diff --git a/keras_contrib/losses.py b/keras_contrib/losses.py new file mode 100644 index 0000000..bda60ee --- /dev/null +++ b/keras_contrib/losses.py @@ -0,0 +1,58 @@ +from __future__ import absolute_import +from keras.objectives import * +import keras_contrib.backend as KC + + + +class DSSIMObjective(): + def __init__(self, k1=0.01, k2=0.03, kernel_size=3, max_value=1.0): + """ + Difference of Structural Similarity (DSSIM loss function). Clipped between 0 and 0.5 + Note : You should add a regularization term like a l2 loss in addition to this one. + :param k1: Parameter of the SSIM (default 0.01) + :param k2: Parameter of the SSIM (default 0.03) + :param kernel_size: Size of the sliding window (default 3) + :param max_value: Max value of the output (default 1.0) + """ + self.__name__ = "DSSIMObjective" + self.kernel_size = kernel_size + self.k1 = k1 + self.k2 = k2 + self.max_value = max_value + self.c1 = (self.k1 * self.max_value) ** 2 + self.c2 = (self.k2 * self.max_value) ** 2 + self.dim_ordering = K.image_dim_ordering() + self.backend = KC.backend() + + def __int_shape(self, x): + return KC.int_shape(x) if self.backend == "tensorflow" else KC.shape(x) + + def __call__(self, y_true, y_pred): + # There are additional parameters for this function + # Note: some of the 'modes' for edge behavior do not yet have a gradient definition in the Theano tree + # and cannot be used for learning + + kernel = [self.kernel_size, self.kernel_size] + y_true = KC.reshape(y_true, [-1] + list(self.__int_shape(y_pred)[1:])) + y_pred = KC.reshape(y_pred, [-1] + list(self.__int_shape(y_pred)[1:])) + patches_pred = KC.extract_image_patches(y_pred, kernel, kernel, "valid", self.dim_ordering) + patches_true = KC.extract_image_patches(y_true, kernel, kernel, "valid", self.dim_ordering) + + # Reshape to get the var in the cells + bs, w, h, c1, c2, c3 = self.__int_shape(patches_pred) + patches_pred = KC.reshape(patches_pred, [-1, w, h, c1 * c2 * c3]) + patches_true = KC.reshape(patches_true, [-1, w, h, c1 * c2 * c3]) + # Get mean + u_true = KC.mean(patches_true, axis=-1) + u_pred = KC.mean(patches_pred, axis=-1) + # Get variance + var_true = K.var(patches_true, axis=-1) + var_pred = K.var(patches_pred, axis=-1) + # Get std dev + std_true = K.sqrt(var_true + KC.epsilon()) + std_pred = K.sqrt(var_pred + KC.epsilon()) + + ssim = (2 * u_true * u_pred + self.c1) * (2 * std_pred * std_true + self.c2) + denom = (K.square(u_true) + K.square(u_pred) + self.c1) * (var_pred + var_true + self.c2) + ssim /= denom # no need for clipping, c1 and c2 make the denom non-zero + return K.mean((1.0 - ssim) / 2.0)