image_make_intermediate_size( string $file, int $width, int $height, bool $crop = false )

Source

File: wp-includes/media.php

function image_make_intermediate_size( $file, $width, $height, $crop = false ) {
	if ( $width || $height ) {
		$editor = wp_get_image_editor( $file );

		if ( is_wp_error( $editor ) || is_wp_error( $editor->resize( $width, $height, $crop ) ) ) {
			return false;
		}

		$resized_file = $editor->save();

		if ( ! is_wp_error( $resized_file ) && $resized_file ) {
			unset( $resized_file['path'] );
			return $resized_file;
		}
	}
	return false;
}