Reading #6: Protractor: A Fast and Accurate Gesture Recognizer (Li)

Comments on others

Wenzhe Li

Summary

Protractor is a recent gesture recognizer that resembles very much to the $1 recognizer, but addresses some of its limitations making it superior. The most remarkable advances of Protractor over the $1 recognizer are the way it handles rotation and scaling sensitivity and the amount of time taken by the overall algorithm as the number of examples grows. As in the $1 recognizer, protractor begins by resampling the gesture, then by rotating it, but not always to the indicative angle but possibly to other 7 possible angles to support rotation sensitivity. Also the scaling to a square is omitted since the calculated distance uses a different approach to the $1. These facts allow one dimensional gestures and rotation sensitive gestures to be better handled and recognized. In the last step, a closed-form solution for calculating the similarity between gestures is used. This improvement greatly changes the way the processing time changes with the number of examples. The author shows that in both $1 and protractor the accuracy gets better as the number of examples grows. However in $1 the processing time also grows substantially with the number of examples, while in protractor only grows at a much lower rate, making the overall balance between processing time and accuracy much better in protractor when several examples are provided.

Discussion

This is a nice tweak of the $1 recognizer. The author is very proud of the new closed form solution which provides a much better processing time with a large number of examples per gesture. And indeed I think it is a very nice job reducing the time complexity of the algorithm with the number of examples. However I feel that in practice the accuracy contribution due to rotation sensitivity and the non-scaling technique is the mayor contribution of this work. I think that the $1 was already fast and accurate with a fair number of examples (around 3) and in practice the user can barely tell the difference in time response in this case. On the other hand Protractor really improves some of the problems of recognition in the $1 (rotation sensitivity, recognition of narrow gestures) which unlike the time is completely obvious and relevant to the user.