Edit book: Add a new image filter: Normalize -- to improve the contrast in images

src/calibre/gui2/tweak_book/editor/canvas.py

@@ -21,7 +21,7 @@ from calibre.gui2.dnd import (
     IMAGE_EXTENSIONS, dnd_has_extension, dnd_has_image, dnd_get_image, DownloadDialog)
 from calibre.gui2.tweak_book import capitalize
 from calibre.utils.imghdr import identify
-from calibre.utils.img import remove_borders, gaussian_sharpen, gaussian_blur, image_to_data, despeckle
+from calibre.utils.img import remove_borders, gaussian_sharpen, gaussian_blur, image_to_data, despeckle, normalize
 
 def painter(func):
     @wraps(func)
@@ -149,6 +149,13 @@ class Despeckle(Command):
     def __call__(self, canvas):
         return despeckle(canvas.current_image)
 
+class Normalize(Command):
+
+    TEXT = _('Normalize image')
+
+    def __call__(self, canvas):
+        return normalize(canvas.current_image)
+
 class Replace(Command):
 
     ''' Replace the current image with another image. If there is a selection,
@@ -368,6 +375,11 @@ class Canvas(QWidget):
         self.undo_stack.push(Despeckle(self))
         return True
 
+    @imageop
+    def normalize_image(self):
+        self.undo_stack.push(Normalize(self))
+        return True
+
     # The selection rectangle {{{
     @property
     def dc_size(self):

src/calibre/gui2/tweak_book/editor/image.py

@@ -273,6 +273,7 @@ class Editor(QMainWindow):
         m.addAction(_('Sharpen image'), self.sharpen_image)
         m.addAction(_('Blur image'), self.blur_image)
         m.addAction(_('De-speckle image'), self.canvas.despeckle_image)
+        m.addAction(_('Improve contrast (normalize image)'), self.canvas.normalize_image)
 
         self.info_bar = b = self.addToolBar(_('Image information bar'))
         b.setObjectName('image_info_bar')