Added alpha_only argument to getbbox()

Tests/test_file_apng.py

@@ -374,6 +374,20 @@ def test_apng_save(tmp_path):
         assert im.getpixel((64, 32)) == (0, 255, 0, 255)
 
 
+def test_apng_save_alpha(tmp_path):
+    test_file = str(tmp_path / "temp.png")
+
+    im = Image.new("RGBA", (1, 1), (255, 0, 0, 255))
+    im2 = Image.new("RGBA", (1, 1), (255, 0, 0, 127))
+    im.save(test_file, save_all=True, append_images=[im2])
+
+    with Image.open(test_file) as reloaded:
+        assert reloaded.getpixel((0, 0)) == (255, 0, 0, 255)
+
+        reloaded.seek(1)
+        assert reloaded.getpixel((0, 0)) == (255, 0, 0, 127)
+
+
 def test_apng_save_split_fdat(tmp_path):
     # test to make sure we do not generate sequence errors when writing
     # frames with image data spanning multiple fdAT chunks (in this case

Tests/test_file_gif.py

@@ -1130,6 +1130,18 @@ def test_bbox(tmp_path):
         assert reread.n_frames == 2
 
 
+def test_bbox_alpha(tmp_path):
+    out = str(tmp_path / "temp.gif")
+
+    im = Image.new("RGBA", (1, 2), (255, 0, 0, 255))
+    im.putpixel((0, 1), (255, 0, 0, 0))
+    im2 = Image.new("RGBA", (1, 2), (255, 0, 0, 0))
+    im.save(out, save_all=True, append_images=[im2])
+
+    with Image.open(out) as reread:
+        assert reread.n_frames == 2
+
+
 def test_palette_save_L(tmp_path):
     # Generate an L mode image with a separate palette
 

Tests/test_image_getbbox.py

@@ -1,3 +1,5 @@
+import pytest
+
 from PIL import Image
 
 from .helper import hopper
@@ -38,3 +40,16 @@ def check(im, fill_color):
         for color in ((0, 0), (127, 0), (255, 0)):
             im = Image.new(mode, (100, 100), color)
             check(im, (255, 255))
+
+
+@pytest.mark.parametrize("mode", ("RGBA", "RGBa", "La", "LA", "PA"))
+def test_bbox_alpha_only_false(mode):
+    im = Image.new(mode, (100, 100))
+    assert im.getbbox(alpha_only=False) is None
+
+    fill_color = [1] * Image.getmodebands(mode)
+    fill_color[-1] = 0
+    im.paste(tuple(fill_color), (25, 25, 75, 75))
+    assert im.getbbox(alpha_only=False) == (25, 25, 75, 75)
+
+    assert im.getbbox() is None

src/PIL/GifImagePlugin.py

@@ -569,9 +569,9 @@ def _getbbox(base_im, im_frame):
         delta = ImageChops.subtract_modulo(im_frame, base_im)
     else:
         delta = ImageChops.subtract_modulo(
-            im_frame.convert("RGB"), base_im.convert("RGB")
+            im_frame.convert("RGBA"), base_im.convert("RGBA")
         )
-    return delta.getbbox()
+    return delta.getbbox(alpha_only=False)
 
 
 def _write_multiple_frames(im, fp, palette):

src/PIL/Image.py

@@ -1293,11 +1293,15 @@ def getbands(self):
         """
         return ImageMode.getmode(self.mode).bands
 
-    def getbbox(self):
+    def getbbox(self, *, alpha_only=True):
         """
         Calculates the bounding box of the non-zero regions in the
         image.
 
+        :param alpha_only: Optional flag, defaulting to ``True``.
+           If ``True`` and the image has an alpha channel, trim transparent pixels.
+           Otherwise, trim pixels when all channels are zero.
+           Keyword-only argument.
         :returns: The bounding box is returned as a 4-tuple defining the
            left, upper, right, and lower pixel coordinate. See
            :ref:`coordinate-system`. If the image is completely empty, this
@@ -1306,7 +1310,7 @@ def getbbox(self):
         """
 
         self.load()
-        return self.im.getbbox()
+        return self.im.getbbox(alpha_only)
 
     def getcolors(self, maxcolors=256):
         """

src/PIL/PngImagePlugin.py

@@ -1138,9 +1138,9 @@ def _write_multiple_frames(im, fp, chunk, rawmode, default_image, append_images)
                 else:
                     base_im = previous["im"]
                 delta = ImageChops.subtract_modulo(
-                    im_frame.convert("RGB"), base_im.convert("RGB")
+                    im_frame.convert("RGBA"), base_im.convert("RGBA")
                 )
-                bbox = delta.getbbox()
+                bbox = delta.getbbox(alpha_only=False)
                 if (
                     not bbox
                     and prev_disposal == encoderinfo.get("disposal")

src/_imaging.c

@@ -2159,9 +2159,15 @@ _isblock(ImagingObject *self) {
 }
 
 static PyObject *
-_getbbox(ImagingObject *self) {
+_getbbox(ImagingObject *self, PyObject *args) {
     int bbox[4];
-    if (!ImagingGetBBox(self->image, bbox)) {
+
+    int alpha_only = 1;
+    if (!PyArg_ParseTuple(args, "|i", &alpha_only)) {
+        return NULL;
+    }
+
+    if (!ImagingGetBBox(self->image, bbox, alpha_only)) {
         Py_INCREF(Py_None);
         return Py_None;
     }
@@ -3573,7 +3579,7 @@ static struct PyMethodDef methods[] = {
 
     {"isblock", (PyCFunction)_isblock, METH_NOARGS},
 
-    {"getbbox", (PyCFunction)_getbbox, METH_NOARGS},
+    {"getbbox", (PyCFunction)_getbbox, METH_VARARGS},
     {"getcolors", (PyCFunction)_getcolors, METH_VARARGS},
     {"getextrema", (PyCFunction)_getextrema, METH_NOARGS},
     {"getprojection", (PyCFunction)_getprojection, METH_NOARGS},

src/libImaging/GetBBox.c

@@ -19,7 +19,7 @@
 #include "Imaging.h"
 
 int
-ImagingGetBBox(Imaging im, int bbox[4]) {
+ImagingGetBBox(Imaging im, int bbox[4], int alpha_only) {
     /* Get the bounding box for any non-zero data in the image.*/
 
     int x, y;
@@ -58,10 +58,11 @@ ImagingGetBBox(Imaging im, int bbox[4]) {
         INT32 mask = 0xffffffff;
         if (im->bands == 3) {
             ((UINT8 *)&mask)[3] = 0;
-        } else if (
+        } else if (alpha_only && (
             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) {
+            strcmp(im->mode, "PA") == 0
+        )) {
 #ifdef WORDS_BIGENDIAN
             mask = 0x000000ff;
 #else

src/libImaging/Imaging.h

@@ -317,7 +317,7 @@ ImagingMerge(const char *mode, Imaging bands[4]);
 extern int
 ImagingSplit(Imaging im, Imaging bands[4]);
 extern int
-ImagingGetBBox(Imaging im, int bbox[4]);
+ImagingGetBBox(Imaging im, int bbox[4], int alpha_only);
 typedef struct {
     int x, y;
     INT32 count;