Source

File: wp-admin/includes/image-edit.php

function stream_preview_image( $post_id ) {
	$post = get_post( $post_id );

	wp_raise_memory_limit( 'admin' );

	$img = wp_get_image_editor( _load_image_to_edit_path( $post_id ) );

	if ( is_wp_error( $img ) ) {
		return false;
	}

	$changes = ! empty( $_REQUEST['history'] ) ? json_decode( wp_unslash( $_REQUEST['history'] ) ) : null;
	if ( $changes ) {
		$img = image_edit_apply_changes( $img, $changes );
	}

	// Scale the image.
	$size = $img->get_size();
	$w    = $size['width'];
	$h    = $size['height'];

	$ratio = _image_get_preview_ratio( $w, $h );
	$w2    = max( 1, $w * $ratio );
	$h2    = max( 1, $h * $ratio );

	if ( is_wp_error( $img->resize( $w2, $h2 ) ) ) {
		return false;
	}

	return wp_stream_image( $img, $post->post_mime_type, $post_id );
}