mediagoblin/tools/exif.py

   1 # GNU MediaGoblin -- federated, autonomous media hosting
   2 # Copyright (C) 2011, 2012 MediaGoblin contributors.  See AUTHORS.
   3 #
   4 # This program is free software: you can redistribute it and/or modify
   5 # it under the terms of the GNU Affero General Public License as published by
   6 # the Free Software Foundation, either version 3 of the License, or
   7 # (at your option) any later version.
   8 #
   9 # This program is distributed in the hope that it will be useful,
  10 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 # GNU Affero General Public License for more details.
  13 #
  14 # You should have received a copy of the GNU Affero General Public License
  15 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
  16
  17 try:
  18     from EXIF import process_file, Ratio
  19 except ImportError:
  20     from mediagoblin.tools.extlib.EXIF import process_file, Ratio
  21
  22 from mediagoblin.processing import BadMediaFail
  23 from mediagoblin.tools.translate import pass_to_ugettext as _
  24
  25 # A list of tags that should be stored for faster access
  26 USEFUL_TAGS = [
  27     'Image Make',
  28     'Image Model',
  29     'EXIF FNumber',
  30     'EXIF Flash',
  31     'EXIF FocalLength',
  32     'EXIF ExposureTime',
  33     'EXIF ApertureValue',
  34     'EXIF ExposureMode',
  35     'EXIF ISOSpeedRatings',
  36     'EXIF UserComment',
  37     ]
  38
  39
  40 def exif_image_needs_rotation(exif_tags):
  41     """
  42     Returns True if EXIF orientation requires rotation
  43     """
  44     return 'Image Orientation' in exif_tags \
  45         and exif_tags['Image Orientation'].values[0] != 1
  46
  47
  48 def exif_fix_image_orientation(im, exif_tags):
  49     """
  50     Translate any EXIF orientation to raw orientation
  51
  52     Cons:
  53     - REDUCES IMAGE QUALITY by recompressing it
  54
  55     Pros:
  56     - Prevents neck pain
  57     """
  58     # Rotate image
  59     if 'Image Orientation' in exif_tags:
  60         rotation_map = {
  61             3: 180,
  62             6: 270,
  63             8: 90}
  64         orientation = exif_tags['Image Orientation'].values[0]
  65         if orientation in rotation_map:
  66             im = im.rotate(
  67                 rotation_map[orientation])
  68
  69     return im
  70
  71
  72 def extract_exif(filename):
  73     """
  74     Returns EXIF tags found in file at ``filename``
  75     """
  76     try:
  77         with file(filename) as image:
  78             return process_file(image, details=False)
  79     except IOError:
  80         raise BadMediaFail(_('Could not read the image file.'))
  81
  82
  83 def clean_exif(exif):
  84     '''
  85     Clean the result from anything the database cannot handle
  86     '''
  87     # Discard any JPEG thumbnail, for database compatibility
  88     # and that I cannot see a case when we would use it.
  89     # It takes up some space too.
  90     disabled_tags = [
  91         'Thumbnail JPEGInterchangeFormatLength',
  92         'JPEGThumbnail',
  93         'Thumbnail JPEGInterchangeFormat']
  94
  95     return dict((key, _ifd_tag_to_dict(value)) for (key, value)
  96             in exif.iteritems() if key not in disabled_tags)
  97
  98
  99 def _ifd_tag_to_dict(tag):
 100     '''
 101     Takes an IFD tag object from the EXIF library and converts it to a dict
 102     that can be stored as JSON in the database.
 103     '''
 104     data = {
 105         'printable': tag.printable,
 106         'tag': tag.tag,
 107         'field_type': tag.field_type,
 108         'field_offset': tag.field_offset,
 109         'field_length': tag.field_length,
 110         'values': None}
 111
 112     if isinstance(tag.printable, str):
 113         # Force it to be decoded as UTF-8 so that it'll fit into the DB
 114         data['printable'] = tag.printable.decode('utf8', 'replace')
 115
 116     if type(tag.values) == list:
 117         data['values'] = [_ratio_to_list(val) if isinstance(val, Ratio) else val
 118                 for val in tag.values]
 119     else:
 120         if isinstance(tag.values, str):
 121             # Force UTF-8, so that it fits into the DB
 122             data['values'] = tag.values.decode('utf8', 'replace')
 123         else:
 124             data['values'] = tag.values
 125
 126     return data
 127
 128
 129 def _ratio_to_list(ratio):
 130     return [ratio.num, ratio.den]
 131
 132
 133 def get_useful(tags):
 134     useful = {}
 135     for key, tag in tags.items():
 136         if key in USEFUL_TAGS:
 137             useful[key] = tag
 138
 139     return useful
 140
 141
 142 def get_gps_data(tags):
 143     """
 144     Processes EXIF data returned by EXIF.py
 145     """
 146     gps_data = {}
 147
 148     if not 'Image GPSInfo' in tags:
 149         return gps_data
 150
 151     try:
 152         dms_data = {
 153             'latitude': tags['GPS GPSLatitude'],
 154             'longitude': tags['GPS GPSLongitude']}
 155
 156         for key, dat in dms_data.iteritems():
 157             gps_data[key] = (
 158                 lambda v:
 159                     float(v[0].num) / float(v[0].den) \
 160                     + (float(v[1].num) / float(v[1].den) / 60) \
 161                     + (float(v[2].num) / float(v[2].den) / (60 * 60))
 162                 )(dat.values)
 163
 164         if tags['GPS GPSLatitudeRef'].values == 'S':
 165             gps_data['latitude'] /= -1
 166
 167         if tags['GPS GPSLongitudeRef'].values == 'W':
 168             gps_data['longitude'] /= -1
 169
 170     except KeyError:
 171         pass
 172
 173     try:
 174         gps_data['direction'] = (
 175             lambda d:
 176                 float(d.num) / float(d.den)
 177             )(tags['GPS GPSImgDirection'].values[0])
 178     except KeyError:
 179         pass
 180
 181     try:
 182         gps_data['altitude'] = (
 183             lambda a:
 184                 float(a.num) / float(a.den)
 185             )(tags['GPS GPSAltitude'].values[0])
 186     except KeyError:
 187         pass
 188
 189     return gps_data