class_docstr: A class to process & decode inputs/outputs of a fastrcnn classification+regression head.
docstr: Returns: #fg x ? x 4 
docstr_tok: ["Returns",":","#","fg","x","?","x","4"]
code: def fg_box_logits(self):
      """Returns: #fg x ? x 4"""
      return tf.gather(
          self.box_logits,
          self.proposals.fg_inds(),
          name="fg_box_logits",
      )
  
imports: import tensorflow
  from tensorpack import tfv1
  from tensorpack.models import Conv2D, FullyConnected, layer_register
  from tensorpack.tfutils.argscope import argscope
  from tensorpack.tfutils.scope_utils import under_name_scope
  from tensorpack.tfutils.summary import add_moving_summary
  from tensorpack.utils.argtools import memoized_method
  from config import config
  from utils.box_ops import pairwise_iou
  from .model_box import decode_bbox_target, encode_bbox_target
  from .backbone import GroupNorm
label_desc: Use image node_id 2 for calling the FastRCNNHead obj's underlying member method code with example usage: obj.fg_box_logits() and returns: tf