#!/usr/bin/perl -w
# ppmtopgm.pl - Don Yang (uguu.org)
#
# Different versions of ppmtopgm produced slightly different outputs.
# To make PGM tests deterministic, we use our own version of ppmtopgm.
#
# 12/25/11

use strict;

my @lines = <>;

# Check header
if( $#lines < 3 ||
    $lines[0] !~ /^P3/ ||
    $lines[1] !~ /^\d+\s+\d+/ ||
    $lines[2] !~ /^255/ )
{
   die "Error parsing header\n";
}

# Copy header to output
print "P2\n", $lines[1], $lines[2];

# Convert pixels
for(my $i = 3; $i <= $#lines; $i++)
{
   while( $lines[$i] =~ s/^(\d+)\s+(\d+)\s+(\d+)(\s+)(.*)/$5/s )
   {
      my $p = int(($1 * 299 + $2 * 587 + $3 * 114) / 1000);
      if( $p > 255 ) { $p = 255; }
      print $p, $4;
   }
}