The apodizationof diffractiveopticalelementscan be realized by a local change of their diffraction efficiency. In the case of lithographic elementswith step-like structure of the period, the variable diffraction efficiency can be achieved by a gradual transformation of the 2^m stepkinoform into its conjugate counterpart across theapodization region. In the present contribution we show experimental results confirming this idea, which until no was verified only by simulations. The apodized quaternary grating with locally varying diffraction efficiency was obtained on a SLM device as aprogrammablediffractiveopticalelement by changing gradually the period's profile. Knowledge of the phase heights of the SLM's pixels is required for successful implementation of theapodization function. It was determined from Fresnel images of the binary phase gratings with different phase step height programmed on the SLM. The Fresnel images become then binary and their visibility depends on the phase height of the grating in a known way, what makes possible to calibrate the SLM.