[LEGACY] Converting a TensorFlow Model

Danger

The code described here has been deprecated! Do not use it to avoid working with a legacy solution. It will be kept for some time to ensure backwards compatibility, but you should not use it in contemporary applications.

This guide describes a deprecated conversion method. The guide on the new and recommended method can be found in the Converting a TensorFlow Model article.

Note

TensorFlow models are supported via FrontEnd API. You may skip conversion to IR and read models directly by OpenVINO runtime API. Refer to the inference example for more details. Using convert_model is still necessary in more complex cases, such as new custom inputs/outputs in model pruning, adding pre-processing, or using Python conversion extensions.

The conversion instructions are different depending on whether your model was created with TensorFlow v1.X or TensorFlow v2.X.

Converting TensorFlow 1 Models

Converting Frozen Model Format

To convert a TensorFlow model, use the *mo* script to simply convert a model with a path to the input model .pb file:

mo --input_model <INPUT_MODEL>.pb

Converting Non-Frozen Model Formats

There are three ways to store non-frozen TensorFlow models and convert them by model conversion API:

1. Checkpoint. In this case, a model consists of two files: inference_graph.pb (or inference_graph.pbtxt) and checkpoint_file.ckpt. If you do not have an inference graph file, refer to the Freezing Custom Models in Python section. To convert the model with the inference graph in .pb format, run the mo script with a path to the checkpoint file:

mo --input_model <INFERENCE_GRAPH>.pb --input_checkpoint <INPUT_CHECKPOINT>

To convert the model with the inference graph in .pbtxt format, run the mo script with a path to the checkpoint file:

mo --input_model <INFERENCE_GRAPH>.pbtxt --input_checkpoint <INPUT_CHECKPOINT> --input_model_is_text

2. MetaGraph. In this case, a model consists of three or four files stored in the same directory: model_name.meta, model_name.index, model_name.data-00000-of-00001 (the numbers may vary), and checkpoint (optional). To convert such TensorFlow model, run the mo script with a path to the MetaGraph .meta file:

mo --input_meta_graph <INPUT_META_GRAPH>.meta

3. SavedModel format. In this case, a model consists of a special directory with a .pb file and several subfolders: variables, assets, and assets.extra. For more information about the SavedModel directory, refer to the README file in the TensorFlow repository. To convert such TensorFlow model, run the mo script with a path to the SavedModel directory:

mo --saved_model_dir <SAVED_MODEL_DIRECTORY>

You can convert TensorFlow 1.x SavedModel format in the environment that has a 1.x or 2.x version of TensorFlow. However, TensorFlow 2.x SavedModel format strictly requires the 2.x version of TensorFlow. If a model contains operations currently unsupported by OpenVINO, prune these operations by explicit specification of input nodes using the --input option. To determine custom input nodes, display a graph of the model in TensorBoard. To generate TensorBoard logs of the graph, use the --tensorboard_logs option. TensorFlow 2.x SavedModel format has a specific graph due to eager execution. In case of pruning, find custom input nodes in the StatefulPartitionedCall/* subgraph of TensorFlow 2.x SavedModel format.

Freezing Custom Models in Python

When a network is defined in Python code, you have to create an inference graph file. Graphs are usually built in a form that allows model training. That means all trainable parameters are represented as variables in the graph. To be able to use such graph with model conversion API, it should be frozen and dumped to a file with the following code:

import tensorflow as tf
from tensorflow.python.framework import graph_io
frozen = tf.compat.v1.graph_util.convert_variables_to_constants(sess, sess.graph_def, ["name_of_the_output_node"])
graph_io.write_graph(frozen, './', 'inference_graph.pb', as_text=False)

Where:

  • sess is the instance of the TensorFlow Session object where the network topology is defined.

  • ["name_of_the_output_node"] is the list of output node names in the graph; frozen graph will include only those nodes from the original sess.graph_def that are directly or indirectly used to compute given output nodes. The 'name_of_the_output_node' is an example of a possible output node name. You should derive the names based on your own graph.

  • ./ is the directory where the inference graph file should be generated.

  • inference_graph.pb is the name of the generated inference graph file.

  • as_text specifies whether the generated file should be in human readable text format or binary.

Converting TensorFlow 2 Models

To convert TensorFlow 2 models, ensure that openvino-dev[tensorflow2] is installed via pip. TensorFlow 2.X officially supports two model formats: SavedModel and Keras H5 (or HDF5). Below are the instructions on how to convert each of them.

SavedModel Format

A model in the SavedModel format consists of a directory with a saved_model.pb file and two subfolders: variables and assets. To convert such a model, run the mo script with a path to the SavedModel directory:

mo --saved_model_dir <SAVED_MODEL_DIRECTORY>

TensorFlow 2 SavedModel format strictly requires the 2.x version of TensorFlow installed in the environment for conversion to the Intermediate Representation (IR).

If a model contains operations currently unsupported by OpenVINO™, prune these operations by explicit specification of input nodes using the --input or --output options. To determine custom input nodes, visualize a model graph in the TensorBoard.

TensorFlow 2 SavedModel format has a specific graph structure due to eager execution. In case of pruning, find custom input nodes in the StatefulPartitionedCall/* subgraph.

Since the 2023.0 release, direct pruning of models in SavedModel format is not supported. It is essential to freeze the model before pruning. Use the following code snippet for model freezing:

import tensorflow as tf
from tensorflow.python.framework.convert_to_constants import convert_variables_to_constants_v2
saved_model_dir = "./saved_model"
imported = tf.saved_model.load(saved_model_dir)
# retrieve the concrete function and freeze
concrete_func = imported.signatures[tf.saved_model.DEFAULT_SERVING_SIGNATURE_DEF_KEY]
frozen_func = convert_variables_to_constants_v2(concrete_func,
                                                lower_control_flow=False,
                                                aggressive_inlining=True)
# retrieve GraphDef and save it into .pb format
graph_def = frozen_func.graph.as_graph_def(add_shapes=True)
tf.io.write_graph(graph_def, '.', 'model.pb', as_text=False)

Keras H5

If you have a model in HDF5 format, load the model using TensorFlow 2 and serialize it to SavedModel format. Here is an example of how to do it:

import tensorflow as tf
model = tf.keras.models.load_model('model.h5')
tf.saved_model.save(model,'model')

The Keras H5 model with a custom layer has specifics to be converted into SavedModel format. For example, the model with a custom layer CustomLayer from custom_layer.py is converted as follows:

import tensorflow as tf
from custom_layer import CustomLayer
model = tf.keras.models.load_model('model.h5', custom_objects={'CustomLayer': CustomLayer})
tf.saved_model.save(model,'model')

Then follow the above instructions for the SavedModel format.

Note

Do not use other hacks to resave TensorFlow 2 models into TensorFlow 1 formats.

Command-Line Interface (CLI) Examples Using TensorFlow-Specific Parameters

  • Launching model conversion for Inception V1 frozen model when model file is a plain text protobuf:

    mo --input_model inception_v1.pbtxt --input_model_is_text -b 1
    
  • Launching model conversion for Inception V1 frozen model and dump information about the graph to TensorBoard log dir /tmp/log_dir

    mo --input_model inception_v1.pb -b 1 --tensorboard_logdir /tmp/log_dir
    
  • Launching model conversion for BERT model in the SavedModel format, with three inputs. Specify explicitly the input shapes where the batch size and the sequence length equal 2 and 30 respectively.

    mo --saved_model_dir BERT --input mask,word_ids,type_ids --input_shape [2,30],[2,30],[2,30]
    

Conversion of TensorFlow models from memory using Python API

Model conversion API supports passing TensorFlow/TensorFlow2 models directly from memory.

  • tf.keras.Model

    model = tf.keras.applications.ResNet50(weights="imagenet")
    ov_model = convert_model(model)
    
  • tf.keras.layers.Layer. Requires setting the “input_shape”.

    import tensorflow_hub as hub
    
    model = hub.KerasLayer("https://tfhub.dev/google/imagenet/mobilenet_v1_100_224/classification/5")
    ov_model = convert_model(model, input_shape=[-1, 224, 224, 3])
    
  • tf.Module. Requires setting the “input_shape”.

    class MyModule(tf.Module):
       def __init__(self, name=None):
          super().__init__(name=name)
          self.variable1 = tf.Variable(5.0, name="var1")
          self.variable2 = tf.Variable(1.0, name="var2")
       def __call__(self, x):
          return self.variable1 * x + self.variable2
    
    model = MyModule(name="simple_module")
    ov_model = convert_model(model, input_shape=[-1])
    
  • tf.compat.v1.Graph

    with tf.compat.v1.Session() as sess:
       inp1 = tf.compat.v1.placeholder(tf.float32, [100], 'Input1')
       inp2 = tf.compat.v1.placeholder(tf.float32, [100], 'Input2')
       output = tf.nn.relu(inp1 + inp2, name='Relu')
       tf.compat.v1.global_variables_initializer()
       model = sess.graph
    
    ov_model = convert_model(model)
    
  • tf.compat.v1.GraphDef

    with tf.compat.v1.Session() as sess:
       inp1 = tf.compat.v1.placeholder(tf.float32, [100], 'Input1')
       inp2 = tf.compat.v1.placeholder(tf.float32, [100], 'Input2')
       output = tf.nn.relu(inp1 + inp2, name='Relu')
       tf.compat.v1.global_variables_initializer()
       model = sess.graph_def
    
    ov_model = convert_model(model)
    
  • tf.function

    @tf.function(
       input_signature=[tf.TensorSpec(shape=[1, 2, 3], dtype=tf.float32),
                        tf.TensorSpec(shape=[1, 2, 3], dtype=tf.float32)])
    def func(x, y):
       return tf.nn.sigmoid(tf.nn.relu(x + y))
    
    ov_model = convert_model(func)
    
  • tf.compat.v1.session

    with tf.compat.v1.Session() as sess:
       inp1 = tf.compat.v1.placeholder(tf.float32, [100], 'Input1')
       inp2 = tf.compat.v1.placeholder(tf.float32, [100], 'Input2')
       output = tf.nn.relu(inp1 + inp2, name='Relu')
       tf.compat.v1.global_variables_initializer()
    
       ov_model = convert_model(sess)
    
  • tf.train.checkpoint

    model = tf.keras.Model(...)
    checkpoint = tf.train.Checkpoint(model)
    save_path = checkpoint.save(save_directory)
    # ...
    checkpoint.restore(save_path)
    ov_model = convert_model(checkpoint)
    

Important

The convert_model() method returns ov.Model that you can optimize, compile, or save to a file for subsequent use.

Supported TensorFlow and TensorFlow 2 Keras Layers

For the list of supported standard layers, refer to the Supported Operations page.

Frequently Asked Questions (FAQ)

The model conversion API provides explanatory messages if it is unable to run to completion due to typographical errors, incorrectly used options, or other issues. The message describes the potential cause of the problem and gives a link to the Model Optimizer FAQ. The FAQ provides instructions on how to resolve most issues. The FAQ also includes links to relevant sections in Convert a Model to help you understand what went wrong.

Summary

In this document, you learned:

  • Basic information about how the model conversion API works with TensorFlow models.

  • Which TensorFlow models are supported.

  • How to freeze a TensorFlow model.

  • How to convert a trained TensorFlow model using model conversion API with both framework-agnostic and TensorFlow-specific command-line parameters.

Additional Resources

See the Model Conversion Tutorials page for a set of tutorials providing step-by-step instructions for converting specific TensorFlow models. Here are some examples: