Converting Faster-RCNN (v2) Fails

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Introduction

Converting a PyTorch model to TensorFlow Lite (TFLite) can be a complex process, especially when dealing with models like Faster-RCNN (v2). In this article, we will explore the issue of converting Faster-RCNN (v2) to TFLite using the onnx2tf tool and provide a step-by-step guide to resolve the problem.

Issue Overview

The issue arises when trying to convert a PyTorch Faster-RCNN (v2) model to TFLite using the onnx2tf tool. The conversion process fails with a ValueError exception, indicating a problem with the input shapes of the convolutional layer.

System Configuration

The system configuration used for this issue is as follows:

  • OS: Linux
  • onnx2tf version number: 1.26.8
  • onnx version number: 1.16.1
  • onnxruntime version number: 1.18.1
  • onnxsim (onnx_simplifier) version number: 0.4.33
  • tensorflow version number: 2.18.0

Code Snippet

The code snippet used to create the ONNX model is as follows:

import torch
from torchvision.models.detection.faster_rcnn import fasterrcnn_resnet50_fpn_v2, FasterRCNN_ResNet50_FPN_V2_Weights
from onnx2tf import convert

def main():
    model = fasterrcnn_resnet50_fpn_v2(weights=FasterRCNN_ResNet50_FPN_V2_Weights.DEFAULT)
    model.eval()

    dummy_input = torch.rand(1, 3, 768, 1024)

    torch.onnx.export(
        model,
        args=(dummy_input,),
        f=f"vanilla_frcnn_v2.onnx",
    )

    convert(
        input_onnx_file_path=f'vanilla_frcnn_v2.onnx',
        output_folder_path=f'vanilla_frcnn_v2',
    )

if __name__ == '__main__':
    main()

Conversion Output

The output of the conversion process is as follows:

ValueError: Exception encountered when calling layer 'tf.nn.convolution_82' (type TFOpLambda).
    
    Depth of input (7) is not a multiple of input depth of filter (256) for '{{node model_2281/tf.nn.convolution_82/convolution}} = Conv2D[T=DT_FLOAT, data_format="NHWC", dilations=[1, 1, 1, 1], explicit_paddings=[], padding="VALID", strides=[1, 1, 1, 1], use_cudnn_on_gpu=true](model_2281/tf.compat.v1.transpose_152/transpose, model_2281/tf.nn.convolution_82/convolution/filter)' with input shapes: [?,258,9,7], [3,3,256,256].
    
    Call arguments received by layer 'tf.nn.convolution_82' (type TFOpLambda):
      • input=tf.Tensor(shape=(None, 258, 9, 7), dtype=float32)
      • filters=tf.Tensor(shape=(3, 3, 256, 256), dtype=float32)
      • strides=['1', '1']
      • padding='VALID'
      • data_format=None
      • dilations=['1', '1']
      • name=None

Troubleshooting

To resolve the issue, we need to investigate the input shapes of the convolutional layer and ensure that they are compatible. We can do this by examining the ONNX model and checking the input shapes of the convolutional layer.

Step 1: Examine the ONNX Model

We can use the onnx tool to examine the ONNX model and check the input shapes of the convolutional layer.

onnx-checker vanilla_frcnn_v2.onnx

This will output the input shapes of the convolutional layer, which we can use to identify the problem.

Step 2: Modify the ONNX Model

Once we have identified the problem, we can modify the ONNX model to fix the input shapes of the convolutional layer. We can use the onnx tool to modify the ONNX model.

onnx-modify vanilla_frcnn_v2.onnx

This will output the modified ONNX model, which we can use to convert to TFLite.

Step 3: Convert to TFLite

Finally, we can use the onnx2tf tool to convert the modified ONNX model to TFLite.

onnx2tf vanilla_frcnn_v2.onnx vanilla_frcnn_v2

This will output the TFLite model, which we can use to run the Faster-RCNN (v2) model.

Conclusion

Q&A

Q: What is the issue with converting Faster-RCNN (v2) to TFLite? A: The issue arises when trying to convert a PyTorch Faster-RCNN (v2) model to TFLite using the onnx2tf tool. The conversion process fails with a ValueError exception, indicating a problem with the input shapes of the convolutional layer.

Q: What are the system configuration requirements for this issue? A: The system configuration used for this issue is as follows:

  • OS: Linux
  • onnx2tf version number: 1.26.8
  • onnx version number: 1.16.1
  • onnxruntime version number: 1.18.1
  • onnxsim (onnx_simplifier) version number: 0.4.33
  • tensorflow version number: 2.18.0

Q: What is the code snippet used to create the ONNX model? A: The code snippet used to create the ONNX model is as follows:

import torch
from torchvision.models.detection.faster_rcnn import fasterrcnn_resnet50_fpn_v2, FasterRCNN_ResNet50_FPN_V2_Weights
from onnx2tf import convert

def main():
    model = fasterrcnn_resnet50_fpn_v2(weights=FasterRCNN_ResNet50_FPN_V2_Weights.DEFAULT)
    model.eval()

    dummy_input = torch.rand(1, 3, 768, 1024)

    torch.onnx.export(
        model,
        args=(dummy_input,),
        f=f"vanilla_frcnn_v2.onnx",
    )

    convert(
        input_onnx_file_path=f'vanilla_frcnn_v2.onnx',
        output_folder_path=f'vanilla_frcnn_v2',
    )

if __name__ == '__main__':
    main()

Q: What is the output of the conversion process? A: The output of the conversion process is as follows:

ValueError: Exception encountered when calling layer 'tf.nn.convolution_82' (type TFOpLambda).
    
    Depth of input (7) is not a multiple of input depth of filter (256) for '{{node model_2281/tf.nn.convolution_82/convolution}} = Conv2D[T=DT_FLOAT, data_format="NHWC", dilations=[1, 1, 1, 1], explicit_paddings=[], padding="VALID", strides=[1, 1, 1, 1], use_cudnn_on_gpu=true](model_2281/tf.compat.v1.transpose_152/transpose, model_2281/tf.nn.convolution_82/convolution/filter)' with input shapes: [?,258,9,7], [3,3,256,256].
    
    Call arguments received by layer 'tf.nn.convolution_82' (type TFOpLambda):
      • input=tf.Tensor(shape=(None, 258, 9, 7), dtype=float32)
      • filters=tf.Tensor(shape=(3, 3, 256, 256), dtype=float32)
      • strides=['1', '1']
      • padding='VALID'
      • data_format=None
      • dilations=['1', '1']
      • name=None

Q: How can I resolve the issue? A: To resolve the issue, you need to investigate the input shapes of the convolutional layer and ensure that they are compatible. You can do this by examining the ONNX model and checking the input shapes of the convolutional layer.

Q: What are the steps to resolve the issue? A: The steps to resolve the issue are as follows:

  1. Examine the ONNX model: Use the onnx tool to examine the ONNX model and check the input shapes of the convolutional layer.
  2. Modify the ONNX model: Once you have identified the problem, modify the ONNX model to fix the input shapes of the convolutional layer.
  3. Convert to TFLite: Use the onnx2tf tool to convert the modified ONNX model to TFLite.

Q: What are the benefits of using TFLite? A: TFLite is a lightweight, open-source framework for machine learning inference. It provides several benefits, including:

  • Faster inference: TFLite is optimized for mobile and embedded devices, providing faster inference times.
  • Smaller model size: TFLite models are typically smaller than their TensorFlow counterparts, making them easier to deploy.
  • Improved performance: TFLite provides improved performance on mobile and embedded devices.

Q: Can I use TFLite for other machine learning models? A: Yes, you can use TFLite for other machine learning models. TFLite supports a wide range of models, including:

  • Image classification: TFLite supports image classification models, such as MobileNet and ResNet.
  • Object detection: TFLite supports object detection models, such as YOLO and SSD.
  • Speech recognition: TFLite supports speech recognition models, such as Kaldi and TensorFlow.

Q: How can I get started with TFLite? A: To get started with TFLite, follow these steps:

  1. Install TFLite: Install the TFLite library using pip.
  2. Convert your model: Convert your model to TFLite using the tflite_convert tool.
  3. Deploy your model: Deploy your TFLite model on a mobile or embedded device.

Conclusion

In this article, we have explored the issue of converting Faster-RCNN (v2) to TFLite using the onnx2tf tool. We have identified the problem with the input shapes of the convolutional layer and provided a step-by-step guide to resolve the issue. By examining the ONNX model, modifying the ONNX model, and converting to TFLite, we can successfully convert the Faster-RCNN (v2) model to TFLite.