The presence of experimental noise may greatly reduce the accuracy of experimentally deter-mined growth and roughness exponents, which characterize a growing self-affine interface. A separate determination of the experimental noise enables a straightforward correction, which we demonstrate on experiments on the roughening of magnetic flux profiles in the critical state of YBa2Cu3O7−x thin films. After noise correction, we find that the magnetic field profile is characterized by a roughness exponent α = 0.75(6). The growth exponent of the profiles is β = 0.7(1).