From 100a72ca3c2bfa3b9b595c3f980eae198de20e41 Mon Sep 17 00:00:00 2001
From: Andrii Ryzhkov <andrii.ryzhkov@pm.me>
Date: Wed, 29 Apr 2026 11:26:14 +0200
Subject: [PATCH 1/2] Fix corrupt DNG on libtiff builds that drop CFA tag info
 across SubIFD write

---
 src/imageio/imageio_dng.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/imageio/imageio_dng.c b/src/imageio/imageio_dng.c
index 8d1c65addf70..010b0071fa27 100644
--- a/src/imageio/imageio_dng.c
+++ b/src/imageio/imageio_dng.c
@@ -184,10 +184,11 @@ int dt_imageio_dng_write_cfa_bayer(const char *filename,
       g_unlink(filename);
       return 1;
     }
-    // libtiff entered INSUBIFD mode when the IFD0 carrying TIFFTAG_SUBIFD
-    // was written; subsequent TIFFSetField + scanline writes populate
-    // the SubIFD without an explicit TIFFCreateDirectory call (whose
-    // return-value convention changed between libtiff versions)
+    // re-register default tag info on some libtiff builds CFA/DNG
+    // extension tags would be lost across the IFD write, breaking
+    // CFAREPEATPATTERNDIM / CFAPATTERN. return value differs across
+    // libtiff versions; not checked
+    TIFFCreateDirectory(tif);
   }
 
   // raw payload IFD: single IFD when no preview, otherwise SubIFD0
@@ -321,7 +322,9 @@ int dt_imageio_dng_write_linear(const char *filename,
       g_unlink(filename);
       return 1;
     }
-    // libtiff is in INSUBIFD mode after IFD0 was written with TIFFTAG_SUBIFD
+    // re-initialize directory state so DNG extension tag info is
+    // available on the SubIFD (see comment in write_cfa_bayer)
+    TIFFCreateDirectory(tif);
   }
 
   // baseline TIFF tags, 3 samples per pixel (demosaicked)

From d5af7b6b37df48871a030a16fad0a1edc897ccb8 Mon Sep 17 00:00:00 2001
From: Andrii Ryzhkov <andrii.ryzhkov@pm.me>
Date: Wed, 29 Apr 2026 11:54:17 +0200
Subject: [PATCH 2/2] Add libtiff error handlers in DNG writer to avoid
 third-party handler crashes

---
 src/imageio/imageio_dng.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/src/imageio/imageio_dng.c b/src/imageio/imageio_dng.c
index 010b0071fa27..429c3723e4fc 100644
--- a/src/imageio/imageio_dng.c
+++ b/src/imageio/imageio_dng.c
@@ -39,6 +39,38 @@
 // these as float/double arrays and handles the conversion; we just pass
 // the values as double
 
+// libtiff error/warning handlers — replacing whatever else in the
+// process may have installed (e.g. ImageMagick's, which crashes on
+// NULL exception context). these just log to stderr and never abort
+static void _dt_dng_tiff_warning(const char *module,
+                                 const char *fmt, va_list ap)
+{
+  if(darktable.unmuted & DT_DEBUG_IMAGEIO)
+  {
+    fprintf(stderr, "%11.4f [imageio_dng] warning: %s: ",
+            dt_get_wtime() - darktable.start_wtime,
+            module ? module : "(none)");
+    vfprintf(stderr, fmt, ap);
+    fprintf(stderr, "\n");
+  }
+}
+
+static void _dt_dng_tiff_error(const char *module,
+                               const char *fmt, va_list ap)
+{
+  fprintf(stderr, "%11.4f [imageio_dng] error: %s: ",
+          dt_get_wtime() - darktable.start_wtime,
+          module ? module : "(none)");
+  vfprintf(stderr, fmt, ap);
+  fprintf(stderr, "\n");
+}
+
+static void _install_dng_tiff_handlers(void)
+{
+  TIFFSetWarningHandler(_dt_dng_tiff_warning);
+  TIFFSetErrorHandler(_dt_dng_tiff_error);
+}
+
 // map the dcraw 2x2 CFA filters word to 4 single-byte channel indices
 // for the DNG CFAPattern tag: 0=R, 1=G, 2=B, following DNG spec §A.3.1
 static void _cfa_bytes_from_filters(uint32_t filters, uint8_t out[4])
@@ -160,6 +192,8 @@ int dt_imageio_dng_write_cfa_bayer(const char *filename,
   if(!filename || !cfa || !img || width <= 0 || height <= 0)
     return 1;
 
+  _install_dng_tiff_handlers();
+
 #ifdef _WIN32
   wchar_t *wfilename = g_utf8_to_utf16(filename, -1, NULL, NULL, NULL);
   TIFF *tif = TIFFOpenW(wfilename, "wl");
@@ -300,6 +334,8 @@ int dt_imageio_dng_write_linear(const char *filename,
   if(!filename || !rgb || !img || width <= 0 || height <= 0)
     return 1;
 
+  _install_dng_tiff_handlers();
+
 #ifdef _WIN32
   wchar_t *wfilename = g_utf8_to_utf16(filename, -1, NULL, NULL, NULL);
   TIFF *tif = TIFFOpenW(wfilename, "wl");