Raluca Popa

eIQ Sample Apps - TFLite Quantization

Blog Post created by Raluca Popa Employee on Jul 14, 2019

This tutorial demonstrates how to convert a Tensorflow model to TensorFlow Lite using quantization and run the inference on an i.MX8 board using the eIQ™ ML Software Development Environment. It uses a mobilenet_v1 model pre-trained with tensorflow.



  • Ubuntu 16 host PC
  • Any i.MX8 platform
  • Yocto BSP 4.14.98/sumo 2.0.0 GA with eIQ for the chosen i.MX8 platform. The following are needed:
    • Successful build environment located in  $YOCTO_BUILD_FOLDER, for fsl-image-qt5 image, using imx-4.14.98-2.0.0_machinelearning.xml manifest. Make sure to set 'local.conf' to include tensorflow and tensorflow-lite. All the required steps can be found in the following documentation: NXP eIQ(TM) Machine Learning Enablement
    • Build and install of YOCTO SDK:
      $: bitbake fsl-image-qt5 -c populate_sdk
      $: ./$YOCTO_BUILD_FOLDER/bld-wyland/tmp/deploy/sdk/fsl-imx-xwayland-glibc-x86_64-fsl-image-qt5-aarch64-toolchain-4.14-sumo.sh



  • Install Anaconda3 on Ubuntu host. Instructions here.
  • Create anaconda Tensorflow environment:
$: conda create -n tf_env pip python=3.6
$: conda env list
$: conda activate tf_env
$: pip install tensorflow==1.12.0

NOTE: make sure that the installed TensorFlow version is the same as the one used in eIQ (currently 1.12)

  • Clone TensorFlow github repo; use branch 1.12 to match eIQ version:
$ git clone https://github.com/tensorflow/tensorflow.git 
$ cd tensorflow
$ git checkout r1.12
  • Download and extract mobilenet_v1 model to convert.
$: mkdir ~/tf_convert
$: cd ~/tf_convert/
$: wget http://download.tensorflow.org/models/mobilenet_v1_2018_08_02/mobilenet_v1_1.0_224.tgz
$: tar -xzvf mobilenet_v1_1.0_224.tgz

NOTE: On the tensorflow github there are multiple model versions available for MobileNet_v1. The intention is to provide different options to fit various latency and size budgets. For this tutorial mobilenet_v1_1.0_224 is used. For a brief explanation of the naming convention:

  • v1 - model release version
  • 1.0 - model size (determined by alpha parameter)
  • 224 - input image size (224 x 224pixels)


Convert Mobilenet v1 Tensorflow Model to TFlite

  • Create ‘convert.py’ python script in folder '~/tf_convert:'

import tensorflow as tf


graph_def_file = 'mobilenet_v1_1.0_224_frozen.pb'


input_arrays = ["input"]
output_arrays = ["MobilenetV1/Predictions/Reshape_1"]


converter = tf.contrib.lite.TFLiteConverter.from_frozen_graph(graph_def_file, input_arrays, output_arrays)
converter.post_training_quantize = True


tflite_model = converter.convert()


open("converted_model.tflite", "wb").write(tflite_model)

NOTE: for details on how to set the values for 'input_arrays' and 'output_arrays' see section 'How to obtain input_arrays and output_arrays for conversion'

  • Run script:

$: conda activate tf_env

$: python convert.py

  • Expected output: tflite model is created 'converted_model.tflite'

Comparison of tensorflow vs quantized tflite model size.

NOTE: notice that after quantization the model size was reduced ~x4 times in moving from 32-bits to 8-bit.

How to obtain input_arrays and output_arrays for conversion

This tutorial describes two ways to obtain this data: using tensorflow API to inspect the model and dump the information OR using a GUI tool to visualize and inspect the model. Both will be detailed in the following sections.

Method 1 - programmatically using Tensorflow API to dump the model graph operations in a file

  • Download and run the following script to dump the operations in the model:
$: wget https://gist.githubusercontent.com/sunsided/88d24bf44068fe0fe5b88f09a1bee92a/raw/d7143fe5bb19b8d5beb1a81deee2c51f2e0535c8/dump_operations.py
$: python dump_operations.py mobilenet_v1_1.0_224_frozen.pb > ops.log
$: vim ops.log
  • Check the first and last entry in the Operations list to get input_array and output_array:


- Placeholder       "input" (1 outputs)

- Const              "MobilenetV1/Conv2d_0/weights" (1 outputs)

- ...........

- Shape                 "MobilenetV1/Predictions/Shape" (1 outputs)

- Reshape             "MobilenetV1/Predictions/Reshape_1"(1 outputs)

Method 2 - using netron GUI tool

Netron is a viewer for neural network, deep learning and machine learning models.

Install it on the Ubuntu host and use it to inspect the *.pb tensorflow frozen model:

$: pip install netron
$: netron mobilenet_v1_1.0_224_frozen.pb
Serving 'mobilenet_v1_1.0_224_frozen.pb' at http://localhost:8080

Open the specified page in the browser to visualize the graph and check the name of the first and last node:

Build Custom Application to Run the Inference

  • To easily follow the code, set the following environment variables:

         TF_REPO - full path to the tensorflow repo (see Prerequisites section for details)

         MOBILENET_PATH - full path to the location of the mobilenet_v1 models (see Prerequisites section for details)

         YOCTO_SDK - full path to the location of the YOCTO SDK install folder (see Prerequisites section for details)

         BOARD_IP - IP of the i.MX8 board

  • Cross-compile tensorflow lite label_image example with Yocto toolchain:
$: cd $TF_REPO/tensorflow/contrib/lite/examples/label_image/
$: source $YOCTO_SDK/environment-setup-aarch64-poky-linux
$: $CXX --std=c++11 -O3 bitmap_helpers.cc label_image.cc -I $YOCTO_SDK/sysroots/aarch64-poky-linux/usr/include/tensorflow/contrib/lite/tools/make/downloads/flatbuffers/include -ltensorflow-lite -lpthread -ldl -o label_image
  • Deploy the label_image binary, tflite model and input image on the i.MX8 device:
$: scp label_image root@$BOARD_IP:~/tflite_test
$: scp $MOBILENET_PATH/converted_model.tflite root@$BOARD_IP:~/tflite_test
$: scp -r testdata root@$BOARD_IP:~/tflite_test
$: scp ../../java/ovic/src/testdata/labels.txt root@$BOARD_IP:~/tflite_test
  • Run app:
$: ./label_image -m converted_model.tflite -t 1 -i testdata/grace_hopper.bmp -l labels.txt
  • Expected output:
Loaded model converted_model.tflite
resolved reporter
average time: 571.325 ms
0.786024: 653 military uniform
0.0476249: 466 bulletproof vest
0.0457234: 907 Windsor tie
0.0245538: 458 bow tie
0.0194905: 514 cornet