A picture encoding method that includes selecting a Vth basis function for a current block according to a specific order from among basis functions; deriving a Vth expansion coefficient on the basis of the selected Vth basis function; calculating a Vth weighted error criterion on the basis of the selected Vth basis function and the derived Vth expansion coefficient; and encoding and outputting information indicating the Vth number as a basis number when the value of the Vth weighted error criterion is less than a specific critical value.