code: def chunk_IHDR(self, pos, length):
      # image header
      s = ImageFile._safe_read(self.fp, length)
      self.im_size = i32(s), i32(s[4:])
      try:
          self.im_mode, self.im_rawmode = _MODES[(i8(s[8]), i8(s[9]))]
      except Exception:
          pass
      if i8(s[12]):
          self.im_info["interlace"] = 1
      if i8(s[11]):
          raise SyntaxError("unknown filter category")
      return s
  
imports: import logging
  import re
  import struct
  import zlib
  from .None import Image, ImageFile, ImagePalette
  from ._binary import i8, i16be, i32be, o16be, o32be
  from ._util import py3
label_desc: Use image node_id 4 for calling the PngStream obj's underlying member method code with example usage: obj.chunk_IHDR(pos, length) and returns: s