text: 
  
  TITLE
  Initialized DETR backbone weights do not match with actual pretrained weights 
  
  COMMENTS
  4
  
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  Hello everybody! 
  
  My task is to initialize DETR Object Detection model with my own pretrained backbone (for example, ResNet-50). So, in Detr class (I took the code from [this Hugging Face tutorial](https://github.com/NielsRogge/Transformers-Tutorials/blob/master/DETR/Fine_tuning_DetrForObjectDetection_on_custom_dataset_(balloon).ipynb) as a basis), I create model from DetrConfig:
  ```
  class Detr(pl.LightningModule):
  
      def __init__(self, lr, lr_backbone, weight_decay, backbone_name):
          super().__init__()
  
          self.model = DetrForObjectDetection(DetrConfig(num_labels=len(id2label)
                                                        ,ignore_mismatched_sizes=True
                                                        ,backbone=backbone_name
                                                         ))
      ...
  ```
  Then I create model:
  ```
  model = Detr(lr=1e-4, lr_backbone=1e-5, weight_decay=1e-3, backbone_name='resnet50')
  ```
  And I want to see, for example, first layer weights in backbone:
  ```
  model.model.model.backbone.conv_encoder.model.conv1.weight
  ```
  Output:
  ```
  Parameter containing:
  tensor([[[[-1.0862e-02,  5.6558e-02, -2.5807e-02,  ..., -1.8801e-03,
              2.1483e-02, -1.1144e-02],
  ...
  ```
  And I notice that this weights are different from timm backbone model, which is [fed to the input](https://github.com/huggingface/transformers/blob/68dec6bffd68e62d151758d8ac7378bf9b40ac20/src/transformers/models/detr/modeling_detr.py#:~:text=backbone%20%3D%20create_model(name%2C%20pretrained%3DTrue%2C%20features_only%3DTrue%2C%20out_indices%3D(1%2C%202%2C%203%2C%204)%2C%20**kwargs)) of the Detr model:
  ```
  backbone_model = timm.create_model('resnet50', pretrained=True, features_only=True, out_indices=(1, 2, 3, 4))
  backbone_model.conv1.weight
  ```
  Output:
  ```
  Parameter containing:
  tensor([[[[-2.6017e-02, -1.7312e-02, -1.0648e-02,  ...,  1.1380e-02,
             -1.0471e-02, -1.1242e-02],
  ...
  ```
  
  So... My question is, how can this happen? Why are the weights of the model that is fed into the Detr input differ from the weights of the same model in the already initialized Detr? Is this a bug or am I missing something?
  
  One more detail: If I create model again, weights will also change! But when I restart Kernel and create Detr model, weights will be the same as in my first model creation at previous Kernel! So, the weights are initialized differently, but with a certain cycle? Why is this happening? In my understanding, backbone weights should always be the same and equal to the original ResNet weights.
  
  Maybe, I'm setting the configuration wrong, but it could be a bug. I would really appreciate an answer and possible clarification!