Ignore padding bytes in getcolors() for two band images

Tests/test_image_getcolors.py

@@ -1,5 +1,9 @@
 from __future__ import annotations
 
+import pytest
+
+from PIL import Image
+
 from .helper import hopper
 
 
@@ -16,9 +20,12 @@ def getcolors(mode: str, limit: int | None = None) -> int | None:
 
     assert getcolors("1") == 2
     assert getcolors("L") == 255
+    assert getcolors("LA") == 255
+    assert getcolors("La") == 255
     assert getcolors("I") == 255
     assert getcolors("F") == 255
     assert getcolors("P") == 96  # fixed palette
+    assert getcolors("PA") == 96
     assert getcolors("RGB") is None
     assert getcolors("RGBA") is None
     assert getcolors("CMYK") is None
@@ -36,6 +43,17 @@ def getcolors(mode: str, limit: int | None = None) -> int | None:
     assert getcolors("YCbCr", 16384) == 9329
 
 
+@pytest.mark.parametrize("mode", ("LA", "La", "PA"))
+def test_two_bands(mode: str) -> None:
+    im = Image.new(mode, (2, 1), (1, 2))
+
+    bands = [Image.new("L", (1, 1), color) for color in (1, 2)]
+    im_merged = Image.merge(mode, bands)
+
+    im.paste(im_merged)
+    assert im.getcolors() == [(2, (1, 2))]
+
+
 def test_negative_maxcolors() -> None:
     im = hopper()
     assert im.getcolors(-1) is None

src/libImaging/GetBBox.c

@@ -388,7 +388,10 @@ getcolors32(Imaging im, int maxcolors, int *size) {
     }
 
     pixel_mask = 0xffffffff;
-    if (im->bands == 3) {
+    if (im->bands == 2) {
+        ((UINT8 *)&pixel_mask)[1] = 0;
+        ((UINT8 *)&pixel_mask)[2] = 0;
+    } else if (im->bands == 3) {
         ((UINT8 *)&pixel_mask)[3] = 0;
     }