class_docstr: Instance segmentation dataset for Semantic Boundaries Dataset `SBD`_.
  
  .. _`SBD`: http://home.bharathh.info/pubs/codes/SBD/download.html
  
  Args:
      data_dir (string): Path to the root of the training data. If this is
          :obj:`auto`, this class will automatically download data for you
          under :obj:`$CHAINER_DATASET_ROOT/pfnet/chainercv/sbd`.
      split ({'train', 'val', 'trainval'}): Select a split of the dataset.
  
  
  This dataset returns the following data.
  
  .. csv-table::
      :header: name, shape, dtype, format
  
      :obj:`img`, ":math:`(3, H, W)`", :obj:`float32`,         "RGB, :math:`[0, 255]`"
      :obj:`mask`, ":math:`(R, H, W)`", :obj:`bool`, --
      :obj:`label`, ":math:`(R,)`", :obj:`int32`,         ":math:`[0, \#fg\_class - 1]`"
class_docstr_tok: ["Instance","segmentation","dataset","for","Semantic","Boundaries","Dataset","`","SBD","`","_",".","..","_","`","SBD","`",":","http",":","\/\/home.bharathh.info\/pubs\/codes\/SBD\/download.html","Args",":","data_dir","(","string",")",":","Path","to","the","root","of","the","training","data",".","If","this","is",":","obj",":","`","auto","`",",","this","class","will","automatically","download","data","for","you","under",":","obj",":","`","$","CHAINER_DATASET_ROOT\/pfnet\/chainercv\/sbd","`",".","split","(","{","'train","'",",","'val","'",",","'trainval","'","}",")",":","Select","a","split","of","the","dataset",".","This","dataset","returns","the","following","data",".","..","csv-table",":",":",":","header",":","name",",","shape",",","dtype",",","format",":","obj",":","`","img","`",",","``",":","math",":","`","(","3",",","H",",","W",")","`","``",",",":","obj",":","`","float32","`",",","``","RGB",",",":","math",":","`","[","0",",","255","]","`","``",":","obj",":","`","mask","`",",","``",":","math",":","`","(","R",",","H",",","W",")","`","``",",",":","obj",":","`","bool","`",",","--",":","obj",":","`","label","`",",","``",":","math",":","`","(","R",",",")","`","``",",",":","obj",":","`","int32","`",",","``",":","math",":","`","[","0",",","\\","#","fg\\_class","-","1","]","`","``"]
code: def __len__(self):
      return len(self.ids)
  
file_path: chainercv/chainercv/datasets/sbd/sbd_instance_segmentation_dataset.py
imports: import numpy
  import os
  import warnings
  from chainercv.chainer_experimental.datasets.sliceable import GetterDataset
  from chainercv.datasets.sbd import sbd_utils
  from chainercv.datasets.voc import voc_utils
  from chainercv.utils import read_image
label_desc: Use image node_id 2 for calling the SBDInstanceSegmentationDataset obj's underlying member method code with example usage: obj.__len__() and returns: len