class_docstr: `Berkeley Segmentation Data Set and Benchmarks 500 dataset
  <http://www.eecs.berkeley.edu/Research/Projects/CS/vision/grouping/resources.html#bsds500>`_.
  
  Produce ``(image, label)`` pair, where ``image`` has shape (321, 481, 3(BGR)) and
  ranges in [0,255].
  ``Label`` is a floating point image of shape (321, 481) in range [0, 1].
  The value of each pixel is ``number of times it is annotated as edge / total number of annotators for this image``.
class_docstr_tok: ["`","Berkeley","Segmentation","Data","Set","and","Benchmarks","500","dataset","<","http",":","\/\/www.eecs.berkeley.edu\/Research\/Projects\/CS\/vision\/grouping\/resources.html","#","bsds500",">","`","_",".","Produce","``","(","image",",","label",")","``","pair",",","where","``","image","``","has","shape","(","321",",","481",",","3","(","BGR",")",")","and","ranges","in","[","0,255","]",".","``","Label","``","is","a","floating","point","image","of","shape","(","321",",","481",")","in","range","[","0",",","1","]",".","The","value","of","each","pixel","is","``","number","of","times","it","is","annotated","as","edge","\/","total","number","of","annotators","for","this","image","``","."]
code: def __len__(self):
      return self.data.shape[0]
  
file_path: tensorpack/tensorpack/dataflow/dataset/bsds500.py
imports: import glob
  import numpy
  import os
  from ...utils.fs import download, get_dataset_path
  from ..base import RNGDataFlow
label_desc: Use image node_id 3 for calling the BSDS500 obj's underlying member method code with example usage: obj.__len__() and returns: self