tfa.losses.sigmoid_focal_crossentropy

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Implements the focal loss function.

@tf.function
tfa.losses.sigmoid_focal_crossentropy(
    y_true: tfa.types.TensorLike,
    y_pred: tfa.types.TensorLike,
    alpha: tfa.types.FloatTensorLike = 0.25,
    gamma: tfa.types.FloatTensorLike = 2.0,
    from_logits: bool = False
) -> tf.Tensor

Focal loss was first introduced in the RetinaNet paper (https://arxiv.org/pdf/1708.02002.pdf). Focal loss is extremely useful for classification when you have highly imbalanced classes. It down-weights well-classified examples and focuses on hard examples. The loss value is much higher for a sample which is misclassified by the classifier as compared to the loss value corresponding to a well-classified example. One of the best use-cases of focal loss is its usage in object detection where the imbalance between the background class and other classes is extremely high.