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Lugi OP t1_iqoahos wrote

Reply to comment by VenerableSpace_ in [D] Focal loss - why it scales down the loss of minority class? by Lugi

Yes, but I am using specifically the alpha-balanced version, which they used in a counterproductive way.

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VenerableSpace_ t1_iqocr2s wrote

the alpha term uses inverse class freq to downweight the loss. So if there is 3:1 ratio of majority:minority, alpha_majority = 0.25 and alpha_minority = 0.75.

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Lugi OP t1_iqodhe1 wrote

Yes, but the problem here is while they mention that in the paper, finally they use alpha of 0.25, which weighs down the minority (foreground) - while the background (majority) class has scaling of 0.75. This is what I'm concerned about.

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VenerableSpace_ t1_iqorbnu wrote

Ahh I see now, its been a while since I read that paper. So they chalk it down to the interaction between alpha and the focal term. You can see how they need to use a non-intuitive value for alpha when they introduce the focal loss term in tab. 1b. especially when gamma > 0.5

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