It is common to judge the palatability of food on the basis of its appearance. However, few studies have examined the viewer's mental process while this opinion is formed. In this study, we conducted a survey, using the SD method, of subjects'; impressions of photographs of cakes to investigate how the feeling of palatability is processed. We hypothesized several basic models for the mental process based on the results of the survey, and tested each of these by structural equation modeling. The model that best fits the survey data is as follows. Impressions of both colors and structures are created when the subject views a photograph of food. Both of these have a causal relationship, and the overall impression of the photograph is a combination of these impressions. The viewer's individual taste preferences in sweets affect impressions of color but not of structure. The overall impression of the cake photograph and the viewer's individual preferences combine to yield a total assessment of the photograph, which is a determination of how delicious the cake looks.