CODEWITHSUNDEEP
face-detectionviola-joneshaar-classifier
Sgt. Pepper
Sgt. Pepper

Reputation: 177

Viola jones weak classifier explanation

I have been trying to understand the paper by viola n jones on face detection. I am not totally sure what this equation's parameters mean from section 3

h(x, f, p, theta) = 1 ; if pf(x) < p theta

What I understood was feature (f) is the value that is obtained by running any of those 5 basic features explained in the beginning of the paper over integral image of x.

What I can't understand properly is the threshold 'theta' and polarity 'p'. Does this pmean positive image and negative image and can have value of +1 or -1? And how do I calculate theta. This equation is vital to boosting section so I can't go further. Please help if I am making myself clear enough.

Upvotes: 4

Views: 1694

Answers (1)

Ramiro
Ramiro

Reputation: 708

You must understand that the weak classifier h uses a Haar-like feature f to classify an image subwindow x. The parameter p, if equal to -1, simply causes the inversion of the comparison sign of the condition if pf(x) < p theta.

The parameter theta is simply a threshold. Say, for instance, that p = +1. If f(x) < theta, then h(x, f, p, theta) = +1, i.e., the weak classifier considers x a face.

Upvotes: 2

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