#!/usr/bin/perl
=head1 NAME

process_ppm_pipeline - process a pipeline of multiple PPM images

=head1 SYNOPSIS

 process_ppm_pipeline  magick_args....

 Extra non-Imagemagick options:
    -help
    -manual

=head1 DESCRIPTION

Read from standard input a pipline of PPM images (pnmnoraw) and run the
specified imagemagick magick arguments on them. The resulting image is
then feed to the output as pipeline of normal PPM images.

For example, process a very long video sequence...

 ffmpeg input.mpg -f image2pipe -vcodec ppm | pnmnoraw |
   process_ppm_pipeline -flip |
 ffmpeg -f image2pipe -vcodec jpeg output.mpg

OR for GIF animations...

 magick animation.gif  -coalesce  -compress none ppm:- |
   process_ppm_pipeline  logo.gif -gravity SouthEast -composite   |
 magick -   -layers Optimize -set delay 10 -loop 0 animation_new.gif

The magick arguments should assume only one image has already been
read into memory and should not provide a final output filename.

=head1 WHY

The reason this script is needed is that while "magick" and other
ImageMagick commands can read a pipeline of PNM images, it will read ALL
of the images into memory.  This is not good if you are processing
a video stream, as you would end up with the whole (huge) video,
uncompressed, fulling memory.

This program splits up the ASCII-PPM images and processes each image
as it is seen. At no time is more than one image being handled.

This program was created after a discussion on the IM Users Forum
http://www.imagemagick.org/discourse-server/viewtopic.php?f=2&t=18320&p=71150

=head1 FUTURE

This script could be made better, by feeding the image directly into the
magick command while it is still looking for the end of image to be
found.  That is without buffering the whole (single) image itself!

Also with a little more savvy it could know exactly how many bytes needs
to be read and passed on to the "magick" comamnd, using a binary (raw)
PPM file format, without over-reading into the next image.

In the same way, it could also be made handle a ImageMagick MIFF image
format, allowing the complete image meta-data to be preserved with each
individual image, and not just the basic image data.

=head1 AUTHOR

  Anthony Thyssen  8 April 2011  A.Thyssen_AT_griffith.edu.au

=cut
# -----------------------------------------------------------------
use strict;
use FindBin;
my $PROGNAME = $FindBin::Script;

# Perl Pod Usage Method
sub Usage {
  eval {
    use Pod::Usage;
    pod2usage ( @_ );
  };
}

# provide help
Usage("$PROGNAME: No Arguments Found") unless @ARGV;
Usage(-verbose => 1) if grep( /-+(\?|help)/, @ARGV);
Usage(-verbose => 2) if grep( /-+manual/, @ARGV);

# -----------------------------------------------------------------
my $image;

sub run_magick {
   open(CVT, "|-")
       or exec( 'magick', '-', @ARGV, 'ppm:-');
   print CVT $image;
   undef $image;
   close CVT;
   exit $? if $?;
}

$image = <STDIN>;

Usage "Input is not ASCII-PPM images! Did you forget to use 'pnmnoraw'?"
     unless $image =~ /^P3\s/;

while ( <STDIN> ) {
  run_magick   if /^P/ && $image;
  $image .= $_;
}
run_magick if $image;

exit 0;
# -----------------------------------------------------------------