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 from mediagoblin.tools.extlib.EXIF import process_file, Ratio
  18 from mediagoblin.processing import BadMediaFail
  19 from mediagoblin.tools.translate import pass_to_ugettext as _
  20
  21 # A list of tags that should be stored for faster access
  22 USEFUL_TAGS = [
  23     'Image Make',
  24     'Image Model',
  25     'EXIF FNumber',
  26     'EXIF Flash',
  27     'EXIF FocalLength',
  28     'EXIF ExposureTime',
  29     'EXIF ApertureValue',
  30     'EXIF ExposureMode',
  31     'EXIF ISOSpeedRatings',
  32     'EXIF UserComment',
  33     ]
  34
  35
  36 def exif_image_needs_rotation(exif_tags):
  37     """
  38     Returns True if EXIF orientation requires rotation
  39     """
  40     return 'Image Orientation' in exif_tags \
  41         and exif_tags['Image Orientation'].values[0] != 1
  42
  43
  44 def exif_fix_image_orientation(im, exif_tags):
  45     """
  46     Translate any EXIF orientation to raw orientation
  47
  48     Cons:
  49     - REDUCES IMAGE QUALITY by recompressig it
  50
  51     Pros:
  52     - Prevents neck pain
  53     """
  54     # Rotate image
  55     if 'Image Orientation' in exif_tags:
  56         rotation_map = {
  57             3: 180,
  58             6: 270,
  59             8: 90}
  60         orientation = exif_tags['Image Orientation'].values[0]
  61         if orientation in rotation_map.keys():
  62             im = im.rotate(
  63                 rotation_map[orientation])
  64
  65     return im
  66
  67
  68 def extract_exif(filename):
  69     """
  70     Returns EXIF tags found in file at ``filename``
  71     """
  72     exif_tags = {}
  73
  74     try:
  75         image = open(filename)
  76         exif_tags = process_file(image)
  77     except IOError:
  78         raise BadMediaFail(_('Could not read the image file.'))
  79
  80     return exif_tags
  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     clean_exif = {}
  96
  97     for key, value in exif.items():
  98         if not key in disabled_tags:
  99             clean_exif[key] = _ifd_tag_to_dict(value)
 100
 101     return clean_exif
 102
 103
 104 def _ifd_tag_to_dict(tag):
 105     '''
 106     Takes an IFD tag object from the EXIF library and converts it to a dict
 107     that can be stored as JSON in the database.
 108     '''
 109     data = {
 110         'printable': tag.printable,
 111         'tag': tag.tag,
 112         'field_type': tag.field_type,
 113         'field_offset': tag.field_offset,
 114         'field_length': tag.field_length,
 115         'values': None}
 116
 117     if isinstance(tag.printable, str):
 118         # Force it to be decoded as UTF-8 so that it'll fit into the DB
 119         data['printable'] = tag.printable.decode('utf8', 'replace')
 120
 121     if type(tag.values) == list:
 122         data['values'] = []
 123         for val in tag.values:
 124             if isinstance(val, Ratio):
 125                 data['values'].append(
 126                     _ratio_to_list(val))
 127             else:
 128                 data['values'].append(val)
 129     else:
 130         if isinstance(tag.values, str):
 131             # Force UTF-8, so that it fits into the DB
 132             data['values'] = tag.values.decode('utf8', 'replace')
 133         else:
 134             data['values'] = tag.values
 135
 136     return data
 137
 138
 139 def _ratio_to_list(ratio):
 140     return [ratio.num, ratio.den]
 141
 142
 143 def get_useful(tags):
 144     useful = {}
 145     for key, tag in tags.items():
 146         if key in USEFUL_TAGS:
 147             useful[key] = tag
 148
 149     return useful
 150
 151
 152 def get_gps_data(tags):
 153     """
 154     Processes EXIF data returned by EXIF.py
 155     """
 156     gps_data = {}
 157
 158     if not 'Image GPSInfo' in tags:
 159         return gps_data
 160
 161     try:
 162         dms_data = {
 163             'latitude': tags['GPS GPSLatitude'],
 164             'longitude': tags['GPS GPSLongitude']}
 165
 166         for key, dat in dms_data.items():
 167             gps_data[key] = (
 168                 lambda v:
 169                     float(v[0].num) / float(v[0].den) \
 170                     + (float(v[1].num) / float(v[1].den) / 60) \
 171                     + (float(v[2].num) / float(v[2].den) / (60 * 60))
 172                 )(dat.values)
 173
 174         if tags['GPS GPSLatitudeRef'].values == 'S':
 175             gps_data['latitude'] /= -1
 176
 177         if tags['GPS GPSLongitudeRef'].values == 'W':
 178             gps_data['longitude'] /= -1
 179
 180     except KeyError:
 181         pass
 182
 183     try:
 184         gps_data['direction'] = (
 185             lambda d:
 186                 float(d.num) / float(d.den)
 187             )(tags['GPS GPSImgDirection'].values[0])
 188     except KeyError:
 189         pass
 190
 191     try:
 192         gps_data['altitude'] = (
 193             lambda a:
 194                 float(a.num) / float(a.den)
 195             )(tags['GPS GPSAltitude'].values[0])
 196     except KeyError:
 197         pass
 198
 199     return gps_data