Allow setting the cover for a book from one of the book's formats by right clicking on the format in the Book details panel. See #1515411 (Extract cover via book details and edit metadata)

src/calibre/gui2/actions/edit_metadata.py

@@ -7,6 +7,7 @@ __docformat__ = 'restructuredtext en'
 
 import os, shutil, copy
 from functools import partial
+from io import BytesIO
 
 from PyQt5.Qt import QMenu, QModelIndex, QTimer, QIcon, QApplication
 
@@ -785,3 +786,55 @@ class EditMetadataAction(InterfaceAction):
             affected_books = db.set_field(field, {book_id:''})
         if affected_books:
             self.refresh_books_after_metadata_edit(affected_books)
+
+    def set_cover_from_format(self, book_id, fmt):
+        from calibre.utils.config import prefs
+        from calibre.ebooks.metadata.meta import get_metadata
+        fmt = fmt.lower()
+        cdata = None
+        db = self.gui.current_db.new_api
+        if fmt == 'pdf':
+            pdfpath = db.format_abspath(book_id, fmt)
+            if pdfpath is None:
+                return error_dialog(self.gui, _('Format file missing'), _(
+                    'Cannot read cover as the %s file is missing from this book') % 'PDF', show=True)
+            from calibre.gui2.metadata.pdf_covers import PDFCovers
+            d = PDFCovers(pdfpath, parent=self.gui)
+            if d.exec_() == d.Accepted:
+                cpath = d.cover_path
+                if cpath:
+                    with open(cpath, 'rb') as f:
+                        cdata = f.read()
+            d.cleanup()
+        else:
+            stream = BytesIO()
+            try:
+                db.copy_format_to(book_id, fmt, stream)
+            except NoSuchFormat:
+                return error_dialog(self.gui, _('Format file missing'), _(
+                    'Cannot read cover as the %s file is missing from this book') % fmt.upper(), show=True)
+            old = prefs['read_file_metadata']
+            if not old:
+                prefs['read_file_metadata'] = True
+            try:
+                stream.seek(0)
+                mi = get_metadata(stream, fmt)
+            except Exception:
+                import traceback
+                return error_dialog(self.gui, _('Could not read metadata'),
+                            _('Could not read metadata from %s format')%fmt.upper(),
+                             det_msg=traceback.format_exc(), show=True)
+            finally:
+                if old != prefs['read_file_metadata']:
+                    prefs['read_file_metadata'] = old
+            if mi.cover and os.access(mi.cover, os.R_OK):
+                cdata = open(mi.cover).read()
+            elif mi.cover_data[1] is not None:
+                cdata = mi.cover_data[1]
+            if cdata is None:
+                return error_dialog(self.gui, _('Could not read cover'),
+                            _('Could not read cover from %s format')%fmt.upper(), show=True)
+        db.set_cover({book_id:cdata})
+        current_idx = self.gui.library_view.currentIndex()
+        self.gui.library_view.model().current_changed(current_idx, current_idx)
+        self.gui.refresh_cover_browser()

src/calibre/gui2/book_details.py

@@ -130,10 +130,12 @@ def details_context_menu_event(view, ev, book_info):  # {{{
                 ofmt = fmt.upper() if fmt.startswith('ORIGINAL_') else 'ORIGINAL_' + fmt
                 nfmt = ofmt[len('ORIGINAL_'):]
                 fmts = {x.upper() for x in db.formats(book_id)}
-                for a, t in [('remove', _('Delete the %s format')),
+                for a, t in [
-                    ('save', _('Save the %s format to disk')),
+                        ('remove', _('Delete the %s format')),
-                    ('restore', _('Restore the %s format')),
+                        ('save', _('Save the %s format to disk')),
-                    ('compare', ''),
+                        ('restore', _('Restore the %s format')),
+                        ('compare', ''),
+                        ('set_cover', _('Set the book cover from the %s file')),
                 ]:
                     if a == 'restore' and not fmt.startswith('ORIGINAL_'):
                         continue
@@ -401,6 +403,7 @@ class BookInfo(QWebView):
     save_format = pyqtSignal(int, object)
     restore_format = pyqtSignal(int, object)
     compare_format = pyqtSignal(int, object)
+    set_cover_format = pyqtSignal(int, object)
     copy_link = pyqtSignal(object)
     manage_author = pyqtSignal(object)
     open_fmt_with = pyqtSignal(int, object, object)
@@ -422,7 +425,9 @@ class BookInfo(QWebView):
         for x, icon in [
             ('remove_format', 'trash.png'), ('save_format', 'save.png'),
             ('restore_format', 'edit-undo.png'), ('copy_link','edit-copy.png'),
-            ('manage_author', 'user_profile.png'), ('compare_format', 'diff.png')]:
+            ('manage_author', 'user_profile.png'), ('compare_format', 'diff.png'),
+            ('set_cover_format', 'book.png'),
+        ]:
             ac = QAction(QIcon(I(icon)), '', self)
             ac.current_fmt = None
             ac.current_url = None
@@ -459,6 +464,9 @@ class BookInfo(QWebView):
     def compare_format_triggerred(self):
         self.context_action_triggered('compare_format')
 
+    def set_cover_format_triggerred(self):
+        self.context_action_triggered('set_cover_format')
+
     def copy_link_triggerred(self):
         self.context_action_triggered('copy_link')
 
@@ -603,6 +611,7 @@ class BookDetails(QWidget):  # {{{
     remove_metadata_item = pyqtSignal(int, object, object)
     save_specific_format = pyqtSignal(int, object)
     restore_specific_format = pyqtSignal(int, object)
+    set_cover_from_format = pyqtSignal(int, object)
     compare_specific_format = pyqtSignal(int, object)
     copy_link = pyqtSignal(object)
     remote_file_dropped = pyqtSignal(object, object)
@@ -680,6 +689,7 @@ class BookDetails(QWidget):  # {{{
         self.book_info.open_fmt_with.connect(self.open_fmt_with)
         self.book_info.save_format.connect(self.save_specific_format)
         self.book_info.restore_format.connect(self.restore_specific_format)
+        self.book_info.set_cover_format.connect(self.set_cover_from_format)
         self.book_info.compare_format.connect(self.compare_specific_format)
         self.book_info.copy_link.connect(self.copy_link)
         self.book_info.manage_author.connect(self.manage_author)

src/calibre/gui2/init.py

@@ -528,6 +528,8 @@ class LayoutMixin(object):  # {{{
                 self.iactions['Save To Disk'].save_library_format_by_ids)
         self.book_details.restore_specific_format.connect(
             self.iactions['Remove Books'].restore_format)
+        self.book_details.set_cover_from_format.connect(
+            self.iactions['Edit Metadata'].set_cover_from_format)
         self.book_details.copy_link.connect(self.bd_copy_link,
                 type=Qt.QueuedConnection)
         self.book_details.view_device_book.connect(