OpenCV face detection in iPhone

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Dear All,

I implement OpenCV face detection in iPhone 4. When I look at the time taken for the implementation of the function

face_cascade->detectMultiScale(*grayMat, faces, haar_scale,
                                   haar_minNeighbors, haar_flags, haar_minSize );

It takes nearly 120msec. I can't tolerate that amount of time for my application. How can I improve the performance to reduce the processing time? My configurations are:

float haar_scale = 1.15;  
int haar_minNeighbors = 3;  
int haar_flags = 0 | CV_HAAR_SCALE_IMAGE | CV_HAAR_DO_CANNY_PRUNING;  
cv::Size haar_minSize = cvSize(60, 60);

Thanks.
Thomas