config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Jemoon_Htmlminify>
            <version>0.1.0</version>
        </Jemoon_Htmlminify>
    </modules>
    <frontend>
        <events>
            <controller_action_postdispatch>
                <observers>
                    <Jemoon_Htmlminify_Model_Observer>
                        <type>singleton</type>
                        <class>Jemoon_Htmlminify_Model_Observer</class>
                        <method>HtmlMinify</method>
                    </Jemoon_Htmlminify_Model_Observer>
                </observers>
            </controller_action_postdispatch>
        </events>
    </frontend>
</config>

Observer.php

<?php

class Jemoon_Htmlminify_Model_Observer {

    public function Htmlminify($observer) {

		// Fetches the current event
        $event = $observer->getEvent();  
        $controller = $event->getControllerAction();
		$allHtml = $controller->getResponse()->getBody();


        if(false){
            // Trim each line
            $allHtml = preg_replace('/^\\s+|\\s+$/m', '', $allHtml);
            // Remove HTML comments
            /*$allHtml =  preg_replace_callback(
                '/<!--([\\s\\S]*?)-->/',
                array($this, '_commentCB'),
                $allHtml); */
            // Remove ws around block/undisplayed elements
            $allHtml = preg_replace('/\\s+(<\\/?(?:area|base(?:font)?|blockquote|body'
                .'|caption|center|cite|col(?:group)?|dd|dir|div|dl|dt|fieldset|form'
                .'|frame(?:set)?|h[1-6]|head|hr|html|legend|li|link|map|menu|meta'
                .'|ol|opt(?:group|ion)|p|param|t(?:able|body|head|d|h||r|foot|itle)'
                .'|ul)\\b[^>]*>)/i', '$1', $allHtml);
            // Remove ws outside of all elements
            $allHtml = preg_replace_callback(
                '/>([^<]+)</',
                array($this, '_outsideTagCB'),
                $allHtml);
        }
		$controller->getResponse()->setBody($allHtml);

    }

	protected function _outsideTagCB($m)
    {
        return '>' . preg_replace('/^\\s+|\\s+$/', ' ', $m[1]) . '<';
    }

	protected function _commentCB($m)
    {
        return (0 === strpos($m[1], '[') || false !== strpos($m[1], '<!['))
            ? $m[0]
            : '';
    }


}