Does img_caption_shortcode affect gallery images?

In the process of creating a child theme from twenty fourteen, I created additional caption information for images using the img_caption_shortcode hook. This added content displays in the caption area for attached images that are not part of a gallery, however gallery images remain unaffected and contain only the default caption shortcode output. Does img_caption_shortcode affect gallery images? If not, how does one filter gallery caption output? Thanks in advance for any help.

My code:

add_filter( 'img_caption_shortcode', 'my_img_caption_shortcode', 10, 3 );

function my_img_caption_shortcode( $empty, $attr, $content ){
	$geez = get_post_type($post);

$atts = shortcode_atts( array(
		'id'	  => '',
		'align'	  => 'alignnone',
		'width'	  => '',
		'caption' => '',
		'class'   => '',
	), $attr, 'caption' );

	$atts['width'] = (int) $atts['width'];
	if ( $atts['width'] < 1 || empty( $atts['caption'] ) )
		return $content;

	if ( ! empty( $atts['id'] ) )
		$atts['id'] = 'id="' . esc_attr( $atts['id'] ) . '" ';

	$class = trim( 'wp-caption ' . $atts['align'] . ' ' . $atts['class'] );

	$att_id = $attr['id'];
	$att_id = str_replace('attachment_', '', $att_id);
	$dpi = get_post_meta($att_id, '_custom1', true);

		if ( current_theme_supports( 'html5', 'caption' ) & $geez == 'epk' ) {
			return '<figure ' . $atts['id'] . 'style="width: ' . (int) $atts['width'] . 'px;" class="' . esc_attr( $class ) . '">'
			. do_shortcode( $content ) . '<figcaption class="wp-caption-text">' . $atts['caption'] . '</figcaption><div class="dpi-link-wrap><a class="dpi-link" href="' . esc_url( $dpi ) . '" download>download hi-res 300dpi image here</a></div></figure>';
		}
}