MOBI Output: Add an option to not convert all images to JPEG when creating MOBI files

src/calibre/ebooks/conversion/plugins/mobi_output.py

@@ -56,7 +56,16 @@ class MOBIOutput(OutputFormatPlugin):
             help=_('Enable sharing of book content via Facebook etc. '
                 ' on the Kindle. WARNING: Using this feature means that '
                 ' the book will not auto sync its last read position '
-                ' on multiple devices. Complain to Amazon.'))
+                ' on multiple devices. Complain to Amazon.')
+        ),
+        OptionRecommendation(name='mobi_keep_original_images',
+            recommended_value=False,
+            help=_('By default calibre converts all images to JPEG format '
+                'in the output MOBI file. This is for maximum compatibility '
+                'as some older MOBI viewers have problems with other image '
+                'formats. This option tells calibre not to do this. '
+                'Useful if your document contains lots of GIF/PNG images that '
+                'become very large when converted to JPEG.')),
     ])
 
     def check_for_periodical(self):

src/calibre/ebooks/mobi/utils.py

@@ -7,7 +7,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2011, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
-import struct, string
+import struct, string, imghdr
 from collections import OrderedDict
 
 from calibre.utils.magick.draw import Image, save_cover_data_to, thumbnail
@@ -363,3 +363,11 @@ def to_base(num, base=32):
     ans.reverse()
     return ''.join(ans)
 
+def mobify_image(data):
+    'Convert PNG images to GIF as the idiotic Kindle cannot display some PNG'
+    what = imghdr.what(None, data)
+    if what == 'png':
+        data = save_cover_data_to(data, 'img.gif', return_data=True)
+    return data
+
+

src/calibre/ebooks/mobi/writer2/main.py

@@ -18,7 +18,7 @@ from calibre.ebooks.compression.palmdoc import compress_doc
 from calibre.ebooks.mobi.langcodes import iana2mobi
 from calibre.utils.filenames import ascii_filename
 from calibre.ebooks.mobi.writer2 import (PALMDOC, UNCOMPRESSED, RECORD_SIZE)
-from calibre.ebooks.mobi.utils import (rescale_image, encint,
+from calibre.ebooks.mobi.utils import (rescale_image, encint, mobify_image,
         encode_trailing_data, align_block, detect_periodical)
 from calibre.ebooks.mobi.writer2.indexer import Indexer
 from calibre.ebooks.mobi import MAX_THUMB_DIMEN, MAX_THUMB_SIZE
@@ -179,7 +179,11 @@ class MobiWriter(object):
         for item in self.oeb.manifest.values():
             if item.media_type not in OEB_RASTER_IMAGES: continue
             try:
-                data = rescale_image(item.data)
+                data = item.data
+                if self.opts.mobi_keep_original_images:
+                    data = mobify_image(data)
+                else:
+                    data = rescale_image(data)
             except:
                 oeb.logger.warn('Bad image file %r' % item.href)
                 continue

src/calibre/gui2/convert/mobi_output.py

@@ -22,6 +22,7 @@ class PluginWidget(Widget, Ui_Form):
     def __init__(self, parent, get_option, get_help, db=None, book_id=None):
         Widget.__init__(self, parent,
                 ['prefer_author_sort', 'toc_title',
+                    'mobi_keep_original_images',
                     'mobi_ignore_margins', 'mobi_toc_at_start',
                 'dont_compress', 'no_inline_toc', 'share_not_sync',
                 'personal_doc']#, 'mobi_navpoints_only_deepest']

src/calibre/gui2/convert/mobi_output.ui

@@ -14,7 +14,7 @@
    <string>Form</string>
   </property>
   <layout class="QGridLayout" name="gridLayout">
-   <item row="7" column="0" colspan="2">
+   <item row="8" column="0" colspan="2">
     <widget class="QGroupBox" name="groupBox">
      <property name="title">
       <string>Kindle options</string>
@@ -57,7 +57,7 @@
      </layout>
     </widget>
    </item>
-   <item row="8" column="0">
+   <item row="9" column="0">
     <spacer name="verticalSpacer_2">
      <property name="orientation">
       <enum>Qt::Vertical</enum>
@@ -104,7 +104,7 @@
    <item row="1" column="1">
     <widget class="QLineEdit" name="opt_toc_title"/>
    </item>
-   <item row="5" column="0">
+   <item row="6" column="0">
     <widget class="QCheckBox" name="opt_dont_compress">
      <property name="text">
       <string>Disable compression of the file contents</string>
@@ -118,6 +118,13 @@
      </property>
     </widget>
    </item>
+   <item row="5" column="0" colspan="2">
+    <widget class="QCheckBox" name="opt_mobi_keep_original_images">
+     <property name="text">
+      <string>Do not convert all images to &amp;JPEG (may result in images not working in older viewers)</string>
+     </property>
+    </widget>
+   </item>
   </layout>
  </widget>
  <resources/>