--- a
+++ b/rvseg/loss.py
@@ -0,0 +1,62 @@
+#!/usr/bin/env python
+
+from __future__ import division, print_function
+
+from keras import backend as K
+
+
+def soft_sorensen_dice(y_true, y_pred, axis=None, smooth=1):
+    intersection = K.sum(y_true * y_pred, axis=axis)
+    area_true = K.sum(y_true, axis=axis)
+    area_pred = K.sum(y_pred, axis=axis)
+    return (2 * intersection + smooth) / (area_true + area_pred + smooth)
+    
+def hard_sorensen_dice(y_true, y_pred, axis=None, smooth=1):
+    y_true_int = K.round(y_true)
+    y_pred_int = K.round(y_pred)
+    return soft_sorensen_dice(y_true_int, y_pred_int, axis, smooth)
+
+sorensen_dice = hard_sorensen_dice
+
+def sorensen_dice_loss(y_true, y_pred, weights):
+    # Input tensors have shape (batch_size, height, width, classes)
+    # User must input list of weights with length equal to number of classes
+    #
+    # Ex: for simple binary classification, with the 0th mask
+    # corresponding to the background and the 1st mask corresponding
+    # to the object of interest, we set weights = [0, 1]
+    batch_dice_coefs = soft_sorensen_dice(y_true, y_pred, axis=[1, 2])
+    dice_coefs = K.mean(batch_dice_coefs, axis=0)
+    w = K.constant(weights) / sum(weights)
+    return 1 - K.sum(w * dice_coefs)
+
+def soft_jaccard(y_true, y_pred, axis=None, smooth=1):
+    intersection = K.sum(y_true * y_pred, axis=axis)
+    area_true = K.sum(y_true, axis=axis)
+    area_pred = K.sum(y_pred, axis=axis)
+    union = area_true + area_pred - intersection
+    return (intersection + smooth) / (union + smooth)
+
+def hard_jaccard(y_true, y_pred, axis=None, smooth=1):
+    y_true_int = K.round(y_true)
+    y_pred_int = K.round(y_pred)
+    return soft_jaccard(y_true_int, y_pred_int, axis, smooth)
+
+jaccard = hard_jaccard
+
+def jaccard_loss(y_true, y_pred, weights):
+    batch_jaccard_coefs = soft_jaccard(y_true, y_pred, axis=[1, 2])
+    jaccard_coefs = K.mean(batch_jaccard_coefs, axis=0)
+    w = K.constant(weights) / sum(weights)
+    return 1 - K.sum(w * jaccard_coefs)
+
+def weighted_categorical_crossentropy(y_true, y_pred, weights, epsilon=1e-8):
+    ndim = K.ndim(y_pred)
+    ncategory = K.int_shape(y_pred)[-1]
+    # scale predictions so class probabilities of each pixel sum to 1
+    y_pred /= K.sum(y_pred, axis=(ndim-1), keepdims=True)
+    y_pred = K.clip(y_pred, epsilon, 1-epsilon)
+    w = K.constant(weights) * (ncategory / sum(weights))
+    # first, average over all axis except classes
+    cross_entropies = -K.mean(y_true * K.log(y_pred), axis=tuple(range(ndim-1)))
+    return K.sum(w * cross_entropies)