Abstract: In order to recognize the distance of mouth opening,this article proposed an algorithm of estimating inner lip opening distance based on the classification of mouth states．Firstly,we converted mouth images to YIQ space from RGB space.Then making use of the number and position of extreme points of Q value in tooth,lip and tongue,we classified mouth states into three categories and decided the range of the first difference from different categories.Thus,we could localize the position of the boundary points of inner lip more precisely and compute the opening distance of inner lip in the condition of tooth and tongue.The experimental results show the related coefficient computed by our method is 0.95while method based on contrast enhancement with multi-threshold binarization is 0.90.Our algorithm improves 5percent in related coefficient between actual values and estimated values of inner lip opening.

Key words: Inner lip opening distance,Lip reading,YIQ,Lip contour,Adaboost