feat(avif): add chroma subsampling control for AVIF export (#19595)

* feat(avif): add chroma subsampling control for AVIF export

Add a new chroma subsampling option to the AVIF export module, allowing users to manually select subsampling modes (4:4:4, 4:2:2, 4:2:0) or use auto mode based on quality thresholds. This provides finer control over compression and quality trade-offs in AVIF images.

* feat(avif): add chroma subsampling configuration

Add a new configuration option for AVIF chroma subsampling in the imageio plugin settings. This allows users to control subsampling levels (0-3) for AVIF exports, defaulting to 0.

* feat(avif): conditionally disable chroma subsampling UI for lossless mode

When AVIF compression is set to lossless, the subsample control is now hidden from the GUI to prevent irrelevant options, and marked with no-show-all for better layout management. This improves user experience by simplifying the interface during lossless exports.

Author: kadykov

data/darktableconfig.xml.in

@@ -2913,6 +2913,13 @@
     <shortdescription/>
     <longdescription/>
   </dtconfig>
+  <dtconfig>
+    <name>plugins/imageio/format/avif/subsample</name>
+    <type min="0" max="3">int</type>
+    <default>0</default>
+    <shortdescription>AVIF chroma subsampling</shortdescription>
+    <longdescription/>
+  </dtconfig>
   <dtconfig>
     <name>plugins/imageio/format/xcf/bpp</name>
     <type>

src/imageio/format/avif.c

@@ -51,6 +51,14 @@ enum avif_tiling_e
   AVIF_TILING_OFF
 };
 
+enum avif_subsample_e
+{
+  AVIF_SUBSAMPLE_AUTO = 0,
+  AVIF_SUBSAMPLE_444,
+  AVIF_SUBSAMPLE_422,
+  AVIF_SUBSAMPLE_420
+};
+
 enum avif_color_mode_e
 {
   AVIF_COLOR_MODE_RGB = 0,
@@ -65,6 +73,7 @@ typedef struct dt_imageio_avif_t
   uint32_t compression_type;
   uint32_t quality;
   uint32_t tiling;
+  uint32_t subsample;
 } dt_imageio_avif_t;
 
 typedef struct dt_imageio_avif_gui_t
@@ -74,6 +83,7 @@ typedef struct dt_imageio_avif_gui_t
   GtkWidget *compression_type;
   GtkWidget *quality;
   GtkWidget *tiling;
+  GtkWidget *subsample;
 } dt_imageio_avif_gui_t;
 
 static const struct
@@ -207,6 +217,28 @@ void init(dt_imageio_module_format_t *self)
                                 dt_imageio_avif_t,
                                 quality,
                                 int);
+
+  /* subsample */
+  luaA_enum(darktable.lua_state.state,
+            enum avif_subsample_e);
+  luaA_enum_value(darktable.lua_state.state,
+                  enum avif_subsample_e,
+                  AVIF_SUBSAMPLE_AUTO);
+  luaA_enum_value(darktable.lua_state.state,
+                  enum avif_subsample_e,
+                  AVIF_SUBSAMPLE_444);
+  luaA_enum_value(darktable.lua_state.state,
+                  enum avif_subsample_e,
+                  AVIF_SUBSAMPLE_422);
+  luaA_enum_value(darktable.lua_state.state,
+                  enum avif_subsample_e,
+                  AVIF_SUBSAMPLE_420);
+
+  dt_lua_register_module_member(darktable.lua_state.state,
+                                self,
+                                dt_imageio_avif_t,
+                                subsample,
+                                enum avif_subsample_e);
 #endif
 }
 
@@ -250,17 +282,33 @@ int write_image(struct dt_imageio_module_data_t *data,
           format = AVIF_PIXEL_FORMAT_YUV444;
           break;
         case AVIF_COMP_LOSSY:
-          if(d->quality > 90)
+          // Determine pixel format based on subsample setting
+          switch(d->subsample)
           {
+            case AVIF_SUBSAMPLE_AUTO:
+              // Auto mode: use quality thresholds
+              if(d->quality > 90)
+              {
+                format = AVIF_PIXEL_FORMAT_YUV444;
+              }
+              else if(d->quality > 80)
+              {
+                format = AVIF_PIXEL_FORMAT_YUV422;
+              }
+              else
+              {
+                format = AVIF_PIXEL_FORMAT_YUV420;
+              }
+              break;
+            case AVIF_SUBSAMPLE_444:
               format = AVIF_PIXEL_FORMAT_YUV444;
-          }
-          else if(d->quality > 80)
-          {
+              break;
+            case AVIF_SUBSAMPLE_422:
               format = AVIF_PIXEL_FORMAT_YUV422;
-          }
-          else
-          {
-            format = AVIF_PIXEL_FORMAT_YUV420;
+              break;
+            case AVIF_SUBSAMPLE_420:
+              format = AVIF_PIXEL_FORMAT_YUV420;
+              break;
           }
           break;
       }
@@ -703,6 +751,7 @@ void *get_params(dt_imageio_module_format_t *self)
   }
 
   d->tiling = !dt_conf_get_bool("plugins/imageio/format/avif/tiling");
+  d->subsample = dt_conf_get_int("plugins/imageio/format/avif/subsample");
 
   return d;
 }
@@ -721,6 +770,7 @@ int set_params(dt_imageio_module_format_t *self,
   dt_bauhaus_combobox_set(g->tiling, d->tiling);
   dt_bauhaus_combobox_set(g->compression_type, d->compression_type);
   dt_bauhaus_slider_set(g->quality, d->quality);
+  dt_bauhaus_combobox_set(g->subsample, d->subsample);
 
   return 0;
 }
@@ -810,6 +860,7 @@ static void compression_type_changed(GtkWidget *widget, gpointer user_data)
   dt_conf_set_int("plugins/imageio/format/avif/compression_type", compression_type);
 
   gtk_widget_set_visible(gui->quality, compression_type != AVIF_COMP_LOSSLESS);
+  gtk_widget_set_visible(gui->subsample, compression_type != AVIF_COMP_LOSSLESS);
 }
 
 static void quality_changed(GtkWidget *slider, gpointer user_data)
@@ -818,6 +869,12 @@ static void quality_changed(GtkWidget *slider, gpointer user_data)
   dt_conf_set_int("plugins/imageio/format/avif/quality", quality);
 }
 
+static void subsample_changed(GtkWidget *widget, gpointer user_data)
+{
+  const enum avif_subsample_e subsample = dt_bauhaus_combobox_get(widget);
+  dt_conf_set_int("plugins/imageio/format/avif/subsample", subsample);
+}
+
 void gui_init(dt_imageio_module_format_t *self)
 {
   dt_imageio_avif_gui_t *gui = malloc(sizeof(dt_imageio_avif_gui_t));
@@ -904,17 +961,34 @@ void gui_init(dt_imageio_module_format_t *self)
   dt_bauhaus_widget_set_label(gui->quality,  NULL, N_("quality"));
 
   gtk_widget_set_tooltip_text(gui->quality,
-          _("the quality of an image, less quality means fewer details.\n"
-            "\n"
-            "pixel format is controlled by quality:\n"
-            "\n"
-            "5-80: YUV420, 81-90: YUV422, 91-100: YUV444"));
+          _("the quality of an image, less quality means fewer details"));
 
   dt_bauhaus_slider_set(gui->quality, quality);
 
   gtk_widget_set_visible(gui->quality, compression_type != AVIF_COMP_LOSSLESS);
   gtk_widget_set_no_show_all(gui->quality, TRUE);
 
+  /*
+   * Chroma subsampling combo box
+   */
+  const enum avif_subsample_e subsample = dt_conf_get_int("plugins/imageio/format/avif/subsample");
+
+  DT_BAUHAUS_COMBOBOX_NEW_FULL(gui->subsample, self, NULL, N_("chroma subsampling"),
+                               _("chroma subsampling setting for AVIF encoder.\n"
+                                 "auto - use subsampling determined by the quality value\n"
+                                 "      (5-80: YUV420, 81-90: YUV422, 91-100: YUV444)\n"
+                                 "4:4:4 - no chroma subsampling\n"
+                                 "4:2:2 - color sampling rate halved horizontally\n"
+                                 "4:2:0 - color sampling rate halved horizontally and vertically"),
+                               subsample, subsample_changed, self,
+                               N_("auto"), N_("4:4:4"), N_("4:2:2"), N_("4:2:0"));
+
+  dt_bauhaus_combobox_set_default(gui->subsample,
+                                  dt_confgen_get_int("plugins/imageio/format/avif/subsample", DT_DEFAULT));
+
+  gtk_widget_set_visible(gui->subsample, compression_type != AVIF_COMP_LOSSLESS);
+  gtk_widget_set_no_show_all(gui->subsample, TRUE);
+
   g_signal_connect(G_OBJECT(gui->bit_depth),
                    "value-changed",
                    G_CALLBACK(bit_depth_changed),
@@ -929,7 +1003,7 @@ void gui_init(dt_imageio_module_format_t *self)
                    NULL);
 
   self->widget = dt_gui_vbox(gui->bit_depth, gui->color_mode, gui->tiling,
-                             gui->compression_type, gui->quality);
+                             gui->compression_type, gui->quality, gui->subsample);
 }
 
 void gui_cleanup(dt_imageio_module_format_t *self)
@@ -946,6 +1020,7 @@ void gui_reset(dt_imageio_module_format_t *self)
   const enum avif_tiling_e tiling = !dt_confgen_get_bool("plugins/imageio/format/avif/tiling", DT_DEFAULT);
   const enum avif_compression_type_e compression_type = dt_confgen_get_int("plugins/imageio/format/avif/compression_type", DT_DEFAULT);
   const uint32_t quality = dt_confgen_get_int("plugins/imageio/format/avif/quality", DT_DEFAULT);
+  const enum avif_subsample_e subsample = dt_confgen_get_int("plugins/imageio/format/avif/subsample", DT_DEFAULT);
 
   size_t idx = 0;
   for(size_t i = 0; avif_bit_depth[i].name != NULL; ++i)
@@ -961,6 +1036,7 @@ void gui_reset(dt_imageio_module_format_t *self)
   dt_bauhaus_combobox_set(gui->tiling, tiling);
   dt_bauhaus_combobox_set(gui->compression_type, compression_type);
   dt_bauhaus_slider_set(gui->quality, quality);
+  dt_bauhaus_combobox_set(gui->subsample, subsample);
 }
 
 // clang-format off