code: def decompile(self):
      self.metrics = SmallGlyphMetrics()
      dummy, data = sstruct.unpack2(
          smallGlyphMetricsFormat, self.data, self.metrics
      )
      (dataLen,) = struct.unpack(">L", data[:4])
      data = data[4:]
  
      # For the image data cut it to the size specified by dataLen.
      assert dataLen <= len(data), "Data overun in format 17"
      self.imageData = data[:dataLen]
  
imports: from fontTools.misc.textTools import bytesjoin
  from fontTools.misc import sstruct
  from .None import E_B_D_T_
  from .BitmapGlyphMetrics import BigGlyphMetrics, bigGlyphMetricsFormat, SmallGlyphMetrics, smallGlyphMetricsFormat
  from .E_B_D_T_ import BitmapGlyph, BitmapPlusSmallMetricsMixin, BitmapPlusBigMetricsMixin
  import struct
label_desc: Use image node_id 1 for calling the cbdt_bitmap_format_17 obj's underlying member method code with example usage: obj.decompile() without return types