Ignore unspecified extra samples for TIFF separate planar configuration (#9514)

Tests/test_file_libtiff.py

@@ -1055,6 +1055,15 @@ class TestFileLibTiff(LibTiffTestCase):
         with Image.open("Tests/images/tiff_strip_planar_16bit_RGBa.tiff") as im:
             assert_image_equal_tofile(im, "Tests/images/tiff_16bit_RGBa_target.png")
 
+    def test_separate_planar_extra_samples(self, tmp_path: Path) -> None:
+        out = tmp_path / "temp.tif"
+        with Image.open("Tests/images/separate_planar_extra_samples.tiff") as im:
+            assert im.mode == "L"
+
+            im.save(out)
+        with Image.open(out) as reloaded:
+            assert reloaded.mode == "L"
+
     @pytest.mark.parametrize("compression", (None, "jpeg"))
     def test_block_tile_tags(self, compression: str | None, tmp_path: Path) -> None:
         im = hopper()

src/PIL/TiffImagePlugin.py

@@ -1473,28 +1473,34 @@ class TiffImageFile(ImageFile.ImageFile):
         logger.debug("- size: %s", self.size)
 
         sample_format = self.tag_v2.get(SAMPLEFORMAT, (1,))
-        if len(sample_format) > 1 and max(sample_format) == min(sample_format) == 1:
+        if len(sample_format) > 1 and max(sample_format) == min(sample_format):
             # SAMPLEFORMAT is properly per band, so an RGB image will
             # be (1,1,1).  But, we don't support per band pixel types,
             # and anything more than one band is a uint8. So, just
             # take the first element. Revisit this if adding support
             # for more exotic images.
-            sample_format = (1,)
+            sample_format = (sample_format[0],)
 
         bps_tuple = self.tag_v2.get(BITSPERSAMPLE, (1,))
         extra_tuple = self.tag_v2.get(EXTRASAMPLES, ())
+        samples_per_pixel = self.tag_v2.get(
+            SAMPLESPERPIXEL,
+            3 if self._compression == "tiff_jpeg" and photo in (2, 6) else 1,
+        )
         if photo in (2, 6, 8):  # RGB, YCbCr, LAB
             bps_count = 3
         elif photo == 5:  # CMYK
             bps_count = 4
         else:
             bps_count = 1
+        if self._planar_configuration == 2 and extra_tuple and max(extra_tuple) == 0:
+            # If components are stored separately,
+            # then unspecified extra components at the end can be ignored
+            bps_tuple = bps_tuple[: -len(extra_tuple)]
+            samples_per_pixel -= len(extra_tuple)
+            extra_tuple = ()
         bps_count += len(extra_tuple)
         bps_actual_count = len(bps_tuple)
-        samples_per_pixel = self.tag_v2.get(
-            SAMPLESPERPIXEL,
-            3 if self._compression == "tiff_jpeg" and photo in (2, 6) else 1,
-        )
 
         if samples_per_pixel > MAX_SAMPLESPERPIXEL:
             # DOS check, samples_per_pixel can be a Long, and we extend the tuple below
@@ -1762,6 +1768,12 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
         legacy_ifd = im.tag.to_v2()
 
     supplied_tags = {**legacy_ifd, **getattr(im, "tag_v2", {})}
+    if supplied_tags.get(PLANAR_CONFIGURATION) == 2 and EXTRASAMPLES in supplied_tags:
+        # If the image used separate component planes,
+        # then EXTRASAMPLES should be ignored when saving contiguously
+        if SAMPLESPERPIXEL in supplied_tags:
+            supplied_tags[SAMPLESPERPIXEL] -= len(supplied_tags[EXTRASAMPLES])
+        del supplied_tags[EXTRASAMPLES]
     for tag in (
         # IFD offset that may not be correct in the saved image
         EXIFIFD,