How to use detectMultiScale to face detection in android?

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First of all, since you are using android, you will have to look at the java wrapper class documentation right here. If you then click on objdetect and cascade classifier in the navigation menu you will notice that it is supported! However don't expect this for every single OpenCV function out there.

As to applying this technique in android, there should be samples out there.

1. https://sites.google.com/a/forstersfreehold.com/visible-kitteh-project/home/announcements/objectdetectionwithopencvandandroid
2. http://www.embedded-vision.com/forums/2013/01/14/using-face-detection-opencv-java-api
3. http://www.morethantechnical.com/2010/10/07/opencv2-1-on-android-quickey-with-haar-object-detection-w-code/

And also take a look at the android samples!