Converting .eps to .png Easily

ScottS-M — Wed, 14 Jan 2009 00:11:35 +0000

I end up generating a lot of postscript plots in R and other programs. Unfortunately, a lot of not so technical people have trouble opening postscript files so I end up having to convert these images to other formats pretty often. A really handy program for converting eps files to png (or jpg although that's not really an optimal format for plots) is ImageMagick (available for all OSs I believe). ImageMagick lets you quickly convert (and create thumbnails, make B&W,...) from the command line without having to open up Photoshop.

For example, to convert an image named myPlot.eps to png you just need to enter convert myPlot.eps myPlot.png (convert is a program in the ImageMagick package) at the command prompt and you'll get a png file in myPlot.png. If you want to adjust the resolution (the default resolution is 72 dpi) of the output image, you can add the -density option (e.g. for 200 dpi convert -density 200 myPlot.eps myPlot.png). Make sure you put the -density part before the input image name.

Converting many files at once is where ImageMagick really shines. The mogrify command is probably the quickest option. For example, to convert the files image01.eps, image02.eps and image03.eps to png, just use the command mogrify -format png image*.eps. In one shot, it will create image01.png, image02.png and image03.png.

Unfortunately, recent version of Imagemagick seem to be treating eps to png conversions oddly (see below) so mogrify isn't cutting it on my files. If you have similar trouble (and you're on Unix or Mac or Cygwin), you can just use a bit of Bash combined with the convert command to get around the problem like this:

BASH:

for f in `ls *.eps`; do
convert -density 100 $f -flatten ${f%.*}.png;
done

Black Background Problem

As I mentioned above, I started having trouble converting from eps to png after upgrading to ImageMagick 6.4. The transparent/white backgrounds in my eps files were being converted to black backgrounds and making the figures unreadable. I guess it must be some change in how transparency is handled but I'm not totally sure what changed. It took me a bit of googling before I found the solution, so I'll repost it here. Adding -flatten to the command (e.g. convert myImage.eps -flatten myImage.png) should change the background back to white. My mogrify command doesn't include the -flatten option so convert (like the example above) seems like the way to go.

SAS lag problems

ScottS-M — Wed, 27 Sep 2006 23:07:23 +0000

I just found an interesting (that's interesting in the 'I just spent an hour debugging that?' sense) characteristic in SAS. If you have a variable, x, and are using the lag of x, do NOT put the lag(x) inside a conditional statement. This can apparently cause some pretty strange results. It is probably easier to see through code than to explain:

SAS:

data test;
input id$1 x;
cards;
a 1
a 2
a 3
b 12
b 13
b 15
run;
data test;
set test;
lagid=lag(id);
if lagid=id then do;
lagx=lag(x);
duration=x-lagx;
end;
run;
proc print;
run;

And here are the results:

SAS:

Obs id x lagid lagx duration
1 a 1 . .
2 a 2 a . .
3 a 3 a 2 1
4 b 12 a . .
5 b 13 b 3 10
6 b 15 b 13 2

There are obviously some strange things going on here. I have no idea what is going on in the 2nd row of the results where lagx is missing when it should be 1. And in the 5th row, lagx is the 3 from 2 rows above when it should be 12. Luckily, the solution is easy. Just execute the lag every time:

SAS:

data test;
set test;
lagid=lag(id);
lagx=lag(x);
if lagid=id then do;
duration=x-lagx;
end;
run;

Anyway, it took me two years to run into this so I guess this isn't a common mistake but if you're ever having trouble with a lag, check to make sure it is executed for every line of the data.

Dammit Jim! » problem

Converting .eps to .png Easily

Black Background Problem

SAS lag problems