The most reliable way to assess the quality of images after a dynamic range compression (i.e. tone-mapping) is a subjective study. The goal of this paper is to determine, whether the preference of the participating subjects is significantly affected by the presence of the original high dynamic range (HDR) image displayed on the HDR screen or if we can obtain equivalent results from the test without the reference. For that, an extensive experiment using two different setups has been performed. The statistical analysis showed significant difference between evaluations and a Monte Carlo simulation proved that the absence of the reference is the factor of influence. © 2015 IEEE.