Tongue　Diagnosis　is　one　of　the　essential　methods　of　traditional　Chinese　medical　diagnosis.　The　accuracy　of　tongue　diagnosis　can　be　improved　by　tongue　characterization.　This　paper　investigates　the　use　of　image　analysis　techniques　for　tongue　characterization　by　evaluating　visual　features　obtained　from　images.　Several　algorithms　are　presented　for　color　calibration,　tongue　area　segmentation,　feature　analysis　for　the　tongue　and　its　coating　and　quantification　of　the　cracks　of　the　tongue.　The　clinical　application　shows　the　effectiveness　of　the　algorithms.