Allow writing of UNDEFINED tags

Tests/test_file_libtiff.py

@@ -299,13 +299,6 @@ class TestFileLibTiff(LibTiffTestCase):
                             )
                             continue
 
-                        if (
-                            libtiff
-                            and isinstance(value, bytes)
-                            and isinstance(tiffinfo, dict)
-                        ):
-                            value = value.decode()
-
                         assert reloaded_value == value
 
             # Test with types
@@ -682,6 +675,26 @@ class TestFileLibTiff(LibTiffTestCase):
         TiffImagePlugin.READ_LIBTIFF = False
         assert icc == icc_libtiff
 
+    def test_write_icc(self, tmp_path):
+        def check_write(libtiff):
+            TiffImagePlugin.WRITE_LIBTIFF = libtiff
+
+            with Image.open("Tests/images/hopper.iccprofile.tif") as img:
+                icc_profile = img.info["icc_profile"]
+
+                out = str(tmp_path / "temp.tif")
+                img.save(out, icc_profile=icc_profile)
+            with Image.open(out) as reloaded:
+                assert icc_profile == reloaded.info["icc_profile"]
+
+        libtiffs = []
+        if Image.core.libtiff_support_custom_tags:
+            libtiffs.append(True)
+        libtiffs.append(False)
+
+        for libtiff in libtiffs:
+            check_write(libtiff)
+
     def test_multipage_compression(self):
         with Image.open("Tests/images/compression.tif") as im:
 

src/PIL/TiffImagePlugin.py

@@ -553,9 +553,10 @@ class ImageFileDirectory_v2(MutableMapping):
                         )
                 elif all(isinstance(v, float) for v in values):
                     self.tagtype[tag] = TiffTags.DOUBLE
-                else:
+                elif all(isinstance(v, str) for v in values):
-                    if all(isinstance(v, str) for v in values):
+                    self.tagtype[tag] = TiffTags.ASCII
-                        self.tagtype[tag] = TiffTags.ASCII
+                elif all(isinstance(v, bytes) for v in values):
+                    self.tagtype[tag] = TiffTags.BYTE
 
         if self.tagtype[tag] == TiffTags.UNDEFINED:
             values = [
@@ -1548,16 +1549,17 @@ def _save(im, fp, filename):
             # Custom items are supported for int, float, unicode, string and byte
             # values. Other types and tuples require a tagtype.
             if tag not in TiffTags.LIBTIFF_CORE:
-                if (
+                if not Image.core.libtiff_support_custom_tags:
-                    TiffTags.lookup(tag).type == TiffTags.UNDEFINED
-                    or not Image.core.libtiff_support_custom_tags
-                ):
                     continue
 
                 if tag in ifd.tagtype:
                     types[tag] = ifd.tagtype[tag]
                 elif not (isinstance(value, (int, float, str, bytes))):
                     continue
+                else:
+                    type = TiffTags.lookup(tag).type
+                    if type:
+                        types[tag] = type
             if tag not in atts and tag not in blocklist:
                 if isinstance(value, str):
                     atts[tag] = value.encode("ascii", "replace") + b"\0"

src/encode.c

@@ -761,11 +761,6 @@ PyImaging_LibTiffEncoderNew(PyObject* self, PyObject* args)
             }
         }
 
-        if (PyBytes_Check(value) && type == TIFF_UNDEFINED) {
-            // For backwards compatibility
-            type = TIFF_ASCII;
-        }
-
         if (PyTuple_Check(value)) {
             Py_ssize_t len;
             len = PyTuple_Size(value);
@@ -797,7 +792,7 @@ PyImaging_LibTiffEncoderNew(PyObject* self, PyObject* args)
             }
         }
 
-        if (type == TIFF_BYTE) {
+        if (type == TIFF_BYTE || type == TIFF_UNDEFINED) {
             status = ImagingLibTiffSetField(&encoder->state,
                     (ttag_t) key_int,
                     PyBytes_Size(value), PyBytes_AsString(value));