a few times as the image seems to be built up of several sub-groups, but once you're done you'll find that individual lines are available to be manipulated. Unfortunately I then had to go through and "regroup" some of them manually to reform complete lines, which involved a bit of 'Ctrl' clicking - this was the tedious bit. I guess it depends how complicated the lines in your plots are as to how long this will take (and whether it is worthwhile or not).

Another benefit was being able to alter the font of my axes to match my presentation style. A trivial point perhaps, but it all goes to improve the overall appearance.

So to summarise:

1. Copy figure in Matlab
2. Paste in Powerpoint
3. Right click and "ungroup"
4. Repeat 3. until you get to a  level that you can manipulate the objects that you want
5. You may find there are a few large white squares that form the background of the plot - these can be deleted (it will make things easier when you come to regrouping things in step 7.)
6. 'ctrl'+'a' to select everything and then change the font to match your presentation
7. 'ctrl' and click on objects to collect all the ones that should be in a group (you may need to zoom in on your slides to do this accurately)
8. right click and "group" them
9. move/recolour/animate/resize the objects as you desire to suit your presentation!

Hope that is of help to someone!?

Simulink to eps

I've mentioned previously that I've developed a process to export plots from Matlab and include them as (eps format) figures in a Latex document. Well today I spent a load of time trying to get a similar method working for exporting Simulink model diagrams from Matlab. This hasn't proved quite as easy, but I think I'm there now.

My main issue was that Simulink doesn't allow you to print in the same way as a normal Matlab figure does. The "print" command can be used, but it works in a very specific way. It is fairly easy to use this command to print in eps format (see my previous posting for why this is a good thing); however it doesn't allow you the same freedom to setup the page. More specifically it will only allow you to use a pre-defined page size (A4, US legal, etc). It rescales and centres the figure to fill the page, but, unless the model is the exact same aspect ratio as a pre-set paper type, you end up with white borders at either the top/bottom or left/right.

EDIT: This seems to have been corrected in newer versions of Matlab now!

I've tried all sorts to get round this, including calling Ghostscript from within matlab to post-process the eps file. This should work as it ought to be able to find the right "bounding-box" for the figure and resize the page accordingly. However I had no luck with this - it would either not trim it down at all, or over-trim it removing some of the image.

I also tried exporting in a few other formats (namely normal postscript and pdf) and then converting with Ghostscript. This worked a little better and I was able to get the right bounding box through a process of:

1. Simulink export to pdf, 
2. Ghostscript convert pdf-to-eps, 
3. Ghostscript convert eps-to-eps. 

I have no idea why that last step was necessary! Unfortunately although the output from this was pretty good, the text becomes part of the image (I think during the second step), meaning it doesn't render properly at high zoom levels. I don't know why that happened, I'm pretty sure it shouldn't have, but I thought I could do better.

So an alternative process I finally came up with is:

1. Find out the ratio of the figure (I did this by exporting as a raster image and then reading back in - I'm not very happy with this technique as it's pretty dirty, but at least it works)
2. Simulink export to eps, with the model at the very bottom of the page
3. Automatically edit the resulting eps file to adjust its bounding box information

It's a bit hacky, and if I was being picky the margins aren't perfectly even in the resulting file, but it seems to work. I'm sure there must also be a better way of achieving step 1, but it's sufficient for now. (If anyone has any suggestions then I'd love to hear them!?)

There's nothing very clever in the code, but if anyone wants a copy of my function I'll happily forward it to them. Hope this helps somebody!

EDIT: Code for my function is available here.

Professional plotting

I've written and read plenty of technical reports in my time, and one major feature that almost all technical reports have in common is the inclusion of figures. Pick up any ten technical documents and I reckon you'll find at least 5 different ways of including figures; and of these 5 only one will actually look any good. So as I start to produce figures for my PhD I've been starting to look into the best way of managing this initially simple sounding task.

When I say "figure" I'm generally thinking of some kind of plot, or set of plots, usually in 2D; however what I'm going to discuss should apply to most other "technical" "pictures", but probably won't extend to photo-type images (for reasons that will hopefully become obvious).

The Issues
I won't bother going into all the different ways a figure and a report might come together, except to say that at the very bottom of the scale would be a 'picture'/screenshot pasted into a word document - this just looks awful. What I'll work up to will hopefully be the top of the scale.

What I will list is what I see as some major stumbling blocks in figure/report preparation:

1. Difficulty updating the figure.
2. Inability to resize the figure to suit the report.
3. Images (+ text) looking crappy when zoomed in.
4. Disconnect between the figure labels and the report text.
5. Difficulty regenerating the figure at a later date.

A lot of these are irrelevant when we're looking at a printed out finished article, so what we really need to understand are the details of how the information is stored and processed on the computer.

Background Details
One of the first important distinctions is the difference between types of image. Most images that one would typically come across on a computer are raster images, these are stored as a set of pixels - imagine a piece of squared paper with each square filled in a different colour. From a distance, or if all the squares are very small, then this looks great; however if we zoom in (e.g. make each square larger) then we start to see the joins between edges and everything starts looking "blocky". Most programs usually handle this by blurring the pixels together slightly, which can help up to a point, but often we just end up with a blurred mess - not what we want in a precise technical report.

The alternative is vector graphics. These are saved more as a description of what needs to be drawn, rather than point-for-point what is on the screen. This means that zooming is purely a mathematical operation, and all the lines will still appear as prefect lines. The same also works for text, which is stored within a vector graphic as actual text, rather than as a picture of it.

There are plenty of graphics explaining this along with a good description in the Wiki pages linked above. But if you're still not sure then try this simple experiment: type a word into a paint program (e.g. Microsoft Paint) and zoom in, and then do the same in a word processing program (e.g. Microsoft Word) - the difference should be pretty obvious.

In summary, unless what your are working with is an actual picture (in which case converting it to vector graphics would be impossible) then you will get best quality out of maintaining it in a vector format. There are plenty of these formats to choose from; however I find them to be surprisingly unsupported in a lot of applications. As my final target format is pdf (as mentioned elsewhere in this blog) I'm going to be working with eps and pdf formats. These both rely on postscript as an underlying process and are therefore fairly compatible.

My process (overview)
With all of the above as my aims I've worked out a basic process for generating figures. It seems to be working fairly well so far, so I'll outline it here:

1) Write a script to produce the figure and save is as an eps file. This means that I can always go back and see how each figure was produced (what the original data was, how it was scaled, etc, etc). If the data changes then I can simply rerun the script and a new figure will be produced. If I need the figure in a different ratio or with different colours (or a different label, etc, etc) then I can make some minor changes to the script and rerun it. I keep the script under version control, but not the eps file it produces (as I can always reproduce this if necessary). I use Matlab for this process as it is what I am most familiar with (although I often store the raw data in an excel or csv file and read this into Matlab). I suspect I could use Gnuplot or something similar instead.

2) Include the eps file in my LaTeX script. This means that when I regenerate the pdf output from my LaTeX it always includes the most recent version of the figure. As it remains as vector graphics throughout the process I get nice clean professional results.

This process solves all of the problems outlined above, except point 4. It is still possible to produce an eps figure from Matlab with "Courier" font and then include it in a Latex document using "Times" font. I find that this looks out of place. I get around this by using a function called matlabfrag, in combination with pstool package for LaTeX. This means that the final figure picks up the font used in the rest of the document. It also allows me to use full LaTeX expressions in my figures.

My process (in detail)
This may get more refined as time goes by, but currently this is the detailed version of how I would produce a figure:
1a) Write a Matlab script to plot the figure as normal. Using standard matlab command to plot and label axes, etc.
1b) Within the script include a call to 'saveFigure.m'. This is a function I have created which accepts a file name and optionally a figure size (otherwise some default values are used), resizes the figure and then calls matlabfrag to save it as an eps file (and an associated tex file including all the labels).
2a) In the LaTeX preamble include '\usepackage{pstool}'. This allows the use of the psfragfig command.
2b) Within my LaTeX include the figure in the normal way. However, instead of using the latex '\includegraphics' command, I replace it with the '\psfragfig' command.

Notes
I can make my 'saveFigure.m' function available to anyone interested, but it doesn't do much more than I have described above!
I have created a slightly revised process for including Simulink models in documents which is a little different that I can discuss if anyone is interested?
I spent a little time trying to get psfrag to play well with eps files produced from other packages - e.g. Google Sketchup, however I don't think I've quite got to the bottom of it yet.