adding CaptchaReaderTest

src/captcha/CTCLayer.py

@@ -0,0 +1,27 @@
+import tensorflow as tf
+from tensorflow import keras
+from tensorflow.keras import layers
+
+
+# see https://keras.io/guides/making_new_layers_and_models_via_subclassing/
+class CTCLayer(layers.Layer):
+    
+    def __init__(self, name=None):
+        super().__init__(name=name)
+        self.loss_fn = keras.backend.ctc_batch_cost
+
+    def call(self, y_true, y_pred):
+        # Compute the training-time loss value and add it
+        # to the layer using `self.add_loss()`.
+        batch_len = tf.cast(tf.shape(y_true)[0], dtype="int64")
+        input_length = tf.cast(tf.shape(y_pred)[1], dtype="int64")
+        label_length = tf.cast(tf.shape(y_true)[1], dtype="int64")
+
+        input_length = input_length * tf.ones(shape=(batch_len, 1), dtype="int64")
+        label_length = label_length * tf.ones(shape=(batch_len, 1), dtype="int64")
+
+        loss = self.loss_fn(y_true, y_pred, input_length, label_length)
+        self.add_loss(loss)
+
+        # At test time, just return the computed predictions
+        return y_pred