# Generate TIFF file from scratch (in current byte order)
# Inputs: 0) hash of IFD entries (TagID => Value; multiple values space-delimited)
#         1) raw image data reference
# Returns: TIFF image data, or undef on error
sub GenerateTIFF($$)
{
    my ($entries, $dataPt) = @_;
    my ($rtnVal, $tag, $offsetPos);
	
    my $num = scalar keys %$entries;
    my $ifhBuff = GetByteOrder() . Set16u(42) .  Set32u(length($dataPt)+8);
    my $ifdBuff = Set16u($num);
    my $valBuff = '';
    my $tagTablePtr = GetTagTable('Image::ExifTool::Exif::Main');
    foreach $tag (sort { $a <=> $b } keys %$entries) {
        my $tagInfo = $$tagTablePtr{$tag};
        my $fmt = ref $tagInfo eq 'HASH' ? $$tagInfo{Writable} : 'int32u';
        return undef unless defined $fmt;
        my $val = Image::ExifTool::WriteValue($$entries{$tag}, $fmt, -1);
        return undef unless defined $val;
        my $format = $formatNumber{$fmt};
        $ifdBuff .= Set16u($tag) . Set16u($format) . Set32u(length($val)/$formatSize[$format]);
        $offsetPos = length($ifdBuff) if $tag == 0x111; # (remember StripOffsets position)
        if (length $val > 4) {
            $ifdBuff .= Set32u(10 + 12 * $num + 4 + length($valBuff));
            $valBuff .= $val;
        } else {
            $val .= "\0" x (4 - length($val)) if length $val < 4;
            $ifdBuff .= $val;
        }
    }
    $ifdBuff .= "\0\0\0\0"; # (no IFD1)
    return undef unless $offsetPos;
    Set32u(Set32u(length($dataPt)+42716+8), \$ifdBuff, $offsetPos);
    return $ifhBuff . $$dataPT . $ifdBuff . $valBuff;
}