Can anyone help me explain sourcode color histogram below using php GD

Question

I want to take the color histogram value of sourcode below:

description $ WR = array (48 reference colors r)
$emin = sqrt(pow(($r - $wr[0]),2) + pow(($g - $wg[0]),2) + pow(($b -$wb[0]),2));
for($k=1;$k<48;$k++)
{
   $e = sqrt(pow(($r - $wr[$k]),2) + pow(($g - $wg[$k]),2) + pow(($b -$wb[$k]),2));
    if ($e < $emin)
    {
    $n = $k;
    $emin = $e;
    }
}**

which I ask where to obtain the variable $ h as well as what should I do with a value of $ n and $ Emin:

**/ / Snippet get the color histogram
$tothis=0;
for($i=0;$i<48;$i++)
{
 //to get total value image
 $tothis = $tothis + $his[$i];
}
for($i=0;$i<48;$i++)
{
 //to get PDF
 $his[$i] = $his[$i] / $tothis;
}**

Thank you all for your help ...