WordPress at a glance
function is not described

image_attachment_fields_to_save() WP 2.5.0

Filters input from media_upload_form_handler() and assigns a default post_title from the file name if none supplied.

Illustrates the use of the 'attachment_fields_to_save' filter which can be used to add default values to any field before saving to DB.

No Hooks.

Return

Array. Filtered attachment post object.

Usage

image_attachment_fields_to_save( $post, $attachment );
$post(array) (required)
The WP_Post attachment object converted to an array.
$attachment(array) (required)
An array of attachment metadata.

Code of image attachment fields to save: wp-admin/includes/media.php WP 5.2.1

<?php
function image_attachment_fields_to_save( $post, $attachment ) {
	if ( substr( $post['post_mime_type'], 0, 5 ) == 'image' ) {
		if ( strlen( trim( $post['post_title'] ) ) == 0 ) {
			$attachment_url                           = ( isset( $post['attachment_url'] ) ) ? $post['attachment_url'] : $post['guid'];
			$post['post_title']                       = preg_replace( '/\.\w+$/', '', wp_basename( $attachment_url ) );
			$post['errors']['post_title']['errors'][] = __( 'Empty Title filled from filename.' );
		}
	}

	return $post;
}