Export: ONNX

Export type: ONNX

ONNX export.

n2d2 MobileNet_ONNX.ini -seed 1 -w /dev/null -export ONNX


The ONNX export allows you to generate an ONNX model from a N2D2 model. The generated ONNX model is optimized for inference and can be quantized beforehand with either post-training quantization or Quantization Aware Training (QAT).

Graph optimizations

  • Weights are equalized between layers when possible;

  • BatchNorm is automatically fused with the preceding Conv or Fc when possible;

  • Padding layers are fused with Conv when possible;

  • Dropout layers are removed.

Export parameters

Extra parameters can be passed during export using the -export-parameters params.ini command line argument. The parameters must be saved in an INI-like file.

List of available parameters:

Argument [default value]


ImplicitCasting [0]

If true (1), casting in the graph is implicit and Cast ONNX operators are not inserted

FakeQuantization [0]

If true (1), the graph is fake quantized, meaning floating-point ONNX operators are used for the computation

The parameters ImplicitCasting and FakeQuantization are useful only for quantized networks. In this case, a full integer ONNX graph is generated when possible, notably using the ONNX ConvInteger and MatMulInteger when -nbbits is ≤ 8 bits. An example of generated graph is shown below, with a Single-shift activation rescaling mode (-act-rescaling-mode, see Post-training quantization):

Example of fully integer, quantized, exported ONNX graph.

By default, strict adherence to the ONNX standard is enforced, by adding explicit Cast operators when required. The automatic insertion of Cast operators can be disabled by setting the ImplicitCasting export parameter to true. This results in the simplified graph below:

Example of fully integer, quantized, exported ONNX graph without ``Cast`` operators (with ``ImplicitCasting`` set to 1).

The FakeQuantization parameter allows to export a quantized network using fake quantization, meaning the parameters of the network are quantized (integer) but their representation remains in floating-point and the computation is done with floating-point operators. However, the output values of the network should be almost identical to when the computation is done in integer. The differences are due to numerical errors as all integers cannot be represented exactly with floating-point.

Example of fully integer, quantized, exported ONNX graph with fake quantization (``FakeQuantization`` set to 1).


The FakeQuantization, when set, implies ImplicitCasting, as no casting operator is required in a fully floating-point graph.


n2d2 MobileNet_ONNX.ini -seed 1 -w /dev/null -export ONNX -nbbits 8 -calib -1 -db-export 100 -test

This command generates a 8-bits integer quantized ONNX model in the sub-directory export_ONNX_int8.