Commit 07883df96 for imagemagick.org

commit 07883df968f66c97e159e4c27f80c324402f7620
Author: Dirk Lemstra <dirk@lemstra.org>
Date:   Sun Oct 25 17:33:14 2026 +0100

    Correct encoding with group4 compression in tiff coder (#9058).

diff --git a/coders/tiff.c b/coders/tiff.c
index 2ebc4702d..7b799dca6 100644
--- a/coders/tiff.c
+++ b/coders/tiff.c
@@ -3639,13 +3639,16 @@ static MagickBooleanType WriteTIFFImage(const ImageInfo *image_info,
       case FaxCompression:
       case Group4Compression:
       {
-        if (IsImageMonochrome(image) == MagickFalse)
-          {
-            if (IsImageGray(image) == MagickFalse)
-              (void) SetImageType(image,BilevelType,exception);
-            else
-              (void) SetImageDepth(image,1,exception);
-          }
+        if (image->alpha_trait != UndefinedPixelTrait)
+          (void) SetImageType(image,BilevelType,exception);
+        else
+          if (IsImageMonochrome(image) == MagickFalse)
+            {
+              if (IsImageGray(image) == MagickFalse)
+                (void) SetImageType(image,BilevelType,exception);
+              else
+                (void) SetImageDepth(image,1,exception);
+            }
         image->depth=1;
         image->number_meta_channels=0;
         break;
diff --git a/tests/Makefile.am b/tests/Makefile.am
index a2f8cb8fc..42df0d7bd 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -46,6 +46,7 @@ TESTS_TESTS = \
   tests/cli-pipe.tap \
   tests/cli-svg.tap \
   tests/cli-statistic.tap \
+  tests/cli-tiff.tap \
   tests/cli-uhdr.tap \
   tests/cli-uhdr-encoder.tap \
   tests/cli-uhdr-resize-filter.tap \
diff --git a/tests/cli-tiff.tap b/tests/cli-tiff.tap
new file mode 100644
index 000000000..4906040ef
--- /dev/null
+++ b/tests/cli-tiff.tap
@@ -0,0 +1,29 @@
+#!/bin/sh
+#
+#  Copyright 1999 ImageMagick Studio LLC, a non-profit organization
+#  dedicated to making software imaging solutions freely available.
+#
+#  You may not use this file except in compliance with the License.  You may
+#  obtain a copy of the License at
+#
+#    https://imagemagick.org/license/
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+#  Regression tests for TIFF.
+#
+. ./common.shi
+. ${srcdir}/tests/common.shi
+echo "1..1"
+
+${MAGICK} -size 100x100 xc:white -alpha set -colorspace gray \
+  -threshold 50% -compress group4 tiff_group4_alpha.tiff &&
+  [ "$(${IDENTIFY} -format "%C %[channels]" tiff_group4_alpha.tiff)" = \
+    "Group4 gray" ] && echo "ok" || echo "not ok"
+
+rm -f tiff_group4_alpha.tiff
+: