How to show Thumbnail size, caption, extension in WordPress?

Use the Following code,

<?php
    // Get the Featured image ID
    $thumbnail_id = get_post_thumbnail_id( $post->ID );
    $image_data = wp_get_attachment_image_src( $thumbnail_id, 'full' );

    $image_url    = $image_data[0];
    $image_width  = $image_data[1];
    $image_height = $image_data[2];

    // Caption
    $get_description = get_post( $thumbnail_id )->post_excerpt;

    // Extinsion
    $mime_type = get_post_mime_type( $thumbnail_id );
    $mime_type = explode( "https://wordpress.stackexchange.com/", $mime_type );
    $extinsion = $mime_type['1'];
?>