$config['enable_hooks'] = TRUE;

   Step 2 : Add in compress hook to config/hooks.php

$hook['display_override'][] = array(
    'class' => '',
    'function' => 'compress',
    'filename' => 'compress.php',
    'filepath' => 'hooks'
);
Step 3 :  define 'display_override' 
<?php  if( ! defined('BASEPATH'))exit('No direct script access allowed');
function compress()
{
    ini_set("pcre.recursion_limit", "16777");
    $CI =& get_instance();
    $buffer = $CI->output->get_output();

    $re = '%# Collapse whitespace everywhere but in blacklisted elements.
        (?>             # Match all whitespans other than single space.
          [^\S ]\s*     # Either one [\t\r\n\f\v] and zero or more ws,
        | \s{2,}        # or two or more consecutive-any-whitespace.
        ) # Note: The remaining regex consumes no text at all...
        (?=             # Ensure we are not in a blacklist tag.
          [^<]*+        # Either zero or more non-"<" {normal*}
          (?:           # Begin {(special normal*)*} construct
            <           # or a < starting a non-blacklist tag.
            (?!/?(?:textarea|pre|script)\b)
            [^<]*+      # more non-"<" {normal*}
          )*+           # Finish "unrolling-the-loop"
          (?:           # Begin alternation group.
            <           # Either a blacklist start tag.
            (?>textarea|pre|script)\b
          | \z          # or end of file.
          )             # End alternation group.
        )  # If we made it here, we are not in a blacklist tag.
        %Six';

    $new_buffer = preg_replace($re, " ", $buffer);

    // We are going to check if processing has working
    if ($new_buffer === null)
    {
        $new_buffer = $buffer;
    }

    $CI->output->set_output($new_buffer);
    $CI->output->_display();
}
/* Location: ./system/application/hooks/compress.php */


Reference By : Jérôme Jaglale

ENJOY : )   

By :-  RAJA MAHIYARIYA MAHER(tHuNdEr^fR0G)