gh-151888: Add tkinter PhotoImage.redither method

Wrap the photo image "redither" Tk command (since Tk 8.5) as the method
PhotoImage.redither(), which recalculates the dithered image in each
window where it is displayed (useful when the image data was supplied in
pieces), completing the wrapping of the photo image subcommands.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XWevzas4XVpjzedzR9gKVo

Author: serhiy-storchaka

Doc/library/tkinter.rst

@@ -5860,6 +5860,14 @@ Image classes
       it is displayed as transparent and the background of whatever window it
       is displayed in shows through.
 
+   .. method:: redither()
+
+      Recalculate the dithered image in each window where it is displayed.
+      This is useful when the image data was supplied in pieces, in which case
+      the dithered image may not be exactly correct.
+
+      .. versionadded:: next
+
    .. method:: cget(option)
 
       Return the current value of the configuration option *option*.

Doc/whatsnew/3.16.rst

@@ -157,6 +157,10 @@ tkinter
   synchronization of the displayed view with the underlying text.
   (Contributed by Serhiy Storchaka in :gh:`151675`.)
 
+* Added the :meth:`~tkinter.PhotoImage.redither` method which recalculates the
+  dithered image when its data was supplied in pieces.
+  (Contributed by Serhiy Storchaka in :gh:`151888`.)
+
 xml
 ---
 

Lib/test/test_tkinter/test_images.py

@@ -311,6 +311,12 @@ def test_blank(self):
         self.assertEqual(image.height(), 16)
         self.assertEqual(image.get(4, 6), self.colorlist(0, 0, 0))
 
+    def test_redither(self):
+        image = self.create()
+        pixel = image.get(4, 6)
+        image.redither()  # Recalculates the dithering; the data is unchanged.
+        self.assertEqual(image.get(4, 6), pixel)
+
     def test_copy(self):
         image = self.create()
         image2 = image.copy()

Lib/tkinter/__init__.py

@@ -4469,6 +4469,13 @@ def blank(self):
         """Display a transparent image."""
         self.tk.call(self.name, 'blank')
 
+    def redither(self):
+        """Recalculate the dithered image in each window where it is displayed.
+
+        Useful when the image data was supplied in pieces, in which case the
+        dithered image may not be exactly correct."""
+        self.tk.call(self.name, 'redither')
+
     def cget(self, option):
         """Return the value of OPTION."""
         return self.tk.call(self.name, 'cget', '-' + option)

Misc/NEWS.d/next/Library/2026-06-22-01-57-55.gh-issue-151888.hO7mxi.rst

@@ -0,0 +1,2 @@
+Add the :meth:`!tkinter.PhotoImage.redither` method, wrapping the photo image
+``redither`` Tk command.