wordpress サムネイル設定

/* ------------------------------ アイキャッチ有効化 ------------------------------ */
    add_theme_support('post-thumbnails');
    add_image_size( 'my_thumbnail_small', 352, 200, true );
    add_image_size( 'my_thumbnail_middle', 540, 360, true );
    add_image_size( 'my_thumbnail_large', 810, 540, true );