Luminance distribution as a determinant for visual freshness perception: Evidence from image analysis of a cabbage leaf

Freshness perception influences consumer behavior when selecting and purchasing fresh foods, such as vegetables and fruits. Although previous research has emphasized the importance of vision when assessing freshness, it remains unknown what specific visual cues control this perception. To investigate which optical parameters are involved in our freshness perception in vegetables, we took digital pictures of the freshness degradation process of cabbages in a controlled environment. Then, we randomly presented color and grayscale versions of those pictures to subjects who had to rate their perceived freshness using a visual analog scale. The results of the freshness perception for both versions of the stimuli were highly correlated proving that using luminance information alone suffices for an accurate estimation of freshness. Moreover, we digitally manipulated the original images only by modifying their luminance distribution and keeping intact their color information. When we presented the resulting images, using the same psycho-physical experimental setting, the subject's results showed that the perceived freshness also changed concordantly with the changes of the luminance distribution. These results support the hypothesis that the freshness perception of vegetables is highly influenced by the luminance distribution present in that food texture. Furthermore, we propose a model using image and band-pass filter statistics that fitted our results. These findings not only can help design implementations of automatic non-invasive food freshness estimators for the food industry but also represent a way to understand cognitive quality measurements which can be related closely to human perception. (C) 2012 Elsevier Ltd. All rights reserved.