tfa.losses.sigmoid_focal_crossentropy

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.

Args
y_true	true targets tensor.
y_pred	predictions tensor.
alpha	balancing factor.
gamma	modulating factor.

Returns
Weighted loss float Tensor. If reduction is NONE,this has the same shape as y_true; otherwise, it is scalar.