Allow libtiff to write COLORMAP tag

Tests/test_file_libtiff.py

@@ -203,6 +203,7 @@ class TestFileLibTiff(LibTiffTestCase):
                     del core_items[tag]
                 except KeyError:
                     pass
+            del core_items[320]  # colormap is special, tested below
 
             # Type codes:
             #     2: "ascii",
@@ -479,6 +480,18 @@ class TestFileLibTiff(LibTiffTestCase):
         with Image.open(out) as im2:
             assert_image_equal(im, im2)
 
+    def test_palette_save(self, tmp_path):
+        im = hopper("P")
+        out = str(tmp_path / "temp.tif")
+
+        TiffImagePlugin.WRITE_LIBTIFF = True
+        im.save(out)
+        TiffImagePlugin.WRITE_LIBTIFF = False
+
+        with Image.open(out) as reloaded:
+            # colormap/palette tag
+            assert len(reloaded.tag_v2[320]) == 768
+
     def xtest_bw_compression_w_rgb(self, tmp_path):
         """ This test passes, but when running all tests causes a failure due
             to output on stderr from the error thrown by libtiff. We need to

src/PIL/TiffImagePlugin.py

@@ -1524,7 +1524,6 @@ def _save(im, fp, filename):
         # BITSPERSAMPLE, etc), passing arrays with a different length will result in
         # segfaults. Block these tags until we add extra validation.
         blocklist = [
-            COLORMAP,
             REFERENCEBLACKWHITE,
             SAMPLEFORMAT,
             STRIPBYTECOUNTS,

src/PIL/TiffTags.py

@@ -483,7 +483,6 @@ LIBTIFF_CORE = {
     65537,
 }
 
-LIBTIFF_CORE.remove(320)  # Array of short, crashes
 LIBTIFF_CORE.remove(301)  # Array of short, crashes
 LIBTIFF_CORE.remove(532)  # Array of long, crashes
 

src/encode.c

@@ -671,7 +671,7 @@ PyImaging_LibTiffEncoderNew(PyObject* self, PyObject* args)
     // This list also exists in TiffTags.py
     const int core_tags[] = {
         256, 257, 258, 259, 262, 263, 266, 269, 274, 277, 278, 280, 281, 340,
-        341, 282, 283, 284, 286, 287, 296, 297, 321, 338, 32995, 32998, 32996,
+        341, 282, 283, 284, 286, 287, 296, 297, 320, 321, 338, 32995, 32998, 32996,
         339, 32997, 330, 531, 530, 65537
     };
 
@@ -801,7 +801,26 @@ PyImaging_LibTiffEncoderNew(PyObject* self, PyObject* args)
             TRACE(("Setting from Tuple: %d \n", key_int));
             len = PyTuple_Size(value);
 
-            if (type == TIFF_SHORT) {
+            if (key_int == TIFFTAG_COLORMAP) {
+                int stride = 256;
+                if (len != 768) {
+                    PyErr_SetString(PyExc_ValueError, "Requiring 768 items for for Colormap");
+                    return NULL;
+                }
+                UINT16 *av;
+                /* malloc check ok, calloc checks for overflow */
+                av = calloc(len, sizeof(UINT16));
+                if (av) {
+                    for (i=0;i<len;i++) {
+                        av[i] = (UINT16)PyLong_AsLong(PyTuple_GetItem(value,i));
+                    }
+                    status = ImagingLibTiffSetField(&encoder->state, (ttag_t) key_int,
+                                                    av,
+                                                    av + stride,
+                                                    av + stride * 2);
+                    free(av);
+                }
+            } else if (type == TIFF_SHORT) {
                 UINT16 *av;
                 /* malloc check ok, calloc checks for overflow */
                 av = calloc(len, sizeof(UINT16));