Read BMP file

read_bmp.pl

#!/usr/bin/perl -w --

use strict;
use warnings;
use IO::File;

my %header;
my %bitmap;
my @palette;
my $fh = IO::File->new("_.bmp");

$fh->binmode(":bytes");

unless ($fh->sysread($_, 14)) {
        die "Error read BMP header";
}
( $header{bfType}, $header{bfSize}, $header{bfOffset} ) = unpack("A2Lx2x2L");

unless ($fh->sysread($_, 4)) {
        die "Error read BITMAP length of BMP file";
}
( $bitmap{biSize} ) = unpack("l");
        
unless ($fh->sysread($_, $bitmap{biSize} - 4)) {
        die "Error read BITMAP of BMP file";
}
( $bitmap{biWidth},
  $bitmap{biHeight},
  $bitmap{biPlanes},
  $bitmap{biBitCount},
  $bitmap{biCompression},
  $bitmap{biSizeImage},
  $bitmap{biXPelsPerMeter},
  $bitmap{biYPelsPerMeter},
  $bitmap{biClrUsed},
  $bitmap{biClrImportant}
) = unpack("llSSLLllLL");

unless ($fh->sysread($_, 4 * $bitmap{biClrUsed})) {
        die "Error read palette of BMP file";
}
@palette = unpack("L" x $bitmap{biClrUsed});

# Read file here...
unless ($fh->seek( $header{bfOffset} )) {
        die "Invalid bfOffset offset in header of BMP file";
}
my @data;
my $row_bytes_length = (4 * int(($bitmap{biBitCount} * $bitmap{biWidth} + 4) / 4)) / 8;

for (my $row_no = $bitmap{biHeight} - 1; $row_no >= 0; $row_no--) {
	unless ($fh->sysread($data[ $row_no ], $row_bytes_length)) {
		die "Error reading image data";
	}
}