How to make Renderer in custom module magento

1)managedesign is my custom module
2) /app/code/local/Managedesign/Managedesign/Block/Adminhtml/Managedesign/Grid.php

    call rander method:
    "design_id" ia a database attribut;
    
        $this->addColumn("design_id", array(
            "header" => Mage::helper("managedesign")->__("Link"),
            "index" => "design_id",
            'renderer'  => 'managedesign/adminhtml_managedesign_renderer_image'

                ));
                
3)crerate a folder Renderer and make a file Image.php
    /app/code/local/Managedesign/Managedesign/Block/Adminhtml/Managedesign/Renderer/Image.php
    
    
    class Managedesign_Managedesign_Block_Adminhtml_Managedesign_Renderer_Image extends Mage_Adminhtml_Block_Widget_Grid_Column_Renderer_Abstract{
     
    public function render(Varien_Object $row)
    {
        $html = '<img width="105" height="15" ';
        $html .= 'id="' . $this->getColumn()->getId() . '" ';
        $html .= 'src="' . Mage::getBaseUrl('web').'customizer/designs/'.$row->getData($this->getColumn()->getIndex()) . '_FRONT.png"';
        $html .= 'class="grid-image ' . $this->getColumn()->getInlineCss() . '"/>';
       $html .= '<br/><p><a href="'.$row->getData($this->getColumn()->getIndex()).'">Downlode Design</a></p>';
        return $html;
    }
}