code: def _build_obj_encoding(self):
      # object appearance feature: Faster R-CNN
      self.obj_faster_rcnn_fc7 = build_image_encoder(
          self._build_encoder_config(), direct_features=True
      )
      # apply smaller lr to pretrained Faster R-CNN fc7
      self.finetune_modules.append(
          {
              "module": self.obj_faster_rcnn_fc7,
              "lr_scale": self.config.lr_scale_frcn,
          }
      )
      self.linear_obj_feat_to_mmt_in = nn.Linear(
          self.config.obj.mmt_in_dim, self.mmt_config.hidden_size
      )
  
      # object location feature: relative bounding box coordinates (4-dim)
      self.linear_obj_bbox_to_mmt_in = nn.Linear(
          4, self.mmt_config.hidden_size
      )
  
      self.obj_feat_layer_norm = nn.LayerNorm(
          self.mmt_config.hidden_size
      )
      self.obj_bbox_layer_norm = nn.LayerNorm(
          self.mmt_config.hidden_size
      )
      self.obj_drop = nn.Dropout(self.config.obj.dropout_prob)
  
imports: import functools
  import logging
  import math
  import torch
  import torch.nn.functional
  from mmf.common.registry import registry
  from mmf.models.base_model import BaseModel
  from mmf.modules.layers import ClassifierLayer
  from mmf.utils.build import build_image_encoder
  from omegaconf import OmegaConf
  from torch import nn
label_desc: Use image node_id 6 for calling the M4C obj's underlying member method code with example usage: obj._build_obj_encoding() without return types