From 28f3e9f6a2ce889ceb8764afb4cc17b9bb5d65f8 Mon Sep 17 00:00:00 2001
From: deekayhd <53017684+deekayhd@users.noreply.github.com>
Date: Sun, 29 Mar 2026 14:29:39 +0200
Subject: [PATCH 1/4] fix wrong month in EXIF.MONTH.LONG and EXIF_MONTH.SHORT
 when no date available

---
 lib/dtutils/string.lua | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/dtutils/string.lua b/lib/dtutils/string.lua
index 9a1085f..3f84643 100644
--- a/lib/dtutils/string.lua
+++ b/lib/dtutils/string.lua
@@ -774,6 +774,7 @@ function dtutils_string.build_substitute_list(image, sequence, variable_string,
   local labels = get_colorlabels(image)
 
   local datetime_taken = ""
+  local emon_long, emon_short
   local use_millisecs = false
   if dt.preferences.read("darktable", "lighttable/ui/milliseconds", "bool") and is_api_9_1 then
     use_millisecs = true
@@ -781,12 +782,16 @@ function dtutils_string.build_substitute_list(image, sequence, variable_string,
 
   if image.exif_datetime_taken and image.exif_datetime_taken ~= "" then
     datetime_taken = image.exif_datetime_taken
+    emon_long = os.date("%B", exiftime2systime(datetime_taken))
+    emon_short = os.date("%b", exiftime2systime(datetime_taken))
   else
     if use_millisecs then
       datetime_taken = "0000:00:00 00:00:00.0"
     else
       datetime_taken = "0000:00:00 00:00:00"
     end
+    emon_long = _("unknown")
+    emon_short = "???"
   end
 
   local eyear, emon, eday, ehour, emin, esec, emsec
@@ -840,8 +845,8 @@ function dtutils_string.build_substitute_list(image, sequence, variable_string,
                         eyear,                                 -- EXIF.YEAR
                         string.sub(eyear, 3),                  -- EXIF.YEAR.SHORT
                         emon,                                  -- EXIF.MONTH
-                        os.date("%B", exiftime2systime(datetime_taken)), -- EXIF.MONTH.LONG
-                        os.date("%b", exiftime2systime(datetime_taken)), -- EXIF.MONTH.SHORT
+                        emon_long,                             -- EXIF.MONTH.LONG
+                        emon_short,                            -- EXIF.MONTH.SHORT
                         eday,                                  -- EXIF.DAY
                         ehour,                                 -- EXIF.HOUR
                         "",                                    -- EXIF.HOUR.AMPM

From af362315e8df30621e441943a9d9a2598dc131f2 Mon Sep 17 00:00:00 2001
From: deekayhd <53017684+deekayhd@users.noreply.github.com>
Date: Sun, 29 Mar 2026 23:07:25 +0200
Subject: [PATCH 2/4] set all vars derived from datetime_taken to ""

---
 lib/dtutils/string.lua | 27 +++++++++------------------
 1 file changed, 9 insertions(+), 18 deletions(-)

diff --git a/lib/dtutils/string.lua b/lib/dtutils/string.lua
index 3f84643..59dbb77 100644
--- a/lib/dtutils/string.lua
+++ b/lib/dtutils/string.lua
@@ -773,8 +773,8 @@ function dtutils_string.build_substitute_list(image, sequence, variable_string,
 
   local labels = get_colorlabels(image)
 
-  local datetime_taken = ""
   local emon_long, emon_short
+  local eyear, emon, eday, ehour, emin, esec, emsec
   local use_millisecs = false
   if dt.preferences.read("darktable", "lighttable/ui/milliseconds", "bool") and is_api_9_1 then
     use_millisecs = true
@@ -784,27 +784,18 @@ function dtutils_string.build_substitute_list(image, sequence, variable_string,
     datetime_taken = image.exif_datetime_taken
     emon_long = os.date("%B", exiftime2systime(datetime_taken))
     emon_short = os.date("%b", exiftime2systime(datetime_taken))
-  else
     if use_millisecs then
-      datetime_taken = "0000:00:00 00:00:00.0"
+      eyear, emon, eday, ehour, emin, esec, emsec = 
+        string.match(datetime_taken, "(%d+):(%d+):(%d+) (%d+):(%d+):(%d+)%.(%d+)$")
     else
-      datetime_taken = "0000:00:00 00:00:00"
-    end
-    emon_long = _("unknown")
-    emon_short = "???"
-  end
-
-  local eyear, emon, eday, ehour, emin, esec, emsec
-  if use_millisecs then
-    eyear, emon, eday, ehour, emin, esec, emsec = 
-      string.match(datetime_taken, "(%d+):(%d+):(%d+) (%d+):(%d+):(%d+)%.(%d+)$")
+      emsec = "0"
+      eyear, emon, eday, ehour, emin, esec = 
+        string.match(datetime_taken, "(%d+):(%d+):(%d+) (%d+):(%d+):(%d+)$")
+    end    
   else
-    emsec = "0"
-    eyear, emon, eday, ehour, emin, esec = 
-      string.match(datetime_taken, "(%d+):(%d+):(%d+) (%d+):(%d+):(%d+)$")
+    emon_long, emon_short, eyear, emon, eday, ehour, emin, esec, emsec = ""
   end
 
-
   local version_multi = #image:get_group_members() > 1 and image.duplicate_index or ""
 
   local replacements = {dtutils_string.get_basename(image.film.path),-- ROLL.NAME
@@ -843,7 +834,7 @@ function dtutils_string.build_substitute_list(image, sequence, variable_string,
                         string.format("%02d", datetime.sec),   -- SECOND
                         0,                                     -- MSEC
                         eyear,                                 -- EXIF.YEAR
-                        string.sub(eyear, 3),                  -- EXIF.YEAR.SHORT
+                        (eyear ~= nil) and string.sub(eyear, 3) or "", -- EXIF.YEAR.SHORT
                         emon,                                  -- EXIF.MONTH
                         emon_long,                             -- EXIF.MONTH.LONG
                         emon_short,                            -- EXIF.MONTH.SHORT

From 80ff1ef0aaac87e13b95a84fa6bf674661a8197f Mon Sep 17 00:00:00 2001
From: deekayhd <53017684+deekayhd@users.noreply.github.com>
Date: Sun, 29 Mar 2026 23:33:23 +0200
Subject: [PATCH 3/4] add warning message

---
 lib/dtutils/string.lua | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/dtutils/string.lua b/lib/dtutils/string.lua
index 59dbb77..38a17f4 100644
--- a/lib/dtutils/string.lua
+++ b/lib/dtutils/string.lua
@@ -793,6 +793,7 @@ function dtutils_string.build_substitute_list(image, sequence, variable_string,
         string.match(datetime_taken, "(%d+):(%d+):(%d+) (%d+):(%d+):(%d+)$")
     end    
   else
+    log.msg(log.warn, "no capture datetime found in EXIF data")
     emon_long, emon_short, eyear, emon, eday, ehour, emin, esec, emsec = ""
   end
 

From 4d3924939bde280dbd2e281e6881d732276e106d Mon Sep 17 00:00:00 2001
From: deekayhd <53017684+deekayhd@users.noreply.github.com>
Date: Sun, 29 Mar 2026 23:45:40 +0200
Subject: [PATCH 4/4] remove unnecessary variable datetime_taken

---
 lib/dtutils/string.lua | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/lib/dtutils/string.lua b/lib/dtutils/string.lua
index 38a17f4..c03bd66 100644
--- a/lib/dtutils/string.lua
+++ b/lib/dtutils/string.lua
@@ -781,9 +781,8 @@ function dtutils_string.build_substitute_list(image, sequence, variable_string,
   end
 
   if image.exif_datetime_taken and image.exif_datetime_taken ~= "" then
-    datetime_taken = image.exif_datetime_taken
-    emon_long = os.date("%B", exiftime2systime(datetime_taken))
-    emon_short = os.date("%b", exiftime2systime(datetime_taken))
+    emon_long = os.date("%B", exiftime2systime(image.exif_datetime_taken))
+    emon_short = os.date("%b", exiftime2systime(image.exif_datetime_taken))
     if use_millisecs then
       eyear, emon, eday, ehour, emin, esec, emsec = 
         string.match(datetime_taken, "(%d+):(%d+):(%d+) (%d+):(%d+):(%d+)%.(%d+)$")
@@ -793,7 +792,7 @@ function dtutils_string.build_substitute_list(image, sequence, variable_string,
         string.match(datetime_taken, "(%d+):(%d+):(%d+) (%d+):(%d+):(%d+)$")
     end    
   else
-    log.msg(log.warn, "no capture datetime found in EXIF data")
+    log.msg(log.warn, "no capture date and time found in EXIF data")
     emon_long, emon_short, eyear, emon, eday, ehour, emin, esec, emsec = ""
   end