mipmap_cache: respect conf request to always use embedded thumbnail

RELEASE_NOTES.md

@@ -65,7 +65,12 @@ changes (where available).
 
 ## Bug Fixes
 
-- N/A
+- Honor the default configuration preference "never" for "use raw
+  instead of jpeg from size": for unaltered images, always generate
+  thumbnails/previews from embedded JPEGs rather than processing the
+  raw file. If you prefer the prior behavior, which processed the raw
+  file rather than upscale the embedded JPEG for higher resolution
+  thumbnails/previews, use the new configuration option "auto".
 
 ## Lua
 

data/darktableconfig.xml.in

@@ -1332,7 +1332,7 @@
   </dtconfig>
   <dtconfig prefs="lighttable" section="thumbs">
     <name>plugins/lighttable/thumbnail_raw_min_level</name>
-   <type>
+    <type>
       <enum>
         <option>always</option>
         <option>small</option>
@@ -1343,11 +1343,12 @@
         <option>4K</option>
         <option>5K</option>
         <option>never</option>
+	<option>auto</option>
       </enum>
     </type>
     <default>never</default>
-    <shortdescription>use raw file instead of embedded JPEG from size</shortdescription>
-    <longdescription>if the thumbnail size is greater than this value, it will be processed using raw file instead of the embedded preview JPEG (better but slower).\nif you want all thumbnails and pre-rendered images in best quality you should choose the *always* option.\n(more comments in the manual)</longdescription>
+    <shortdescription>for unaltered images, use raw file instead of embedded JPEG from size</shortdescription>
+    <longdescription>if the thumbnail size is greater than this value, it will be processed using raw file instead of the embedded preview JPEG (better but slower).\nif you want all thumbnails and pre-rendered images in best quality you should choose the *always* option.\nfor the quickest display, choose the *never* option\nthe *auto* option prefers the embedded JPEG except when the when thumb size exceeds the resolution of the embedded JPEG\n(more comments in the manual)</longdescription>
   </dtconfig>
   <dtconfig prefs="lighttable" section="thumbs">
     <name>plugins/lighttable/thumbnail_hq_min_level</name>

src/common/mipmap_cache.c

@@ -1,6 +1,6 @@
 /*
     This file is part of darktable,
-    Copyright (C) 2011-2025 darktable developers.
+    Copyright (C) 2011-2026 darktable developers.
 
     darktable is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -1215,6 +1215,7 @@ dt_mipmap_size_t dt_mipmap_cache_get_min_mip_from_pref(const char *value)
   if(strcmp(value, "WQXGA") == 0)  return DT_MIPMAP_5;
   if(strcmp(value, "4K") == 0)     return DT_MIPMAP_6;
   if(strcmp(value, "5K") == 0)     return DT_MIPMAP_7;
+  if(strcmp(value, "auto") == 0)   return DT_MIPMAP_8;
   return DT_MIPMAP_NONE;
 }
 
@@ -1504,16 +1505,16 @@ static void _init_8(uint8_t *buf,
       res = dt_imageio_large_thumbnail(filename, &tmp, &thumb_width, &thumb_height, color_space);
       if(!res)
       {
-        // if the thumbnail is not large enough, we compute one
+        // use embedded JPEG if it is large enough or conf requests
+        // always use, otherwise compute one
         const dt_image_t *img2 = dt_image_cache_get(imgid, 'r');
         const int imgwd = img2->width;
         const int imght = img2->height;
         dt_image_cache_read_release(img2);
-        if(thumb_width < wd
-           && thumb_height < ht
-           && thumb_width < imgwd - 4
-           && thumb_height < imght - 4)
-        {
+        const gboolean always_use_thumb = (min_s == DT_MIPMAP_NONE);
+        const gboolean thumb_lt_mip = ((thumb_width < wd) && (thumb_height < ht));
+        const gboolean thumb_lt_raw = ((thumb_width < imgwd - 4) && (thumb_height < imght - 4));
+        if (!always_use_thumb && thumb_lt_mip && thumb_lt_raw) {
           res = TRUE;
         }
         else

src/dtgtk/culling.c

@@ -1,6 +1,6 @@
 /*
     This file is part of darktable,
-    Copyright (C) 2020-2023 darktable developers.
+    Copyright (C) 2020-2026 darktable developers.
 
     darktable is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -1155,8 +1155,10 @@ static void _thumbs_prefetch(dt_culling_t *table)
     maxw = MAX(maxw, th->width);
     maxh = MAX(maxh, th->height);
   }
+  const int32_t mipwidth = maxw * darktable.gui->ppd;
+  const int32_t mipheight = maxh * darktable.gui->ppd;
   dt_mipmap_size_t mip =
-    dt_mipmap_cache_get_matching_size(maxw, maxh);
+    dt_mipmap_cache_get_matching_size(mipwidth, mipheight);
 
   // prefetch next image
   gchar *query;

src/dtgtk/thumbtable.c

@@ -1669,13 +1669,13 @@ static void _thumbs_ask_for_discard(dt_thumbtable_t *table)
     dt_conf_get_string_const("plugins/lighttable/thumbnail_hq_min_level");
   dt_mipmap_size_t hql =
     dt_mipmap_cache_get_min_mip_from_pref(hq);
+
   const char *embedded =
     dt_conf_get_string_const("plugins/lighttable/thumbnail_raw_min_level");
-
   dt_mipmap_size_t embeddedl = dt_mipmap_cache_get_min_mip_from_pref(embedded);
 
-  int min_level = 8;
-  int max_level = 0;
+  int min_level = DT_MIPMAP_8;
+  int max_level = DT_MIPMAP_0;
   if(hql != table->pref_hq)
   {
     min_level = MIN(table->pref_hq, hql);
@@ -1687,6 +1687,15 @@ static void _thumbs_ask_for_discard(dt_thumbtable_t *table)
     max_level = MAX(max_level, MAX(table->pref_embedded, embeddedl));
   }
 
+  // switching between auto/never options
+  if (max_level == DT_MIPMAP_NONE && min_level == DT_MIPMAP_8)
+  {
+    // err on side of discarding too many thumbnails: a quick
+    // survey of vintage raw files shows a lowest res embedded
+    // JPEG of 1616x1080 (found in 2011 & 2014 Sony)
+    min_level = DT_MIPMAP_4;
+  }
+
   sqlite3_stmt *stmt = NULL;
 
   if(min_level < max_level)
@@ -1722,7 +1731,7 @@ static void _thumbs_ask_for_discard(dt_thumbtable_t *table)
       while(sqlite3_step(stmt) == SQLITE_ROW)
       {
         const dt_imgid_t imgid = sqlite3_column_int(stmt, 0);
-        for(int i = max_level - 1; i >= min_level; i--)
+        for(int i = max_level; i >= min_level; i--)
         {
           dt_mipmap_cache_remove_at_size(imgid, i);
         }