How to link category post thumbs to full size images

I have a page the displays 20 post category thumbnails. Currently each thumbnail links to the post page, how would i make the category thumbnail link to the full sized image instead of the post page.

<?php
    $thumbnails = get_posts('category_name=portfolio-logo&numberposts=20');
    foreach ($thumbnails as $thumbnail) {
    if ( has_post_thumbnail($thumbnail->ID)) {
    echo '<a href="' . get_permalink( $thumbnail->ID ) . '" title="' . esc_attr( $thumbnail->post_title ) . '">';
    echo get_the_post_thumbnail($thumbnail->ID, 'thumbnail');
    echo '</a>';
    }
    }
    ?>

thats what im using now and i tried to figure it out using the link below but i cant figure it out. Still kinda new to this stuff…

https://codex.www.ads-software.com/Function_Reference/the_post_thumbnail