Improve encoding of TIFF tags (#3861)

* Improve encoding of TIFF tags

- Pass tagtype from v2 directory to libtiff encoder, instead of
autodetecting type.
- Use explicit types. E.g. uint32_t for TIFF_LONG to fix issues on
platforms with 64bit longs.
- Add support for multiple values (arrays). Requires type in v2
directory and values must be passed as a tuple.
- Add support for signed types (e.g. TIFFTypes.TIFF_SIGNED_SHORT).

Co-authored-by: Andrew Murray <radarhere@users.noreply.github.com>

Tests/test_file_libtiff.py

@@ -3,6 +3,7 @@ from .helper import PillowTestCase, hopper
 from PIL import features
 from PIL._util import py3
 
+from collections import namedtuple
 from ctypes import c_float
 import io
 import logging
@@ -235,12 +236,39 @@ class TestFileLibTiff(LibTiffTestCase):
         TiffImagePlugin.WRITE_LIBTIFF = False
 
     def test_custom_metadata(self):
+        tc = namedtuple("test_case", "value,type,supported_by_default")
         custom = {
-            37000: [4, TiffTags.SHORT],
-            37001: [4.2, TiffTags.RATIONAL],
-            37002: ["custom tag value", TiffTags.ASCII],
-            37003: [u"custom tag value", TiffTags.ASCII],
-            37004: [b"custom tag value", TiffTags.BYTE],
+            37000 + k: v
+            for k, v in enumerate(
+                [
+                    tc(4, TiffTags.SHORT, True),
+                    tc(123456789, TiffTags.LONG, True),
+                    tc(-4, TiffTags.SIGNED_BYTE, False),
+                    tc(-4, TiffTags.SIGNED_SHORT, False),
+                    tc(-123456789, TiffTags.SIGNED_LONG, False),
+                    tc(TiffImagePlugin.IFDRational(4, 7), TiffTags.RATIONAL, True),
+                    tc(4.25, TiffTags.FLOAT, True),
+                    tc(4.25, TiffTags.DOUBLE, True),
+                    tc("custom tag value", TiffTags.ASCII, True),
+                    tc(u"custom tag value", TiffTags.ASCII, True),
+                    tc(b"custom tag value", TiffTags.BYTE, True),
+                    tc((4, 5, 6), TiffTags.SHORT, True),
+                    tc((123456789, 9, 34, 234, 219387, 92432323), TiffTags.LONG, True),
+                    tc((-4, 9, 10), TiffTags.SIGNED_BYTE, False),
+                    tc((-4, 5, 6), TiffTags.SIGNED_SHORT, False),
+                    tc(
+                        (-123456789, 9, 34, 234, 219387, -92432323),
+                        TiffTags.SIGNED_LONG,
+                        False,
+                    ),
+                    tc((4.25, 5.25), TiffTags.FLOAT, True),
+                    tc((4.25, 5.25), TiffTags.DOUBLE, True),
+                    # array of TIFF_BYTE requires bytes instead of tuple for backwards
+                    # compatibility
+                    tc(bytes([4]), TiffTags.BYTE, True),
+                    tc(bytes((4, 9, 10)), TiffTags.BYTE, True),
+                ]
+            )
         }
 
         libtiff_version = TiffImagePlugin._libtiff_version()
@@ -263,8 +291,13 @@ class TestFileLibTiff(LibTiffTestCase):
                 reloaded = Image.open(out)
                 for tag, value in tiffinfo.items():
                     reloaded_value = reloaded.tag_v2[tag]
-                    if isinstance(reloaded_value, TiffImagePlugin.IFDRational):
-                        reloaded_value = float(reloaded_value)
+                    if (
+                        isinstance(reloaded_value, TiffImagePlugin.IFDRational)
+                        and libtiff
+                    ):
+                        # libtiff does not support real RATIONALS
+                        self.assertAlmostEqual(float(reloaded_value), float(value))
+                        continue
 
                     if libtiff and isinstance(value, bytes):
                         value = value.decode()
@@ -274,12 +307,19 @@ class TestFileLibTiff(LibTiffTestCase):
             # Test with types
             ifd = TiffImagePlugin.ImageFileDirectory_v2()
             for tag, tagdata in custom.items():
-                ifd[tag] = tagdata[0]
-                ifd.tagtype[tag] = tagdata[1]
+                ifd[tag] = tagdata.value
+                ifd.tagtype[tag] = tagdata.type
             check_tags(ifd)
 
-            # Test without types
-            check_tags({tag: tagdata[0] for tag, tagdata in custom.items()})
+            # Test without types. This only works for some types, int for example are
+            # always encoded as LONG and not SIGNED_LONG.
+            check_tags(
+                {
+                    tag: tagdata.value
+                    for tag, tagdata in custom.items()
+                    if tagdata.supported_by_default
+                }
+            )
         TiffImagePlugin.WRITE_LIBTIFF = False
 
     def test_int_dpi(self):

docs/handbook/image-file-formats.rst

@@ -716,14 +716,20 @@ The :py:meth:`~PIL.Image.Image.save` method can take the following keyword argum
     :py:class:`~PIL.TiffImagePlugin.ImageFileDirectory_v1` object may
     be passed in this field. However, this is deprecated.
 
-    .. versionadded:: 3.0.0
+    .. versionadded:: 5.4.0
 
- .. note::
-
-    Only some tags are currently supported when writing using
+    Previous versions only supported some tags when writing using
     libtiff. The supported list is found in
     :py:attr:`~PIL:TiffTags.LIBTIFF_CORE`.
 
+    .. versionadded:: 6.1.0
+
+    Added support for signed types (e.g. ``TIFF_SIGNED_LONG``) and multiple values.
+    Multiple values for a single tag must be to
+    :py:class:`~PIL.TiffImagePlugin.ImageFileDirectory_v2` as a tuple and
+    require a matching type in
+    :py:attr:`~PIL.TiffImagePlugin.ImageFileDirectory_v2.tagtype` tagtype.
+
 **compression**
     A string containing the desired compression method for the
     file. (valid only with libtiff installed) Valid compression

src/PIL/TiffImagePlugin.py

@@ -99,6 +99,7 @@ X_RESOLUTION = 282
 Y_RESOLUTION = 283
 PLANAR_CONFIGURATION = 284
 RESOLUTION_UNIT = 296
+TRANSFERFUNCTION = 301
 SOFTWARE = 305
 DATE_TIME = 306
 ARTIST = 315
@@ -108,6 +109,7 @@ TILEOFFSETS = 324
 EXTRASAMPLES = 338
 SAMPLEFORMAT = 339
 JPEGTABLES = 347
+REFERENCEBLACKWHITE = 532
 COPYRIGHT = 33432
 IPTC_NAA_CHUNK = 33723  # newsphoto properties
 PHOTOSHOP_CHUNK = 34377  # photoshop properties
@@ -1538,9 +1540,24 @@ def _save(im, fp, filename):
             except io.UnsupportedOperation:
                 pass
 
+        # optional types for non core tags
+        types = {}
+        # SAMPLEFORMAT is determined by the image format and should not be copied
+        # from legacy_ifd.
         # STRIPOFFSETS and STRIPBYTECOUNTS are added by the library
         # based on the data in the strip.
-        blocklist = [STRIPOFFSETS, STRIPBYTECOUNTS, SAMPLEFORMAT]
+        # The other tags expect arrays with a certain length (fixed or depending on
+        # 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,
+            STRIPOFFSETS,
+            TRANSFERFUNCTION,
+        ]
+
         atts = {}
         # bits per sample is a single short in the tiff directory, not a list.
         atts[BITSPERSAMPLE] = bits[0]
@@ -1555,15 +1572,19 @@ def _save(im, fp, filename):
         ):
             # Libtiff can only process certain core items without adding
             # them to the custom dictionary.
-            # Support for custom items has only been been added
-            # for int, float, unicode, string and byte values
+            # 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 TiffTags.lookup(tag).type == TiffTags.UNDEFINED:
                     continue
-                if (
-                    distutils.version.StrictVersion(_libtiff_version())
-                    < distutils.version.StrictVersion("4.0")
-                ) or not (
+                if distutils.version.StrictVersion(
+                    _libtiff_version()
+                ) < distutils.version.StrictVersion("4.0"):
+                    continue
+
+                if tag in ifd.tagtype:
+                    types[tag] = ifd.tagtype[tag]
+                elif not (
                     isinstance(value, (int, float, str, bytes))
                     or (not py3 and isinstance(value, unicode))  # noqa: F821
                 ):
@@ -1586,7 +1607,7 @@ def _save(im, fp, filename):
         if im.mode in ("I;16B", "I;16"):
             rawmode = "I;16N"
 
-        a = (rawmode, compression, _fp, filename, atts)
+        a = (rawmode, compression, _fp, filename, atts, types)
         e = Image._getencoder(im.mode, "libtiff", a, im.encoderconfig)
         e.setimage(im.im, (0, 0) + im.size)
         while True:

src/encode.c

@@ -613,6 +613,310 @@ PyImaging_ZipEncoderNew(PyObject* self, PyObject* args)
 #endif
 
 
+/* -------------------------------------------------------------------- */
+/* LibTiff                                                              */
+/* -------------------------------------------------------------------- */
+
+#ifdef HAVE_LIBTIFF
+
+#include "TiffDecode.h"
+
+#include <string.h>
+
+PyObject*
+PyImaging_LibTiffEncoderNew(PyObject* self, PyObject* args)
+{
+    ImagingEncoderObject* encoder;
+
+    char* mode;
+    char* rawmode;
+    char* compname;
+    char* filename;
+    Py_ssize_t fp;
+
+    PyObject *tags, *types;
+    PyObject *key, *value;
+    Py_ssize_t pos = 0;
+    int key_int, status, is_core_tag, is_var_length, num_core_tags, i;
+    TIFFDataType type = TIFF_NOTYPE;
+    // 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,
+        339, 32997, 330, 531, 530
+    };
+
+    Py_ssize_t d_size;
+    PyObject *keys, *values;
+
+
+    if (! PyArg_ParseTuple(args, "sssnsOO", &mode, &rawmode, &compname, &fp, &filename, &tags, &types)) {
+        return NULL;
+    }
+
+    if (!PyDict_Check(tags)) {
+        PyErr_SetString(PyExc_ValueError, "Invalid tags dictionary");
+        return NULL;
+    } else {
+        d_size = PyDict_Size(tags);
+        TRACE(("dict size: %d\n", (int)d_size));
+        keys = PyDict_Keys(tags);
+        values = PyDict_Values(tags);
+        for (pos=0;pos<d_size;pos++){
+            TRACE(("  key: %d\n", (int)PyInt_AsLong(PyList_GetItem(keys,pos))));
+        }
+        pos = 0;
+    }
+    if (!PyDict_Check(types)) {
+        PyErr_SetString(PyExc_ValueError, "Invalid types dictionary");
+        return NULL;
+    }
+
+    TRACE(("new tiff encoder %s fp: %d, filename: %s \n", compname, fp, filename));
+
+    encoder = PyImaging_EncoderNew(sizeof(TIFFSTATE));
+    if (encoder == NULL)
+        return NULL;
+
+    if (get_packer(encoder, mode, rawmode) < 0)
+        return NULL;
+
+    if (! ImagingLibTiffEncodeInit(&encoder->state, filename, fp)) {
+        Py_DECREF(encoder);
+        PyErr_SetString(PyExc_RuntimeError, "tiff codec initialization failed");
+        return NULL;
+    }
+
+    num_core_tags = sizeof(core_tags) / sizeof(int);
+    for (pos = 0; pos < d_size; pos++) {
+        key = PyList_GetItem(keys, pos);
+        key_int = (int)PyInt_AsLong(key);
+        value = PyList_GetItem(values, pos);
+        status = 0;
+        is_core_tag = 0;
+        is_var_length = 0;
+        type = TIFF_NOTYPE;
+
+        for (i=0; i<num_core_tags; i++) {
+            if (core_tags[i] == key_int) {
+                is_core_tag = 1;
+                break;
+            }
+        }
+
+        if (!is_core_tag) {
+            PyObject *tag_type = PyDict_GetItem(types, key);
+            if (tag_type) {
+                int type_int = PyInt_AsLong(tag_type);
+                if (type_int >= TIFF_BYTE && type_int <= TIFF_DOUBLE) {
+                    type = (TIFFDataType)type_int;
+                }
+            }
+        }
+
+
+        if (type == TIFF_NOTYPE) {
+            // Autodetect type. Types should not be changed for backwards
+            // compatibility.
+            if (PyInt_Check(value)) {
+                type = TIFF_LONG;
+            } else if (PyFloat_Check(value)) {
+                type = TIFF_DOUBLE;
+            } else if (PyBytes_Check(value)) {
+                type = TIFF_ASCII;
+            }
+        }
+
+        if (PyBytes_Check(value) &&
+                (type == TIFF_BYTE || type == TIFF_UNDEFINED)) {
+            // For backwards compatibility
+            type = TIFF_ASCII;
+        }
+
+        if (PyTuple_Check(value)) {
+            Py_ssize_t len;
+            len = PyTuple_Size(value);
+
+            is_var_length = 1;
+
+            if (!len) {
+                continue;
+            }
+
+            if (type == TIFF_NOTYPE) {
+                // Autodetect type based on first item. Types should not be
+                // changed for backwards compatibility.
+                if (PyInt_Check(PyTuple_GetItem(value,0))) {
+                    type = TIFF_LONG;
+                } else if (PyFloat_Check(PyTuple_GetItem(value,0))) {
+                    type = TIFF_FLOAT;
+                }
+            }
+        }
+
+        if (!is_core_tag) {
+            // Register field for non core tags.
+            if (ImagingLibTiffMergeFieldInfo(&encoder->state, type, key_int, is_var_length)) {
+                continue;
+            }
+        }
+
+        if (is_var_length) {
+            Py_ssize_t len,i;
+            TRACE(("Setting from Tuple: %d \n", key_int));
+            len = PyTuple_Size(value);
+
+            if (type == TIFF_BYTE) {
+                UINT8 *av;
+                /* malloc check ok, calloc checks for overflow */
+                av = calloc(len, sizeof(UINT8));
+                if (av) {
+                    for (i=0;i<len;i++) {
+                        av[i] = (UINT8)PyInt_AsLong(PyTuple_GetItem(value,i));
+                    }
+                    status = ImagingLibTiffSetField(&encoder->state, (ttag_t) key_int, len, av);
+                    free(av);
+                }
+            } else if (type == TIFF_SHORT) {
+                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)PyInt_AsLong(PyTuple_GetItem(value,i));
+                    }
+                    status = ImagingLibTiffSetField(&encoder->state, (ttag_t) key_int, len, av);
+                    free(av);
+                }
+            } else if (type == TIFF_LONG) {
+                UINT32 *av;
+                /* malloc check ok, calloc checks for overflow */
+                av = calloc(len, sizeof(UINT32));
+                if (av) {
+                    for (i=0;i<len;i++) {
+                        av[i] = (UINT32)PyInt_AsLong(PyTuple_GetItem(value,i));
+                    }
+                    status = ImagingLibTiffSetField(&encoder->state, (ttag_t) key_int, len, av);
+                    free(av);
+                }
+            } else if (type == TIFF_SBYTE) {
+                INT8 *av;
+                /* malloc check ok, calloc checks for overflow */
+                av = calloc(len, sizeof(INT8));
+                if (av) {
+                    for (i=0;i<len;i++) {
+                        av[i] = (INT8)PyInt_AsLong(PyTuple_GetItem(value,i));
+                    }
+                    status = ImagingLibTiffSetField(&encoder->state, (ttag_t) key_int, len, av);
+                    free(av);
+                }
+            } else if (type == TIFF_SSHORT) {
+                INT16 *av;
+                /* malloc check ok, calloc checks for overflow */
+                av = calloc(len, sizeof(INT16));
+                if (av) {
+                    for (i=0;i<len;i++) {
+                        av[i] = (INT16)PyInt_AsLong(PyTuple_GetItem(value,i));
+                    }
+                    status = ImagingLibTiffSetField(&encoder->state, (ttag_t) key_int, len, av);
+                    free(av);
+                }
+            } else if (type == TIFF_SLONG) {
+                INT32 *av;
+                /* malloc check ok, calloc checks for overflow */
+                av = calloc(len, sizeof(INT32));
+                if (av) {
+                    for (i=0;i<len;i++) {
+                        av[i] = (INT32)PyInt_AsLong(PyTuple_GetItem(value,i));
+                    }
+                    status = ImagingLibTiffSetField(&encoder->state, (ttag_t) key_int, len, av);
+                    free(av);
+                }
+            } else if (type == TIFF_FLOAT) {
+                FLOAT32 *av;
+                /* malloc check ok, calloc checks for overflow */
+                av = calloc(len, sizeof(FLOAT32));
+                if (av) {
+                    for (i=0;i<len;i++) {
+                        av[i] = (FLOAT32)PyFloat_AsDouble(PyTuple_GetItem(value,i));
+                    }
+                    status = ImagingLibTiffSetField(&encoder->state, (ttag_t) key_int, len, av);
+                    free(av);
+                }
+            } else if (type == TIFF_DOUBLE) {
+                FLOAT64 *av;
+                /* malloc check ok, calloc checks for overflow */
+                av = calloc(len, sizeof(FLOAT64));
+                if (av) {
+                    for (i=0;i<len;i++) {
+                        av[i] = PyFloat_AsDouble(PyTuple_GetItem(value,i));
+                    }
+                    status = ImagingLibTiffSetField(&encoder->state, (ttag_t) key_int, len, av);
+                    free(av);
+                }
+            }
+        } else {
+            if (type == TIFF_SHORT) {
+                status = ImagingLibTiffSetField(&encoder->state,
+                        (ttag_t) key_int,
+                        (UINT16)PyInt_AsLong(value));
+            } else if (type == TIFF_LONG) {
+                status = ImagingLibTiffSetField(&encoder->state,
+                        (ttag_t) key_int,
+                        (UINT32)PyInt_AsLong(value));
+            } else if (type == TIFF_SSHORT) {
+                status = ImagingLibTiffSetField(&encoder->state,
+                        (ttag_t) key_int,
+                        (INT16)PyInt_AsLong(value));
+            } else if (type == TIFF_SLONG) {
+                status = ImagingLibTiffSetField(&encoder->state,
+                        (ttag_t) key_int,
+                        (INT32)PyInt_AsLong(value));
+            } else if (type == TIFF_FLOAT) {
+                status = ImagingLibTiffSetField(&encoder->state,
+                        (ttag_t) key_int,
+                        (FLOAT32)PyFloat_AsDouble(value));
+            } else if (type == TIFF_DOUBLE) {
+                status = ImagingLibTiffSetField(&encoder->state,
+                        (ttag_t) key_int,
+                        (FLOAT64)PyFloat_AsDouble(value));
+            } else if (type == TIFF_BYTE) {
+                status = ImagingLibTiffSetField(&encoder->state,
+                        (ttag_t) key_int,
+                        (UINT8)PyInt_AsLong(value));
+            } else if (type == TIFF_SBYTE) {
+                status = ImagingLibTiffSetField(&encoder->state,
+                        (ttag_t) key_int,
+                        (INT8)PyInt_AsLong(value));
+            } else if (type == TIFF_ASCII) {
+                status = ImagingLibTiffSetField(&encoder->state,
+                        (ttag_t) key_int,
+                        PyBytes_AsString(value));
+            } else if (type == TIFF_RATIONAL) {
+                status = ImagingLibTiffSetField(&encoder->state,
+                        (ttag_t) key_int,
+                        (FLOAT64)PyFloat_AsDouble(value));
+            } else {
+                TRACE(("Unhandled type for key %d : %s \n",
+                            key_int,
+                            PyBytes_AsString(PyObject_Str(value))));
+            }
+        }
+        if (!status) {
+            TRACE(("Error setting Field\n"));
+            Py_DECREF(encoder);
+            PyErr_SetString(PyExc_RuntimeError, "Error setting from dictionary");
+            return NULL;
+        }
+    }
+
+    encoder->encode  = ImagingLibTiffEncode;
+
+    return (PyObject*) encoder;
+}
+
+#endif
+
 /* -------------------------------------------------------------------- */
 /* JPEG                                                                 */
 /* -------------------------------------------------------------------- */
@@ -787,168 +1091,6 @@ PyImaging_JpegEncoderNew(PyObject* self, PyObject* args)
 
 #endif
 
-/* -------------------------------------------------------------------- */
-/* LibTiff                                                              */
-/* -------------------------------------------------------------------- */
-
-#ifdef HAVE_LIBTIFF
-
-#include "TiffDecode.h"
-
-#include <string.h>
-
-PyObject*
-PyImaging_LibTiffEncoderNew(PyObject* self, PyObject* args)
-{
-    ImagingEncoderObject* encoder;
-
-    char* mode;
-    char* rawmode;
-    char* compname;
-    char* filename;
-    Py_ssize_t fp;
-
-    PyObject *dir;
-    PyObject *key, *value;
-    Py_ssize_t pos = 0;
-    int key_int, status, is_core_tag, number_of_tags, i;
-    // This list also exists in TiffTags.py
-    const int 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,
-        339, 32997, 330, 531, 530
-    };
-
-    Py_ssize_t d_size;
-    PyObject *keys, *values;
-
-
-    if (! PyArg_ParseTuple(args, "sssnsO", &mode, &rawmode, &compname, &fp, &filename, &dir)) {
-        return NULL;
-    }
-
-    if (!PyDict_Check(dir)) {
-        PyErr_SetString(PyExc_ValueError, "Invalid Dictionary");
-        return NULL;
-    } else {
-        d_size = PyDict_Size(dir);
-        TRACE(("dict size: %d\n", (int)d_size));
-        keys = PyDict_Keys(dir);
-        values = PyDict_Values(dir);
-        for (pos=0;pos<d_size;pos++){
-            TRACE(("  key: %d\n", (int)PyInt_AsLong(PyList_GetItem(keys,pos))));
-        }
-        pos = 0;
-    }
-
-    TRACE(("new tiff encoder %s fp: %d, filename: %s \n", compname, fp, filename));
-
-    encoder = PyImaging_EncoderNew(sizeof(TIFFSTATE));
-    if (encoder == NULL)
-        return NULL;
-
-    if (get_packer(encoder, mode, rawmode) < 0)
-        return NULL;
-
-    if (! ImagingLibTiffEncodeInit(&encoder->state, filename, fp)) {
-        Py_DECREF(encoder);
-        PyErr_SetString(PyExc_RuntimeError, "tiff codec initialization failed");
-        return NULL;
-    }
-
-    number_of_tags = sizeof(tags) / sizeof(int);
-    for (pos = 0; pos < d_size; pos++) {
-        key = PyList_GetItem(keys, pos);
-        key_int = (int)PyInt_AsLong(key);
-        value = PyList_GetItem(values, pos);
-        status = 0;
-        is_core_tag = 0;
-        for (i=0; i<number_of_tags; i++) {
-            if (tags[i] == key_int) {
-                is_core_tag = 1;
-                break;
-            }
-        }
-        TRACE(("Attempting to set key: %d\n", key_int));
-        if (PyInt_Check(value)) {
-            TRACE(("Setting from Int: %d %ld \n", key_int, PyInt_AsLong(value)));
-            if (is_core_tag || !ImagingLibTiffMergeFieldInfo(&encoder->state, TIFF_LONG, key_int)) {
-                status = ImagingLibTiffSetField(&encoder->state,
-                                                (ttag_t) PyInt_AsLong(key),
-                                                PyInt_AsLong(value));
-            }
-        } else if (PyFloat_Check(value)) {
-            TRACE(("Setting from Float: %d, %f \n", key_int, PyFloat_AsDouble(value)));
-            if (is_core_tag || !ImagingLibTiffMergeFieldInfo(&encoder->state, TIFF_DOUBLE, key_int)) {
-                status = ImagingLibTiffSetField(&encoder->state,
-                                                (ttag_t) PyInt_AsLong(key),
-                                                (double)PyFloat_AsDouble(value));
-            }
-        } else if (PyBytes_Check(value)) {
-            TRACE(("Setting from Bytes: %d, %s \n", key_int, PyBytes_AsString(value)));
-            if (is_core_tag || !ImagingLibTiffMergeFieldInfo(&encoder->state, TIFF_ASCII, key_int)) {
-                status = ImagingLibTiffSetField(&encoder->state,
-                                                (ttag_t) PyInt_AsLong(key),
-                                                PyBytes_AsString(value));
-            }
-        } else if (PyTuple_Check(value)) {
-            Py_ssize_t len,i;
-            float *floatav;
-            int *intav;
-            TRACE(("Setting from Tuple: %d \n", key_int));
-            len = PyTuple_Size(value);
-            if (len) {
-                if (PyInt_Check(PyTuple_GetItem(value,0))) {
-                    TRACE((" %d elements, setting as ints \n", (int)len));
-                    /* malloc check ok, calloc checks for overflow */
-                    intav = calloc(len, sizeof(int));
-                    if (intav) {
-                        for (i=0;i<len;i++) {
-                            intav[i] = (int)PyInt_AsLong(PyTuple_GetItem(value,i));
-                        }
-                        status = ImagingLibTiffSetField(&encoder->state,
-                                                        (ttag_t) PyInt_AsLong(key),
-                                                        len, intav);
-                        free(intav);
-                    }
-                } else if (PyFloat_Check(PyTuple_GetItem(value,0))) {
-                    TRACE((" %d elements, setting as floats \n", (int)len));
-                    /* malloc check ok, calloc checks for overflow */
-                    floatav = calloc(len, sizeof(float));
-                    if (floatav) {
-                        for (i=0;i<len;i++) {
-                            floatav[i] = (float)PyFloat_AsDouble(PyTuple_GetItem(value,i));
-                        }
-                        status = ImagingLibTiffSetField(&encoder->state,
-                                                        (ttag_t) PyInt_AsLong(key),
-                                                        len, floatav);
-                        free(floatav);
-                    }
-                } else {
-                    TRACE(("Unhandled type in tuple for key %d : %s \n",
-                           key_int,
-                           PyBytes_AsString(PyObject_Str(value))));
-                }
-            }
-        } else {
-            TRACE(("Unhandled type for key %d : %s \n",
-                   key_int,
-                   PyBytes_AsString(PyObject_Str(value))));
-        }
-        if (!status) {
-            TRACE(("Error setting Field\n"));
-            Py_DECREF(encoder);
-            PyErr_SetString(PyExc_RuntimeError, "Error setting from dictionary");
-            return NULL;
-        }
-    }
-
-    encoder->encode  = ImagingLibTiffEncode;
-
-    return (PyObject*) encoder;
-}
-
-#endif
 
 /* -------------------------------------------------------------------- */
 /* JPEG	2000								*/

src/libImaging/TiffDecode.c

@@ -520,15 +520,33 @@ int ImagingLibTiffEncodeInit(ImagingCodecState state, char *filename, int fp) {
 
 }
 
-int ImagingLibTiffMergeFieldInfo(ImagingCodecState state, TIFFDataType field_type, int key){
+int ImagingLibTiffMergeFieldInfo(ImagingCodecState state, TIFFDataType field_type, int key, int is_var_length){
+    // Refer to libtiff docs (http://www.simplesystems.org/libtiff/addingtags.html)
     TIFFSTATE *clientstate = (TIFFSTATE *)state->context;
     char field_name[10];
     uint32 n;
     int status = 0;
 
-    const TIFFFieldInfo info[] = {
-        { key, 0, 1, field_type, FIELD_CUSTOM, 1, 0, field_name }
+    // custom fields added with ImagingLibTiffMergeFieldInfo are only used for
+    // decoding, ignore readcount;
+    int readcount = 0;
+    // we support writing a single value, or a variable number of values
+    int writecount = 1;
+    // whether the first value should encode the number of values.
+    int passcount = 0;
+
+    TIFFFieldInfo info[] = {
+        { key, readcount, writecount, field_type, FIELD_CUSTOM, 1, passcount, field_name }
     };
+
+    if (is_var_length) {
+        info[0].field_writecount = -1;
+    }
+
+    if (is_var_length && field_type != TIFF_ASCII) {
+        info[0].field_passcount = 1;
+    }
+
     n = sizeof(info) / sizeof(info[0]);
 
     // Test for libtiff 4.0 or later, excluding libtiff 3.9.6 and 3.9.7

src/libImaging/TiffDecode.h

@@ -45,7 +45,7 @@ typedef struct {
 
 extern int ImagingLibTiffInit(ImagingCodecState state, int fp, uint32 offset);
 extern int ImagingLibTiffEncodeInit(ImagingCodecState state, char *filename, int fp);
-extern int ImagingLibTiffMergeFieldInfo(ImagingCodecState state, TIFFDataType field_type, int key);
+extern int ImagingLibTiffMergeFieldInfo(ImagingCodecState state, TIFFDataType field_type, int key, int is_var_length);
 extern int ImagingLibTiffSetField(ImagingCodecState state, ttag_t tag, ...);