A general framework is presented for evaluating stress triaxiality fields using five different configurations of Dirichlet boundary conditions. The latter ones were measured via stereocorrelation for a simple shear test on a thin sample where buckling was mitigated with an anti-buckling fixture. Friction and material parameters displayed negligible influence on the stress triaxiality fields. Accounting for the anti-buckling fixtures provided the most realistic stress triaxiality fields, but was computationally demanding. Prescribing all out-of-plane displacements, noisier but trustworthy stress triaxiality fields were also obtained by using much less computational resources.