When setting covers in calibre, resize to fit within a maximum size of (1200, 1600), to prevent slowdowns due to extra large covers. This size can be controlled via Preferences->Tweaks. Fixes #9277 (Restrict max cover size to 1000x1000)

resources/default_tweaks.py

@@ -349,3 +349,9 @@ public_smtp_relay_delay = 301
 # after a restart of calibre.
 draw_hidden_section_indicators = True
 
+#: The maximum width and height for covers saved in the calibre library
+# All covers in the calibre library will be resized, preserving aspect ratio,
+# to fit within this size. This is to prevent slowdowns caused by extremely
+# large covers
+maximum_cover_size = (1200, 1600)
+

src/calibre/library/database2.py

@@ -37,7 +37,7 @@ from calibre.utils.config import prefs, tweaks, from_json, to_json
 from calibre.utils.icu import sort_key
 from calibre.utils.search_query_parser import saved_searches, set_saved_searches
 from calibre.ebooks import BOOK_EXTENSIONS, check_ebook_format
-from calibre.utils.magick.draw import save_cover_data_to
+from calibre.utils.magick.draw import minify_image, save_cover_data_to
 from calibre.utils.recycle_bin import delete_file, delete_tree
 from calibre.utils.formatter_functions import load_user_template_functions
 
@@ -951,6 +951,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
             if callable(getattr(data, 'read', None)):
                 data = data.read()
             try:
+                data = minify_image(data, tweaks['maximum_cover_size'])
                 save_cover_data_to(data, path)
             except (IOError, OSError):
                 time.sleep(0.2)

src/calibre/utils/magick/draw.py

@@ -12,6 +12,34 @@ from calibre.constants import __appname__, __version__
 from calibre.utils.config import tweaks
 from calibre import fit_image
 
+def _data_to_image(data):
+    if isinstance(data, Image):
+        img = data
+    else:
+        img = Image()
+        img.load(data)
+    return img
+
+def minify_image(data, minify_to=(1200, 1600), preserve_aspect_ratio=True):
+    '''
+    Minify image to specified size if image is bigger than specified
+    size and return minified image, otherwise, original image is
+    returned.
+
+    :param data: Image data as bytestring or Image object
+    :param minify_to: A tuple (width, height) to specify target size
+    :param preserve_aspect_ratio: whether preserve original aspect ratio
+    '''
+    img = _data_to_image(data)
+    owidth, oheight = img.size
+    nwidth, nheight = minify_to
+    if owidth <= nwidth and oheight <= nheight:
+        return img
+    if preserve_aspect_ratio:
+        scaled, nwidth, nheight = fit_image(owidth, oheight, nwidth, nheight)
+    img.size = (nwidth, nheight)
+    return img
+
 def normalize_format_name(fmt):
     fmt = fmt.lower()
     if fmt == 'jpeg':
@@ -35,11 +63,7 @@ def save_cover_data_to(data, path, bgcolor='#ffffff', resize_to=None,
 
     '''
     changed = False
-    if isinstance(data, Image):
+    img = _data_to_image(data)
-        img = data
-    else:
-        img = Image()
-        img.load(data)
     orig_fmt = normalize_format_name(img.format)
     fmt = os.path.splitext(path)[1]
     fmt = normalize_format_name(fmt[1:])