If present, only use alpha channel for bounding box

Tests/test_image_getbbox.py

@@ -10,29 +10,32 @@ def test_sanity():
 
 
 def test_bbox():
+    def check(im, fill_color):
+        assert im.getbbox() is None
 
-    # 8-bit mode
-    im = Image.new("L", (100, 100), 0)
-    assert im.getbbox() is None
+        im.paste(fill_color, (10, 25, 90, 75))
+        assert im.getbbox() == (10, 25, 90, 75)
 
-    im.paste(255, (10, 25, 90, 75))
-    assert im.getbbox() == (10, 25, 90, 75)
+        im.paste(fill_color, (25, 10, 75, 90))
+        assert im.getbbox() == (10, 10, 90, 90)
 
-    im.paste(255, (25, 10, 75, 90))
-    assert im.getbbox() == (10, 10, 90, 90)
+        im.paste(fill_color, (-10, -10, 110, 110))
+        assert im.getbbox() == (0, 0, 100, 100)
 
-    im.paste(255, (-10, -10, 110, 110))
-    assert im.getbbox() == (0, 0, 100, 100)
+    # 8-bit mode
+    im = Image.new("L", (100, 100), 0)
+    check(im, 255)
 
     # 32-bit mode
     im = Image.new("RGB", (100, 100), 0)
-    assert im.getbbox() is None
-
-    im.paste(255, (10, 25, 90, 75))
-    assert im.getbbox() == (10, 25, 90, 75)
+    check(im, 255)
 
-    im.paste(255, (25, 10, 75, 90))
-    assert im.getbbox() == (10, 10, 90, 90)
+    for mode in ("RGBA", "RGBa"):
+        for color in ((0, 0, 0, 0), (127, 127, 127, 0), (255, 255, 255, 0)):
+            im = Image.new(mode, (100, 100), color)
+            check(im, (255, 255, 255, 255))
 
-    im.paste(255, (-10, -10, 110, 110))
-    assert im.getbbox() == (0, 0, 100, 100)
+    for mode in ("La", "LA", "PA"):
+        for color in ((0, 0), (127, 0), (255, 0)):
+            im = Image.new(mode, (100, 100), color)
+            check(im, (255, 255))

docs/releasenotes/7.1.0.rst

@@ -1,6 +1,9 @@
 7.0.0
 -----
 
+API Changes
+===========
+
 Allow saving of zero quality JPEG images
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -14,3 +17,15 @@ been resolved.
     from PIL import Image
     im = Image.open("hopper.jpg")
     im.save("out.jpg", quality=0)
+
+Other Changes
+=============
+
+If present, only use alpha channel for bounding box
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When the :py:meth:`~PIL.Image.Image.getbbox` method calculates the bounding
+box, for an RGB image it trims black pixels. Similarly, for an RGBA image it
+would trim black transparent pixels. This is now changed so that if an image
+has an alpha channel (RGBA, RGBa, PA, LA, La), any transparent pixels are
+trimmed.

src/libImaging/GetBBox.c

@@ -55,8 +55,19 @@ ImagingGetBBox(Imaging im, int bbox[4])
 	GETBBOX(image8, 0xff);
     } else {
 	INT32 mask = 0xffffffff;
-	if (im->bands == 3)
+	if (im->bands == 3) {
 	    ((UINT8*) &mask)[3] = 0;
+	} else if (strcmp(im->mode, "RGBa") == 0 ||
+	           strcmp(im->mode, "RGBA") == 0 ||
+	           strcmp(im->mode, "La") == 0 ||
+	           strcmp(im->mode, "LA") == 0 ||
+	           strcmp(im->mode, "PA") == 0) {
+#ifdef WORDS_BIGENDIAN
+	    mask = 0x000000ff;
+#else
+	    mask = 0xff000000;
+#endif
+	}
 	GETBBOX(image32, mask);
     }