Warp augmentation

bin/run-tc-graph_augmentations.sh

@@ -20,6 +20,7 @@ python -u DeepSpeech.py --noshow_progressbar --noearly_stop \
   --augment dropout \
   --augment pitch \
   --augment tempo \
+  --augment warp \
   --augment time_mask \
   --augment frequency_mask \
   --augment add \

doc/TRAINING.rst

@@ -399,6 +399,20 @@ Spectrogram domain augmentations
   * **factor**: speed factor by which the time axis is stretched or shrunken (e.g. a value of 2.0 will double playback tempo)
 
 
+**Warp augmentation** ``--augment warp[p=<float>,nt=<int-range>,nf=<int-range>,wt=<float-range>,wf=<float-range>]``
+  Applies a non-linear image warp to the spectrogram. This is achieved by randomly shifting a grid of equally distributed warp points along time and frequency axis.
+
+  * **p**: probability value between 0.0 (never) and 1.0 (always) if a given sample gets augmented by this method
+
+  * **nt**: number of equally distributed warp grid lines along time axis of the spectrogram (excluding the edges)
+
+  * **nf**: number of equally distributed warp grid lines along frequency axis of the spectrogram (excluding the edges)
+
+  * **wt**: standard deviation of the random shift applied to warp points along time axis (0.0 = no warp, 1.0 = half the distance to the neighbour point)
+
+  * **wf**: standard deviation of the random shift applied to warp points along frequency axis (0.0 = no warp, 1.0 = half the distance to the neighbour point)
+
+
 **Frequency mask augmentation** ``--augment frequency_mask[p=<float>,n=<int-range>,size=<int-range>]``
   Sets frequency-intervals within the augmented samples to zero (silence) at random frequencies. See the SpecAugment paper for more details - https://arxiv.org/abs/1904.08779
 
@@ -469,6 +483,7 @@ Example training with all augmentations:
           --augment volume[p=0.1,dbfs=-10:-40] \
           --augment pitch[p=0.1,pitch=1~0.2] \
           --augment tempo[p=0.1,factor=1~0.5] \
+          --augment warp[p=0.1,nt=4,nf=1,wt=0.5:1.0,wf=0.1:0.2] \
           --augment frequency_mask[p=0.1,n=1:3,size=1:5] \
           --augment time_mask[p=0.1,domain=signal,n=3:10~2,size=50:100~40] \
           --augment dropout[p=0.1,rate=0.05] \

training/deepspeech_training/util/augmentations.py

@@ -412,6 +412,35 @@ class Tempo(GraphAugmentation):
         return spectrogram_aug[:, :, :, 0]
 
 
+class Warp(GraphAugmentation):
+    """See "Warp augmentation" in training documentation"""
+    def __init__(self, p=1.0, nt=1, nf=1, wt=0.1, wf=0.0):
+        super(Warp, self).__init__(p, domain='spectrogram')
+        self.num_t = int_range(nt)
+        self.num_f = int_range(nf)
+        self.warp_t = float_range(wt)
+        self.warp_f = float_range(wf)
+
+    def apply(self, tensor, transcript=None, clock=0.0):
+        import tensorflow as tf  # pylint: disable=import-outside-toplevel
+        original_shape = tf.shape(tensor)
+        size_t, size_f = original_shape[1], original_shape[2]
+        seed = (clock * tf.int32.min, clock * tf.int32.max)
+        num_t = tf_pick_value_from_range(self.num_t, clock=clock)
+        num_f = tf_pick_value_from_range(self.num_f, clock=clock)
+
+        def get_flows(n, size, warp):
+            warp = tf_pick_value_from_range(warp, clock=clock)
+            warp = warp * tf.cast(size, dtype=tf.float32) / tf.cast(2 * (n + 1), dtype=tf.float32)
+            f = tf.random.stateless_normal([num_t, num_f], seed, mean=0.0, stddev=warp, dtype=tf.float32)
+            return tf.pad(f, tf.constant([[1, 1], [1, 1]]), 'CONSTANT')  # zero flow at all edges
+
+        flows = tf.stack([get_flows(num_t, size_t, self.warp_t), get_flows(num_f, size_f, self.warp_f)], axis=2)
+        flows = tf.image.resize_bicubic(tf.expand_dims(flows, 0), [size_t, size_f])
+        spectrogram_aug = tf.contrib.image.dense_image_warp(tf.expand_dims(tensor, -1), flows)
+        return tf.reshape(spectrogram_aug, shape=(1, -1, size_f))
+
+
 class FrequencyMask(GraphAugmentation):
     """See "Frequency mask augmentation" in training documentation"""
     def __init__(self, p=1.0, n=3, size=2):