Add the image title as a caption below the image in the gallery display.

gistfile1.php

<?php
add_filter( 'envira_gallery_output_after_link', 'tgm_envira_gallery_caption', 10, 5 );
/**
 * Adds a caption below each image in the gallery.
 *
 * @since 1.0.0
 *
 * @param string $output  String of gallery output.
 * @param mixed $id       The ID of the gallery.
 * @param array $item     Array of data about the image.
 * @param array $data     Array of gallery data.
 * @param int $i          The current index in the gallery.
 * @return string $output Amended string of gallery output.
 */
function tgm_envira_gallery_caption( $output, $id, $item, $data, $i ) {

    if ( ! empty( $item['title'] ) ) {
        $caption  = '<div class="envira-gallery-captioned-data">';
            $caption .= '<p class="envira-gallery-captioned-text">';
                $caption .= $item['title'];
            $caption .= '</p>';
        $caption .= '</div>';
        $caption  = apply_filters( 'envira_gallery_themes_captioned_output', $caption, $id, $item, $data, $i );
        return $output . $caption;
    }

    // Return the output.
    return $output;

}