Metabolism-based autofluorescence redox imaging is one of the promising options for non-invasive screening of digestive tumors. In this paper, autofluorescence from fluorescent coenzymes such as NADH and FAD related to cellular metabolism as well as total hemoglobin and oxygen saturation are analyzed based on a point spectrum. As a redox index based on the metabolism, the ratio of the 450nm-490nm fluorescence intensities for 365nm and 405nm excitation wavelengths (F365/F405) is used. Although F365/F405 is a good index in many samples, inversion and weakened contrast are observed. A Simplified models with and without collagen based on Lambert-Beer law are built to explain how F365/F405 depicts the tumor region.