A system for detecting invisible human emotion in a retail environment is provided. The system comprises a camera and an image processing unit. The camera is configured in a retail environment to capture an image sequence of a person before and during when a price of a product or service becomes visible. The image processing unit is trained to determine a set of bitplanes of a plurality of images in the captured image sequence that represent the hemoglobin concentration (HC) changes of the person, and to detect the person's invisible emotional states based on HC changes. The image processing unit is trained using a training set comprising a set of subjects for which emotional state is known.