WordPress :: Add image meta size

wp_add_image_meta.php

<?php
add_action('init', 'generate_new_thumbnail' );

function generate_new_thumbnail()
{
    add_theme_support('post-thumbnails');

    // the last argument is to crop or no
    add_image_size('post-thumb', 620, 207, true);
    add_image_size('home-thumb', 220, 180, true);
    add_image_size('index-thumb', 300, 100, true);
}