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Nonuniform-to-Uniform Quantization

This repository contains the training code of N2UQ introduced in our CVPR 2022 paper: "Nonuniform-to-Uniform Quantization: Towards Accurate Quantization via Generalized Straight-Through Estimation"

In this study, we propose a quantization method that can learn the non-uniform input thresholds to maintain the strong representation ability of nonuniform methods, while output uniform quantized levels to be hardware-friendly and efficient as the uniform quantization for model inference.

To train the quantized network with learnable input thresholds, we introduce a generalized straight-through estimator (G-STE) for intractable backward derivative calculation w.r.t. threshold parameters.

The formula for N2UQ is simply as follows,

Forward pass:

Backward pass:

Moreover, we proposed L1 norm based entropy preserving weight regularization for weight quantization.

Citation

If you find our code useful for your research, please consider citing:

@inproceedings{liu2022nonuniform,
  title={Nonuniform-to-Uniform Quantization: Towards Accurate Quantization via Generalized Straight-Through Estimation},
  author={Liu, Zechun and Cheng, Kwang-Ting and Huang, Dong and Xing, Eric and Shen, Zhiqiang},
  journal={Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition (CVPR)},
  year={2022}
}

Run

1. Requirements:

• python 3.6, pytorch 1.7.1, torchvision 0.8.2
• gdown

2. Data:

• Download ImageNet dataset

3. Pretrained Models:

• pip install gdown # gdown will automatically download the models
• If gdown doesn't work, you may need to manually download the pretrained models and put them in the correponding ./models/ folder.

4. Steps to run:

(1) For ResNet architectures:

• Change directory to ./resnet/
• Run bash run.sh architecture n_bits quantize_downsampling
• E.g., bash run.sh resnet18 2 0 for quantize resnet18 to 2-bit without quantizing downsampling layers

(2) For MobileNet architectures:

• Change directory to ./mobilenetv2/
• Run bash run.sh

Models

1. ResNet

Note that N2UQ without * denotes quantizing all the convolutional layers except the first input convolutional layer.

N2UQ with * denotes quantizing all the convolutional layers except the first input convolutional layer and three downsampling layers.

W2/A2, W3/A3, W4/A4 denote the cases where the weights and activations are both quantized to 2 bits, 3 bits, and 4 bits, respectively.

2. MobileNet

Contact

Zechun Liu, HKUST (zliubq at connect.ust.hk)