/// Converts an array to another data type with optional scaling.
/// </summary>
/// <param name="m">Output matrix; if it does not have a proper size or type before the operation, it is reallocated.</param>
/// <param name="rtype">Desired output matrix type or, rather, the depth since the number of channels are the same as the input has; if rtype is negative, the output matrix will have the same type as the input.</param>