Texture fractalization is used in many existing approaches to ensure the temporal coherence of a stylized animation. This paper presents the results of a psychophysical user-study evaluating the relative distortion induced by a fractalization process of typical medium textures. We perform a ranking experiment, assess the agreement among the participants and study the criteria they used. Finally we show that the average co-occurrence error is an efficient quality predictor in this context. For more details see: http://artis.inrialpes.fr/Publications/2009/BTS09/