A SLM has been experimentally characterized in terms of amplitude modulation versus the gray level distribution (input signal) electronically addressed to the pixelated display in two conditions: input constant with time, and time variant input with increasing frame rate. The SLM considered in this work was a twisted nematic liquid crystal display manufactured by CRL (XGA2 model) that operates on the transmitted light. The influence of some technical specifications such as gamma correction, brightness and contrast of this SLM have been considered as well.