From 0aea24227a4bf37a63bedfbbea7a8fbe4003d98a Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Sat, 12 Aug 2023 16:46:47 +1000
Subject: [PATCH] Improve efficiency when a radius is zero

---
 src/PIL/ImageFilter.py   |  4 ++++
 src/libImaging/BoxBlur.c | 42 ++++++++++++++++++++++++----------------
 2 files changed, 29 insertions(+), 17 deletions(-)

diff --git a/src/PIL/ImageFilter.py b/src/PIL/ImageFilter.py
index 0d2fec9ee78..57268b8f53d 100644
--- a/src/PIL/ImageFilter.py
+++ b/src/PIL/ImageFilter.py
@@ -170,6 +170,8 @@ def filter(self, image):
         xy = self.radius
         if not isinstance(xy, (tuple, list)):
             xy = (xy, xy)
+        if xy == (0, 0):
+            return image.copy()
         return image.gaussian_blur(xy)
 
 
@@ -202,6 +204,8 @@ def filter(self, image):
         xy = self.radius
         if not isinstance(xy, (tuple, list)):
             xy = (xy, xy)
+        if xy == (0, 0):
+            return image.copy()
         return image.box_blur(xy)
 
 
diff --git a/src/libImaging/BoxBlur.c b/src/libImaging/BoxBlur.c
index 41e9fbed9cb..a4006dd0a20 100644
--- a/src/libImaging/BoxBlur.c
+++ b/src/libImaging/BoxBlur.c
@@ -258,29 +258,37 @@ ImagingBoxBlur(Imaging imOut, Imaging imIn, float xradius, float yradius, int n)
         return ImagingError_ModeError();
     }
 
-    imTransposed = ImagingNewDirty(imIn->mode, imIn->ysize, imIn->xsize);
-    if (!imTransposed) {
-        return NULL;
-    }
-
     /* Apply blur in one dimension.
        Use imOut as a destination at first pass,
        then use imOut as a source too. */
-    ImagingHorizontalBoxBlur(imOut, imIn, xradius);
-    for (i = 1; i < n; i++) {
-        ImagingHorizontalBoxBlur(imOut, imOut, xradius);
-    }
-    /* Transpose result for blur in another direction. */
-    ImagingTranspose(imTransposed, imOut);
 
-    /* Reuse imTransposed as a source and destination there. */
-    for (i = 0; i < n; i++) {
-        ImagingHorizontalBoxBlur(imTransposed, imTransposed, yradius);
+    if (xradius != 0) {
+        ImagingHorizontalBoxBlur(imOut, imIn, xradius);
+        for (i = 1; i < n; i++) {
+            ImagingHorizontalBoxBlur(imOut, imOut, xradius);
+        }
     }
-    /* Restore original orientation. */
-    ImagingTranspose(imOut, imTransposed);
+    if (yradius != 0) {
+        imTransposed = ImagingNewDirty(imIn->mode, imIn->ysize, imIn->xsize);
+        if (!imTransposed) {
+            return NULL;
+        }
 
-    ImagingDelete(imTransposed);
+        /* Transpose result for blur in another direction. */
+        ImagingTranspose(imTransposed, xradius == 0 ? imIn : imOut);
+
+        /* Reuse imTransposed as a source and destination there. */
+        for (i = 0; i < n; i++) {
+            ImagingHorizontalBoxBlur(imTransposed, imTransposed, yradius);
+        }
+        /* Restore original orientation. */
+        ImagingTranspose(imOut, imTransposed);
+
+        ImagingDelete(imTransposed);
+    }
+    if (xradius == 0 && yradius == 0) {
+        ImagingCopy2(imOut, imIn);
+    }
 
     return imOut;
 }