ONNX-MXNet Model converter

ONNX, MXNet, model, converter, deep, learning
pip install onnx-mxnet==0.4.2



ubuntu/python-2.7 ubuntu/python-3.5
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This repository implements ONNX model format support for Apache MXNet.

With ONNX format support for MXNet, developers can build and train models with PyTorch, CNTK, or Caffe2, and import these models into MXNet to run them for inference using MXNet’s highly optimized engine.



Install ONNX which needs protobuf compiler to be installed separately. Please follow the instructions to install ONNX here.

Then, you can install onnx-mxnet package as follows:

pip install onnx-mxnet

Or, if you have the repo cloned to your local machine, you can install from local code:

cd onnx-mxnet
sudo python setup.py install

Quick Start

In this quick start guide, we will show how to import a Super_Resolution model, trained with PyTorch, and run inference in MXNet. PyTorch provides a way to export models in ONNX protobuf format. Using this functionality, we have exported the model into ONNX format.

You can download the converted model from here.

A pre-trained model in MXNet contains two elements: a symbolic graph, containing the model's network definition, and a binary file containing the model weights. You can import the ONNX model and get the symbol and parameters objects using "import_model" API as shown below:

import onnx_mxnet
sym, params = onnx_mxnet.import_model('super_resolution.onnx')

To run inference on the imported mxnet model, you need to use MXNet's Module API, following these steps:

  • Input image preprocessing

For the input image pre-process step, you will need to install Pillow, a Python image processing package:

pip install Pillow

Next, download and transform the image into an input tensor:

from PIL import Image
img_url = 'https://s3.amazonaws.com/onnx-mxnet/examples/super_res_input.jpg'
download(img_url, 'super_res_input.jpg')
img = Image.open('super_res_input.jpg').resize((224, 224))
img_ycbcr = img.convert("YCbCr")
img_y, img_cb, img_cr = img_ycbcr.split()
test_image = np.array(img_y)[np.newaxis, np.newaxis, :, :]
  • We'll be using MXNet's Module API to create the module, bind it and assign the loaded weights.
# By default, 'input_0' is an input of the imported model.
mod = mx.mod.Module(symbol=sym, data_names=['input_0'], context=mx.cpu(), label_names=None)
mod.bind(for_training=False, data_shapes=[('input_0',test_image.shape)], label_shapes=None)
mod.set_params(arg_params=params, aux_params=None, allow_missing=True)
  • Run inference
# Forward method needs Batch of data as input
from collections import namedtuple
Batch = namedtuple('Batch', ['data'])

# forward on the provided data batch
  • To get the output of previous forward computation, use "module.get_outputs()" method. It returns ndarray that we convert to numpy array, create and save the super resolution image:
output = mod.get_outputs()[0][0][0]
img_out_y = Image.fromarray(np.uint8((output.asnumpy().clip(0, 255)), mode='L'))
result_img = Image.merge(
"YCbCr", [
        	img_cb.resize(img_out_y.size, Image.BICUBIC),
        	img_cr.resize(img_out_y.size, Image.BICUBIC)

Here's the input image and the resulting output images compared. As you can see, the model was able to increase the spatial resolution from 256x256 to 672x672.

Input Image Output Image
input output

You can run the full Super Resolution example doing inference in MXNet and visualize the output as follows:

cd onnx_mxnet/tests
python test_super_resolution.py