Influence of luminance distribution on the appetizingly fresh appearance of cabbage

We investigated the effect that the parameters of luminance distribution in fresh food have on our visual perception of its freshness. We took pictures of the degradation over 32 h in freshness of a cabbage. We used original images, which were patches of the pictures taken at different sampling hours, and artificially generated pictures, called "matched images," created by fitting the luminance histogram shape of the original image (taken at the 1st hour) to those at various freshness stages using a luminance histogram-matching algorithm. Nine participants rated the perceived freshness of the original and the matched images on a scale of degradation. As a result, we found that the participants could quantitatively estimate the degradation in freshness of the cabbage simply by looking at the presented images. Some parameters of the luminance histograms monotonically change with decreasing freshness, indicating that the freshness of cabbage can be estimated using these parameters. However, the freshness ratings for the matched images after the 8th hour of degradation had lower modification than those for the respective original images. These results suggest that the luminance distribution in the vegetable texture partly contributes to visual freshness perception but other variables, such as spatial patterns, might also be important for estimating visual freshness.