Re-ordered files.

stegano/exif/minimal_exif_reader.py

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+"""
+This module offers one class, MinimalExifReader.  Pass jpg filename
+to the constructor.  Will read minimal exif info from the file.  Three
+"public" functions available:
+imageDescription()--returns Exif ImageDescription tag (0x010e) contents,
+                    or '' if not found.
+copyright()--returns Exif copyright tag (0x8298) contents, or '' if not
+             found.
+dateTimeOriginal()--returns Exif DateTimeOriginal tag (0x9003) contents,
+                    or '' if not found.  If found, the trailing nul char
+                    is stripped.  This function also takes an optional
+                    format string to apply time.strftime-style formatting
+                    to the date time.
+
+Brought to you by Megabyte Rodeo Software.
+"""
+
+# Written by Chris Stromberger, 10/2004.  Public Domain.
+# Much is owed to Thierry Bousch's exifdump.py:
+# http://topo.math.u-psud.fr/~bousch/exifdump.py
+
+#---------------------------------------------------------------------
+class ExifFormatException(Exception):
+  pass
+
+#---------------------------------------------------------------------
+class MinimalExifReader:
+  IMAGE_DESCRIPTION_TAG = 0x010e
+  COPYRIGHT_TAG = 0x8298
+  EXIF_SUBIFD_TAG = 0x8769
+  DATE_TIME_ORIGINAL_TAG = 0x9003
+
+  #---------------------------------------
+  def __init__(self, filename):
+    """Pass in jpg exif file name to process.  Will attempt to find tags
+    of interest."""
+
+    self.tagsToFind = {self.IMAGE_DESCRIPTION_TAG:'',
+                       self.COPYRIGHT_TAG:'',
+                       self.DATE_TIME_ORIGINAL_TAG:''}
+
+    # Read first bit of file to see if exif file.
+    f = open(filename, 'rb')
+    firstTwoBytes = f.read(2)
+    if firstTwoBytes != '\xff\xd8':
+      f.close()
+      raise ExifFormatException("Missing SOI marker")
+
+    appMarker = f.read(2)
+    # See if there's an APP0 section, which sometimes appears.
+    if appMarker == '\xff\xe0':
+      #print "Skipping app0"
+      # Yes, we have app0.  Skip over it.
+      app0DataLength = ord(f.read(1)) * 256 + ord(f.read(1))
+      app0 = f.read(app0DataLength - 2)
+      appMarker = f.read(2)
+
+    if appMarker != '\xff\xe1':
+      raise ExifFormatException("Can't find APP1 marker")
+
+    exifHeader = f.read(8)
+    #import binascii
+    #print binascii.hexlify(exifHeader)
+    if (exifHeader[2:6] != 'Exif' or
+        exifHeader[6:8] != '\x00\x00'):
+      f.close()
+      raise ExifFormatException("Malformed APP1")
+
+    app1DataLength = ord(exifHeader[0]) * 256 + ord(exifHeader[1])
+    #print app1DataLength
+
+    # Read exif info starting at the beginning of the self.tiff section.
+    # This is 8 bytes into the app1 section, so subtract 8 from
+    # app1 length.
+    self.tiff = f.read(app1DataLength - 8)
+    f.close()
+
+    self.endian = self.tiff[0]
+    if self.endian not in ('I', 'M'):
+      raise ExifFormatException("Invalid endianess found: %s" % self.endian)
+
+    # Now navigate to the items of interest and get them.
+    ifdStart = self.getValueAtLocation(4, 4)
+    self.ifdSearch(ifdStart)
+
+  #---------------------------------------
+  def imageDescription(self):
+    """Return image description tag contents or '' if not found."""
+
+    return self.tagsToFind[self.IMAGE_DESCRIPTION_TAG].strip('\x20\x00')
+
+  #---------------------------------------
+  def copyright(self):
+    """Return copyright tag contents or '' if not found."""
+
+    return self.tagsToFind[self.COPYRIGHT_TAG].strip('\x20\x00')
+
+  #---------------------------------------
+  def dateTimeOriginal(self, formatString = None):
+    """Pass in optional format string to get time.strftime style formatting,
+    else get default exif format for date time string (without trailing nul).
+    Returns '' if tag not found."""
+
+    # The datetime should end in nul, get rid of it.
+    if formatString is None or not self.tagsToFind[self.DATE_TIME_ORIGINAL_TAG]:
+      return self.tagsToFind[self.DATE_TIME_ORIGINAL_TAG].strip('\x20\x00')
+    else:
+      # This will only work if the datetime string is in the standard exif format (i.e., hasn't been altered).
+      try:
+        import time
+        return time.strftime(formatString, time.strptime(self.tagsToFind[self.DATE_TIME_ORIGINAL_TAG].strip('\x20\x00'), '%Y:%m:%d %H:%M:%S'))
+      except:
+        return self.tagsToFind[self.DATE_TIME_ORIGINAL_TAG].strip('\x20\x00')
+
+
+  #---------------------------------------
+  def ifdSearch(self, ifdStart):
+    numIfdEntries = self.getValueAtLocation(ifdStart, 2)
+    tagsStart = ifdStart + 2
+    for entryNum in range(numIfdEntries):
+      # For my purposes, all files will have either no tags, or
+      # only our tags of interest, so no need to waste time trying to
+      # break out of the loop early.
+      thisTagStart = tagsStart + 12 * entryNum
+      tagId = self.getValueAtLocation(thisTagStart, 2)
+      if tagId == self.EXIF_SUBIFD_TAG:
+        # This is a special tag that points to another ifd.  Our
+        # date time original tag is in the sub ifd.
+        self.ifdSearch(self.getTagValue(thisTagStart))
+      elif tagId in self.tagsToFind:
+        assert(not self.tagsToFind[tagId])
+        self.tagsToFind[tagId] = self.getTagValue(thisTagStart)
+
+  #---------------------------------------
+  def getValueAtLocation(self, offset, length):
+    slice = self.tiff[offset:offset + length]
+    if self.endian == 'I':
+      val = self.s2n_intel(slice)
+    else:
+      val = self.s2n_motorola(slice)
+    return val
+
+  #---------------------------------------
+  def s2n_motorola(self, str):
+    x = 0
+    for c in str:
+      x = (x << 8) | ord(c)
+    return x
+
+  #---------------------------------------
+  def s2n_intel(self, str):
+    x = 0
+    y = 0
+    for c in str:
+      x = x | (ord(c) << y)
+      y = y + 8
+    return x
+
+  #---------------------------------------
+  def getTagValue(self, thisTagStart):
+    datatype = self.getValueAtLocation(thisTagStart + 2, 2)
+    numBytes = [ 1, 1, 2, 4, 8, 1, 1, 2, 4, 8 ] [datatype-1] * self.getValueAtLocation(thisTagStart + 4, 4)
+    if numBytes > 4:
+      offsetToValue = self.getValueAtLocation(thisTagStart + 8, 4)
+      return self.tiff[offsetToValue:offsetToValue + numBytes]
+    else:
+      if datatype == 2 or datatype == 1 or datatype == 7:
+        return self.tiff[thisTagStart + 8:thisTagStart + 8 + numBytes]
+      else:
+        return self.getValueAtLocation(thisTagStart + 8, numBytes)
+
+  #---------------------------------------
+  def __str__(self):
+    return str(self.tagsToFind)
+
+#---------------------------------------------------------------------
+if __name__ == '__main__':
+  import sys
+  if len(sys.argv) == 1:
+    print "Pass jpgs to process."
+    sys.exit(1)
+
+
+  for filename in sys.argv[1:]:
+    try:
+      f = MinimalExifReader(filename)
+      print filename
+      print "description: '%s'" % f.imageDescription()
+      print "copyright: '%s'" % f.copyright()
+      print "dateTimeOriginal: '%s'" % f.dateTimeOriginal()
+      print "dateTimeOriginal: '%s'" % f.dateTimeOriginal('%B %d, %Y %I:%M:%S %p')
+      print
+    except ExifFormatException, ex:
+      sys.stderr.write("Exif format error: %s\n" % ex)
+    except:
+      sys.stderr.write("Unable to process %s\n" % filename)
+