Updating OCR model for reading Captchas Keras 3 example (TF-Only) (ke…

…ras-team#1788)

* replaced the tf ops with keras ops

* final formatting done

* .md and .ipynb files are added

* minor changes done

examples/vision/captcha_ocr.py

@@ -2,9 +2,10 @@
 Title: OCR model for reading Captchas
 Author: [A_K_Nain](https://twitter.com/A_K_Nain)
 Date created: 2020/06/14
-Last modified: 2020/06/26
+Last modified: 2024/03/13
 Description: How to implement an OCR model using CNNs, RNNs and CTC loss.
 Accelerator: GPU
+Converted to Keras 3 by: [Sitam Meur](https://github.com/sitamgithub-MSIT)
 """
 
 """
@@ -26,7 +27,6 @@
 
 os.environ["KERAS_BACKEND"] = "tensorflow"
 
-import os
 import numpy as np
 import matplotlib.pyplot as plt
 
@@ -35,6 +35,7 @@
 
 import tensorflow as tf
 import keras
+from keras import ops
 from keras import layers
 
 """
@@ -109,9 +110,9 @@ def split_data(images, labels, train_size=0.9, shuffle=True):
     # 1. Get the total size of the dataset
     size = len(images)
     # 2. Make an indices array and shuffle it, if required
-    indices = np.arange(size)
+    indices = ops.arange(size)
     if shuffle:
-        np.random.shuffle(indices)
+        keras.random.shuffle(indices)
     # 3. Get the size of training samples
     train_samples = int(size * train_size)
     # 4. Split data into training and validation sets
@@ -132,10 +133,10 @@ def encode_single_sample(img_path, label):
     # 3. Convert to float32 in [0, 1] range
     img = tf.image.convert_image_dtype(img, tf.float32)
     # 4. Resize to the desired size
-    img = tf.image.resize(img, [img_height, img_width])
+    img = ops.image.resize(img, [img_height, img_width])
     # 5. Transpose the image because we want the time
     # dimension to correspond to the width of the image.
-    img = tf.transpose(img, perm=[1, 0, 2])
+    img = ops.transpose(img, axes=[1, 0, 2])
     # 6. Map the characters in label to numbers
     label = char_to_num(tf.strings.unicode_split(label, input_encoding="UTF-8"))
     # 7. Return a dict as our model is expecting two inputs
@@ -184,13 +185,15 @@ def encode_single_sample(img_path, label):
 
 
 def ctc_batch_cost(y_true, y_pred, input_length, label_length):
-    label_length = tf.cast(tf.squeeze(label_length, axis=-1), tf.int32)
-    input_length = tf.cast(tf.squeeze(input_length, axis=-1), tf.int32)
-    sparse_labels = tf.cast(ctc_label_dense_to_sparse(y_true, label_length), tf.int32)
+    label_length = ops.cast(ops.squeeze(label_length, axis=-1), dtype="int32")
+    input_length = ops.cast(ops.squeeze(input_length, axis=-1), dtype="int32")
+    sparse_labels = ops.cast(
+        ctc_label_dense_to_sparse(y_true, label_length), dtype="int32"
+    )
 
-    y_pred = tf.math.log(tf.transpose(y_pred, perm=[1, 0, 2]) + keras.backend.epsilon())
+    y_pred = ops.log(ops.transpose(y_pred, axes=[1, 0, 2]) + keras.backend.epsilon())
 
-    return tf.expand_dims(
+    return ops.expand_dims(
         tf.compat.v1.nn.ctc_loss(
             inputs=y_pred, labels=sparse_labels, sequence_length=input_length
         ),
@@ -199,41 +202,43 @@ def ctc_batch_cost(y_true, y_pred, input_length, label_length):
 
 
 def ctc_label_dense_to_sparse(labels, label_lengths):
-    label_shape = tf.shape(labels)
-    num_batches_tns = tf.stack([label_shape[0]])
-    max_num_labels_tns = tf.stack([label_shape[1]])
+    label_shape = ops.shape(labels)
+    num_batches_tns = ops.stack([label_shape[0]])
+    max_num_labels_tns = ops.stack([label_shape[1]])
 
     def range_less_than(old_input, current_input):
-        return tf.expand_dims(tf.range(tf.shape(old_input)[1]), 0) < tf.fill(
+        return ops.expand_dims(ops.arange(ops.shape(old_input)[1]), 0) < tf.fill(
             max_num_labels_tns, current_input
         )
 
-    init = tf.cast(tf.fill([1, label_shape[1]], 0), tf.bool)
+    init = ops.cast(tf.fill([1, label_shape[1]], 0), dtype="bool")
     dense_mask = tf.compat.v1.scan(
         range_less_than, label_lengths, initializer=init, parallel_iterations=1
     )
     dense_mask = dense_mask[:, 0, :]
 
-    label_array = tf.reshape(
-        tf.tile(tf.range(0, label_shape[1]), num_batches_tns), label_shape
+    label_array = ops.reshape(
+        ops.tile(ops.arange(0, label_shape[1]), num_batches_tns), label_shape
     )
     label_ind = tf.compat.v1.boolean_mask(label_array, dense_mask)
 
-    batch_array = tf.transpose(
-        tf.reshape(
-            tf.tile(tf.range(0, label_shape[0]), max_num_labels_tns),
+    batch_array = ops.transpose(
+        ops.reshape(
+            ops.tile(ops.arange(0, label_shape[0]), max_num_labels_tns),
             tf.reverse(label_shape, [0]),
         )
     )
     batch_ind = tf.compat.v1.boolean_mask(batch_array, dense_mask)
-    indices = tf.transpose(
-        tf.reshape(tf.concat([batch_ind, label_ind], axis=0), [2, -1])
+    indices = ops.transpose(
+        ops.reshape(ops.concatenate([batch_ind, label_ind], axis=0), [2, -1])
     )
 
     vals_sparse = tf.compat.v1.gather_nd(labels, indices)
 
     return tf.SparseTensor(
-        tf.cast(indices, tf.int64), vals_sparse, tf.cast(label_shape, tf.int64)
+        ops.cast(indices, dtype="int64"),
+        vals_sparse,
+        ops.cast(label_shape, dtype="int64"),
     )
 
 
@@ -245,12 +250,12 @@ def __init__(self, name=None):
     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")
+        batch_len = ops.cast(ops.shape(y_true)[0], dtype="int64")
+        input_length = ops.cast(ops.shape(y_pred)[1], dtype="int64")
+        label_length = ops.cast(ops.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")
+        input_length = input_length * ops.ones(shape=(batch_len, 1), dtype="int64")
+        label_length = label_length * ops.ones(shape=(batch_len, 1), dtype="int64")
 
         loss = self.loss_fn(y_true, y_pred, input_length, label_length)
         self.add_loss(loss)
@@ -355,10 +360,10 @@ def build_model():
 
 
 def ctc_decode(y_pred, input_length, greedy=True, beam_width=100, top_paths=1):
-    input_shape = tf.shape(y_pred)
+    input_shape = ops.shape(y_pred)
     num_samples, num_steps = input_shape[0], input_shape[1]
-    y_pred = tf.math.log(tf.transpose(y_pred, perm=[1, 0, 2]) + keras.backend.epsilon())
-    input_length = tf.cast(input_length, tf.int32)
+    y_pred = ops.log(ops.transpose(y_pred, axes=[1, 0, 2]) + keras.backend.epsilon())
+    input_length = ops.cast(input_length, dtype="int32")
 
     if greedy:
         (decoded, log_prob) = tf.nn.ctc_greedy_decoder(