nullprogram.com/blog/2007/12/26/
Update May 2015: Somehow the original script was lost while changing
hosts four years ago. I’ve replaced the script with a smaller,
better, standalone C program. Note: it has a different interface, so
read the header first!
I had written a previous post called Movie DNA where I
described a simple way of distilling an entire movie down to a single
frame. It involved the use of two tools, with no intermediate code or
software in the middle to glue things together.
The first tool, mplayer was used to dump all of the frames we needed.
This took about the running length of the movie to do, which wasn’t so
bad. There may be a way to speed this up by giving mplayer some extra
hints. I have not yet figured this part out.
The real time cost was in ImageMagick’s montage tool, which made the
final montage out of the images. This took between 6 and 10 hours to
do this, depending on the length of the movie. The process seemed to
be non-linear for some reason, with long movies taking
unproportionally longer to process (One could always dig around the
montage source to find out why). I knew there had to be a way that
this could be improved!
Well, I wrote a Perl script last night, dubbed gdmontage to speed up
the montage process. It was even faster than I thought it would be,
taking only 12 seconds on the same machine as before. It uses the
GD Graphics Library via Perl’s GD module, which you
would need to install to use this. It also uses the
Term::ProgressBar, if it’s available, to provide a progress
bar and ETA.
Like the original montage program, the script recognizes file globs,
so you can provide the files through a glob in order to avoid the
limits on command line arguments.
$ ./gdmontage.pl "frames/*"
It is a bit unfair to call my code a “faster montage” because it only
covers a tiny subset of the original montage. It makes some big
assumptions in order to be faster; specifically, it assumes that every
image is the same size. The original montage must look at every image
before it even starts in order to determine the dimensions and
placement of the final image.
It is also geared towards the Cinema Redux thing, doing only 60 images
per row. This can be changed internally (no command line arguments for
this) by adjusting the parameters at the top of the script. The script
could probably be easily expanded to include most of the features of
ImageMagick’s montage, but I am sure this Perl script would be much
faster when it comes to creating large montage’s. (Why is montage so
slow?)