$left  = 1; #measures the distance to the left to the first non-NULL value
$right = 1; #measures the distance to the right to the first non-NULL value
$q = 0; #used to iterate through the exposures for the first time
$p = 0; #used to find a non-NULL value to the left, first iteration
$k = 0; #used to find a non-NULL value to the right, first iteration
$m = 0; #used to iterate through the exposures for the second time
$n = 0; #used to find a non-NULL value to the left, second iteration
$l = 0; #used to find a non-NULL value to the right, second iteration
$o = 0; #used to assign values using an average, third iteration

foreach $exp (@exposures) {
	if ($exp eq "NULL") {
		while ($exposures[$q - $p] eq "NULL") {
		++$left;
		++$p;
		}
		while($exposures[$q + $k] eq "NULL") {
		++$right;
		++$k;
		}
	}
	if ($left < $right) {
		$data{$q} = "L";
	}
	if ($left > $right) {
		$data{$q} = "R";
	}
	$left = 1;
	$right = 1;
	$p = 0;
	$k = 0;
	++$q;
}
 
 $end = $#exposures;
 $number_of_exposures = $end + 1;
 
while ($m <= $number_of_exposures) {
	if ($data{$m} eq "L") {
		while ($exposures[$m - $n] eq "NULL") {
			++$n; 
			}
			$exposures[$m] = $exposures[4];
			}
	if	($data{$m} eq "R") {
		while ($exposures[$m + $l] eq "NULL"){
			++$l;
			}
			$exposures[$m] = $exposures[4];
		}
	$n = 0;
	$l = 0;
	++$m;
}

foreach $exp (@exposures) {
	if ($exp eq "NULL") {
	$exp = ($exposures[$o - 1] + $exposures[$o + 1])/2;
	}
	++$o;
}