diff --git a/src/calibre/devices/kobo/driver.py b/src/calibre/devices/kobo/driver.py
index 19aac74d4b..99eab9c433 100644
--- a/src/calibre/devices/kobo/driver.py
+++ b/src/calibre/devices/kobo/driver.py
@@ -1023,7 +1023,7 @@ class KOBO(USBMS):
             debug_print('FAILED to upload cover', filepath)
 
     def _upload_cover(self, path, filename, metadata, filepath, uploadgrayscale, ditheredcovers, letterboxcovers, pngcovers):
-        from calibre.utils.img import save_cover_data_to
+        from calibre.utils.img import save_cover_data_to, optimize_png
         if metadata.cover:
             cover = self.normalize_path(metadata.cover.replace('/', os.sep))
 
@@ -1077,6 +1077,9 @@ class KOBO(USBMS):
                                 f.write(data)
                                 fsync(f)
 
+                            if pngcovers:
+                                optimize_png(fpath)
+
                 else:
                     debug_print("ImageID could not be retreived from the database")
 
@@ -2697,6 +2700,7 @@ class KOBOTOUCH(KOBO):
 
     def _upload_cover(self, path, filename, metadata, filepath, upload_grayscale, dithered_covers=False, keep_cover_aspect=False, letterbox_fs_covers=False, png_covers=False):
         from calibre.utils.imghdr import identify
+        from calibre.utils.img import optimize_png
         debug_print("KoboTouch:_upload_cover - filename='%s' upload_grayscale='%s' dithered_covers='%s' "%(filename, upload_grayscale, dithered_covers))
 
         if not metadata.cover:
@@ -2780,6 +2784,9 @@ class KOBOTOUCH(KOBO):
                         with lopen(fpath, 'wb') as f:
                             f.write(data)
                             fsync(f)
+
+                        if png_covers:
+                            optimize_png(fpath)
         except Exception as e:
             err = unicode_type(e)
             debug_print("KoboTouch:_upload_cover - Exception string: %s"%err)
diff --git a/src/calibre/utils/imageops/ordered_dither.cpp b/src/calibre/utils/imageops/ordered_dither.cpp
index bf85727b0c..3d766a059b 100644
--- a/src/calibre/utils/imageops/ordered_dither.cpp
+++ b/src/calibre/utils/imageops/ordered_dither.cpp
@@ -79,6 +79,7 @@ QImage ordered_dither(const QImage &image) { // {{{
     QImage img = image;
     int y = 0, x = 0, width = img.width(), height = img.height();
     uint8_t gray = 0, dithered = 0;
+    // NOTE: We went with Grayscale8 because QImageWriter was doing some weird things with an Indexed8 input...
     QImage dst(width, height, QImage::Format_Grayscale8);
 
     // We're running behind blend_image, so, we should only ever be fed RGB32 as input...
diff --git a/src/calibre/utils/img.py b/src/calibre/utils/img.py
index f333755d54..097ce0ca37 100644
--- a/src/calibre/utils/img.py
+++ b/src/calibre/utils/img.py
@@ -233,7 +233,7 @@ def save_cover_data_to(data, path=None, bgcolor='#ffffff', resize_to=None, compr
             img = grayscale_image(img)
     if eink:
         # NOTE: Keep in mind that JPG does NOT actually support indexed colors, so the JPG algorithm will then smush everything back into a 256c mess...
-        #       Thankfully, Nickel handles PNG just fine, and we generate smaller files to boot, because they're properly color indexed ;).
+        #       Thankfully, Nickel handles PNG just fine, and we potentially generate smaller files to boot, because they can be properly color indexed ;).
         img = eink_dither_image(img)
         changed = True
     if path is None: