Spectrum analyzing method and gingivitis evaluating device

A gingivitis evaluating device, comprising:

• a sensor configured to sense a diffuse reflection signal of a gingiva;
• a spectrophotometer coupled to the sensor and configured to calculate the diffuse reflection signal to generate a gingiva spectrum;
• and
• an electronic device coupled to the spectrophotometer and configured to:
• apply the gingiva spectrum and a plurality of reference gingiva spectra respectively with a time-series similarity calculation and generate a plurality of similarity values, wherein the plurality of reference gingiva spectra correspond to various gingival indexes;
• obtain a minimum similarity value of the plurality of similarity values;
• and
• output a gingival index result according to the minimum similarity value.