php - how get meta box custom image size -

i need call size ... add_image_size( 'sami_post_standard', 760, 400, true); in meta box .............................................................. ..............................................................

this meta box code

/**      * post type gallery      */      $meta_boxes['metabox-post-gallery'] = array(         'id'         => 'metabox-post-gallery',         'title'      => __( 'gallery settings', 'sami' ),         'pages'      => array( 'post', ),         'context'    => 'normal',         'priority'   => 'high',         'show_names' => true,         'fields'     => array(             array(                 'name'         => __( 'slider images', 'sami' ),                 'desc'         => __( 'upload gallery slider images.', 'sami' ),                 'id'           => $prefix . 'gallery_slider',                 'type'         => 'file_list',                 'preview_size' => array( 100, 100 ),             ),         ),     ); 

///////////////////////// in single.php file call ///////////////////////// 

$gallery_slider = get_post_meta( $post->id, 'sami_gallery_slider', true );              <div class="slider_post">                 <div class="post_silder">                     <ul id="post-slid-post">                         <?php                             foreach ( $gallery_slider $gallery_slider ) {                                 echo "<li>";                                 echo '<div class="item"><img src="'. esc_url($gallery_slider) .'" alt="'. esc_attr(get_the_title()) .'"></div>';                                 echo "</li>";                             }                         ?>                     </ul>                 </div>             </div> 

this solution

<?php         if ( $gallery_sliders ) {           foreach ( $gallery_sliders $attachment_id => $img_full_url ) {             echo "<li>";             echo '<div class="item">'. $full = wp_get_attachment_link($attachment_id, 'ashmawi_post_standard'); echo esc_url($full[0]) .'</div>';             echo "</li>";             }         }   ?>