Support writing SIGNED_RATIONAL tag types

Author: radarhere

Tests/test_file_libtiff.py

@@ -355,6 +355,22 @@ def test_subifd(self, tmp_path: Path) -> None:
             # Should not segfault
             im.save(outfile)
 
+    def test_signed_rational(
+        self, monkeypatch: pytest.MonkeyPatch, tmp_path: Path
+    ) -> None:
+        monkeypatch.setattr(TiffImagePlugin, "WRITE_LIBTIFF", True)
+
+        ifd = TiffImagePlugin.ImageFileDirectory_v2()
+        ifd[37000] = 100
+        ifd.tagtype[37000] = TiffTags.SIGNED_RATIONAL
+
+        out = tmp_path / "temp.tif"
+        im = Image.new("L", (1, 1))
+        im.save(out, tiffinfo=ifd)
+
+        with Image.open(out) as reloaded:
+            assert reloaded.tag_v2[37000] == 100
+
     def test_ifd(self, monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> None:
         monkeypatch.setattr(TiffImagePlugin, "WRITE_LIBTIFF", True)
 

src/encode.c

@@ -1002,7 +1002,7 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) {
                 status = ImagingLibTiffSetField(
                     &encoder->state, (ttag_t)key_int, PyBytes_AsString(value)
                 );
-            } else if (type == TIFF_RATIONAL) {
+            } else if (type == TIFF_SRATIONAL || type == TIFF_RATIONAL) {
                 status = ImagingLibTiffSetField(
                     &encoder->state, (ttag_t)key_int, (FLOAT64)PyFloat_AsDouble(value)
                 );