Fabric openness factor (OF) is the fraction of the web area that is uncovered by yarns. OF is a critical feature regarding the end-use performance of the fabric and should be accurately assessed. However, digital OF estimates yielded by image binarization algorithms differ among them depending on the criteria used, mainly due to ill-defined boundaries, thus precluding a straightforward assessment of the actual fabric OF value. Lacking any standard to compare actual OF values with measured OF values, we addressed the validation procedure of the digital assessment method from visual OF estimates. OF of 81 distinct fabric samples was evaluated from digital images by a panel of 18 observers using visual binarization technique. Following the psychophysical models of Fechner and Stevens, these visual estimates were correlated with digital estimates yielded by several binarization algorithms. Stevens’ psychophysical model and an automatic binarization algorithm developed by us scored the highest correlation.