Fix dual demosaicers

1. For xtrans sensors the high frequency content (via DT_IOP_DEMOSAIC_MARKESTEIJN_3) was not calculated and used at all!
2. The low frequency content calculation should only use the linear interpolation part of VNG4.
   This avoids artifacts introduced from the second phase of that algorithm.
   a) Most notably are dark pixels at sharp transitions on xtrans sensors, on bayer sensors this is a smaller issue.
   b) Under certain conditions there is a local color shift, especially on bayer yellow/brown tones.
3. Fix details threshold mask visualizing for CPU and in gui_changed() and make gui_update() using that.
4. Fixed OpenCL VNG code if only bilinear code was wanted.

We should better name the dual demosaicers not mentioning VNG as that is misleading but leave more info in the tooltips.
Use size_t instead of int where necessary for large images, some code simplifications.

Author: jenshannoschwalm

src/iop/demosaic.c

@@ -1,6 +1,6 @@
 /*
     This file is part of darktable,
-    Copyright (C) 2010-2024 darktable developers.
+    Copyright (C) 2010-2025 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
@@ -67,16 +67,16 @@ typedef enum dt_iop_demosaic_method_t
   DT_IOP_DEMOSAIC_VNG4 = 2,  // $DESCRIPTION: "VNG4"
   DT_IOP_DEMOSAIC_RCD = 5,   // $DESCRIPTION: "RCD"
   DT_IOP_DEMOSAIC_LMMSE = 6, // $DESCRIPTION: "LMMSE"
-  DT_IOP_DEMOSAIC_RCD_VNG = DT_DEMOSAIC_DUAL | DT_IOP_DEMOSAIC_RCD, // $DESCRIPTION: "RCD + VNG4"
-  DT_IOP_DEMOSAIC_AMAZE_VNG = DT_DEMOSAIC_DUAL | DT_IOP_DEMOSAIC_AMAZE, // $DESCRIPTION: "AMaZE + VNG4"
+  DT_IOP_DEMOSAIC_RCD_VNG = DT_DEMOSAIC_DUAL | DT_IOP_DEMOSAIC_RCD, // $DESCRIPTION: "RCD (dual)"
+  DT_IOP_DEMOSAIC_AMAZE_VNG = DT_DEMOSAIC_DUAL | DT_IOP_DEMOSAIC_AMAZE, // $DESCRIPTION: "AMaZE (dual)""
   DT_IOP_DEMOSAIC_PASSTHROUGH_MONOCHROME = 3, // $DESCRIPTION: "passthrough (monochrome)"
   DT_IOP_DEMOSAIC_PASSTHROUGH_COLOR = 4, // $DESCRIPTION: "photosite color (debug)"
   // methods for x-trans images
   DT_IOP_DEMOSAIC_VNG = DT_DEMOSAIC_XTRANS | 0,           // $DESCRIPTION: "VNG"
   DT_IOP_DEMOSAIC_MARKESTEIJN = DT_DEMOSAIC_XTRANS | 1,   // $DESCRIPTION: "Markesteijn 1-pass"
   DT_IOP_DEMOSAIC_MARKESTEIJN_3 = DT_DEMOSAIC_XTRANS | 2, // $DESCRIPTION: "Markesteijn 3-pass"
   DT_IOP_DEMOSAIC_FDC = DT_DEMOSAIC_XTRANS | 4,           // $DESCRIPTION: "frequency domain chroma"
-  DT_IOP_DEMOSAIC_MARKEST3_VNG = DT_DEMOSAIC_DUAL | DT_IOP_DEMOSAIC_MARKESTEIJN_3, // $DESCRIPTION: "Markesteijn 3-pass + VNG"
+  DT_IOP_DEMOSAIC_MARKEST3_VNG = DT_DEMOSAIC_DUAL | DT_IOP_DEMOSAIC_MARKESTEIJN_3, // $DESCRIPTION: "Markesteijn 3-pass (dual)"
   DT_IOP_DEMOSAIC_PASSTHR_MONOX = DT_DEMOSAIC_XTRANS | 3, // $DESCRIPTION: "passthrough (monochrome)"
   DT_IOP_DEMOSAIC_PASSTHR_COLORX = DT_DEMOSAIC_XTRANS | 5, // $DESCRIPTION: "photosite color (debug)"
 } dt_iop_demosaic_method_t;
@@ -585,40 +585,41 @@ void process(dt_iop_module_t *self,
              const dt_iop_roi_t *const roi_out)
 {
   const dt_image_t *img = &self->dev->image_storage;
+  dt_dev_pixelpipe_t *const pipe = piece->pipe;
 
-  dt_dev_clear_scharr_mask(piece->pipe);
+  dt_dev_clear_scharr_mask(pipe);
 
-  const gboolean run_fast = piece->pipe->type & DT_DEV_PIXELPIPE_FAST;
-  const gboolean fullpipe = piece->pipe->type & DT_DEV_PIXELPIPE_FULL;
+  const gboolean run_fast = pipe->type & DT_DEV_PIXELPIPE_FAST;
+  const gboolean fullpipe = pipe->type & DT_DEV_PIXELPIPE_FULL;
 
-  const uint8_t(*const xtrans)[6] = (const uint8_t(*const)[6])piece->pipe->dsc.xtrans;
+  const uint8_t(*const xtrans)[6] = (const uint8_t(*const)[6])pipe->dsc.xtrans;
 
   const dt_iop_demosaic_data_t *d = piece->data;
   const dt_iop_demosaic_gui_data_t *g = self->gui_data;
 
   const int qual_flags = demosaic_qual_flags(piece, img, roi_out);
   const gboolean fullscale = qual_flags & DT_DEMOSAIC_FULL_SCALE;
-  const gboolean is_xtrans = piece->pipe->dsc.filters == 9u;
+  const gboolean is_xtrans = pipe->dsc.filters == 9u;
   const gboolean is_4bayer = img->flags & DT_IMAGE_4BAYER;
-  const gboolean is_bayer = !is_xtrans && piece->pipe->dsc.filters != 0;
+  const gboolean is_bayer = !is_xtrans && pipe->dsc.filters != 0;
 
   int demosaicing_method = d->demosaicing_method;
   const int width = roi_in->width;
   const int height = roi_in->height;
 
   if(width < 16 || height < 16)
-    demosaicing_method = is_xtrans ? DT_IOP_DEMOSAIC_MARKEST3_VNG : DT_IOP_DEMOSAIC_VNG4;
+    demosaicing_method = is_xtrans ? DT_IOP_DEMOSAIC_VNG : DT_IOP_DEMOSAIC_VNG4;
 
   gboolean showmask = FALSE;
   if(self->dev->gui_attached && fullpipe)
   {
     if(g->visual_mask)
     {
       showmask = TRUE;
-      piece->pipe->mask_display = DT_DEV_PIXELPIPE_DISPLAY_MASK;
+      pipe->mask_display = DT_DEV_PIXELPIPE_DISPLAY_MASK;
     }
     // take care of passthru modes
-    if(piece->pipe->mask_display == DT_DEV_PIXELPIPE_DISPLAY_PASSTHRU)
+    if(pipe->mask_display == DT_DEV_PIXELPIPE_DISPLAY_PASSTHRU)
       demosaicing_method = is_xtrans ? DT_IOP_DEMOSAIC_MARKESTEIJN : DT_IOP_DEMOSAIC_RCD;
   }
 
@@ -627,13 +628,13 @@ void process(dt_iop_module_t *self,
 
   if(!fullscale)
   {
-    dt_print_pipe(DT_DEBUG_PIPE, "demosaic approx zoom", piece->pipe, self, DT_DEVICE_CPU, roi_in, roi_out);
+    dt_print_pipe(DT_DEBUG_PIPE, "demosaic approx zoom", pipe, self, DT_DEVICE_CPU, roi_in, roi_out);
     if(demosaicing_method == DT_IOP_DEMOSAIC_PASSTHROUGH_MONOCHROME || demosaicing_method == DT_IOP_DEMOSAIC_PASSTHROUGH_COLOR)
       dt_iop_clip_and_zoom_demosaic_passthrough_monochrome_f(out, in, roi_out, roi_in, roi_out->width, width);
     else if(is_xtrans)
       dt_iop_clip_and_zoom_demosaic_third_size_xtrans_f(out, in, roi_out, roi_in, roi_out->width, width, xtrans);
     else
-      dt_iop_clip_and_zoom_demosaic_half_size_f(out, in, roi_out, roi_in, roi_out->width, width, piece->pipe->dsc.filters);
+      dt_iop_clip_and_zoom_demosaic_half_size_f(out, in, roi_out, roi_in, roi_out->width, width, pipe->dsc.filters);
 
     return;
   }
@@ -655,15 +656,15 @@ void process(dt_iop_module_t *self,
     switch(d->green_eq)
     {
       case DT_IOP_GREEN_EQ_FULL:
-        green_equilibration_favg(in, (float *)i, width, height, piece->pipe->dsc.filters, roi_in->x, roi_in->y);
+        green_equilibration_favg(in, (float *)i, width, height, pipe->dsc.filters, roi_in->x, roi_in->y);
         break;
       case DT_IOP_GREEN_EQ_LOCAL:
-        green_equilibration_lavg(in, (float *)i, width, height, piece->pipe->dsc.filters, roi_in->x, roi_in->y, threshold);
+        green_equilibration_lavg(in, (float *)i, width, height, pipe->dsc.filters, roi_in->x, roi_in->y, threshold);
         break;
       case DT_IOP_GREEN_EQ_BOTH:
         aux = dt_alloc_align_float((size_t)height * width);
-        green_equilibration_favg(aux, (float *)i, width, height, piece->pipe->dsc.filters, roi_in->x, roi_in->y);
-        green_equilibration_lavg(in, aux, width, height, piece->pipe->dsc.filters, roi_in->x, roi_in->y, threshold);
+        green_equilibration_favg(aux, (float *)i, width, height, pipe->dsc.filters, roi_in->x, roi_in->y);
+        green_equilibration_lavg(in, aux, width, height, pipe->dsc.filters, roi_in->x, roi_in->y, threshold);
         dt_free_align(aux);
         break;
       default:
@@ -674,52 +675,50 @@ void process(dt_iop_module_t *self,
   if(demosaicing_method == DT_IOP_DEMOSAIC_PASSTHROUGH_MONOCHROME)
     passthrough_monochrome(out, in, roi_in);
   else if(demosaicing_method == DT_IOP_DEMOSAIC_PASSTHROUGH_COLOR)
-    passthrough_color(out, in, roi_in, piece->pipe->dsc.filters, xtrans);
+    passthrough_color(out, in, roi_in, pipe->dsc.filters, xtrans);
   else if(is_xtrans)
   {
     const int passes = base_demosaicing_method == DT_IOP_DEMOSAIC_MARKESTEIJN_3 ? 3 : 1;
-    if(demosaicing_method == DT_IOP_DEMOSAIC_MARKEST3_VNG)
-      vng_interpolate(out, in, roi_in, piece->pipe->dsc.filters, xtrans, qual_flags & DT_DEMOSAIC_ONLY_VNG_LINEAR);
-    else if(demosaicing_method == DT_IOP_DEMOSAIC_FDC)
+    if(demosaicing_method == DT_IOP_DEMOSAIC_FDC)
       xtrans_fdc_interpolate(self, out, in, roi_in, xtrans);
     else if(base_demosaicing_method == DT_IOP_DEMOSAIC_MARKESTEIJN || base_demosaicing_method == DT_IOP_DEMOSAIC_MARKESTEIJN_3)
       xtrans_markesteijn_interpolate(out, in, roi_in, xtrans, passes);
     else
-      vng_interpolate(out, in, roi_in, piece->pipe->dsc.filters, xtrans, qual_flags & DT_DEMOSAIC_ONLY_VNG_LINEAR);
+      vng_interpolate(out, in, roi_in, pipe->dsc.filters, xtrans, qual_flags & DT_DEMOSAIC_ONLY_VNG_LINEAR);
   }
   else
   {
     if(demosaicing_method == DT_IOP_DEMOSAIC_VNG4 || is_4bayer)
     {
-      vng_interpolate(out, in, roi_in, piece->pipe->dsc.filters, xtrans, qual_flags & DT_DEMOSAIC_ONLY_VNG_LINEAR);
+      vng_interpolate(out, in, roi_in, pipe->dsc.filters, xtrans, qual_flags & DT_DEMOSAIC_ONLY_VNG_LINEAR);
       if(is_4bayer)
       {
         dt_colorspaces_cygm_to_rgb(out, width * height, d->CAM_to_RGB);
-        dt_colorspaces_cygm_to_rgb(piece->pipe->dsc.processed_maximum, 1, d->CAM_to_RGB);
+        dt_colorspaces_cygm_to_rgb(pipe->dsc.processed_maximum, 1, d->CAM_to_RGB);
       }
     }
     else if(base_demosaicing_method == DT_IOP_DEMOSAIC_RCD)
-      rcd_demosaic(piece, out, in, roi_in, piece->pipe->dsc.filters);
+      rcd_demosaic(piece, out, in, roi_in, pipe->dsc.filters);
     else if(demosaicing_method == DT_IOP_DEMOSAIC_LMMSE)
-      lmmse_demosaic(piece, out, in, roi_in, piece->pipe->dsc.filters, d->lmmse_refine);
+      lmmse_demosaic(piece, out, in, roi_in, pipe->dsc.filters, d->lmmse_refine);
     else if(base_demosaicing_method != DT_IOP_DEMOSAIC_AMAZE)
-      demosaic_ppg(out, in, roi_in, piece->pipe->dsc.filters, d->median_thrs);
+      demosaic_ppg(out, in, roi_in, pipe->dsc.filters, d->median_thrs);
     else
-      amaze_demosaic(piece, in, out, roi_in, piece->pipe->dsc.filters);
+      amaze_demosaic(piece, in, out, roi_in, pipe->dsc.filters);
   }
 
-  if(piece->pipe->want_detail_mask)
+  if(pipe->want_detail_mask)
     dt_dev_write_scharr_mask(piece, out, roi_in, TRUE);
 
   if(dual)
-    dual_demosaic(piece, out, in, roi_in, piece->pipe->dsc.filters, xtrans, showmask, d->dual_thrs);
+    dual_demosaic(piece, out, in, roi_in, pipe->dsc.filters, xtrans, showmask, d->dual_thrs);
 
   if((float *)i != in) dt_free_align(in);
 
   if(d->color_smoothing)
     color_smoothing(out, roi_in, d->color_smoothing);
 
-  dt_print_pipe(DT_DEBUG_PIPE, direct ? "demosaic inplace" : "demosaic clip_and_zoom", piece->pipe, self, DT_DEVICE_CPU, roi_in, roi_out);
+  dt_print_pipe(DT_DEBUG_PIPE, direct ? "demosaic inplace" : "demosaic clip_and_zoom", pipe, self, DT_DEVICE_CPU, roi_in, roi_out);
   if(!direct)
   {
     dt_iop_roi_t roo = *roi_out;
@@ -740,14 +739,15 @@ int process_cl(dt_iop_module_t *self,
                const dt_iop_roi_t *const roi_out)
 {
   const dt_image_t *img = &self->dev->image_storage;
-  const gboolean run_fast = piece->pipe->type & DT_DEV_PIXELPIPE_FAST;
-  const gboolean fullpipe = piece->pipe->type & DT_DEV_PIXELPIPE_FULL;
+  dt_dev_pixelpipe_t *const pipe = piece->pipe;
+  const gboolean run_fast = pipe->type & DT_DEV_PIXELPIPE_FAST;
+  const gboolean fullpipe = pipe->type & DT_DEV_PIXELPIPE_FULL;
   const int qual_flags = demosaic_qual_flags(piece, img, roi_out);
   const gboolean fullscale = qual_flags & DT_DEMOSAIC_FULL_SCALE;
-  const gboolean is_xtrans = piece->pipe->dsc.filters == 9u;
-  const gboolean is_bayer = !is_xtrans && piece->pipe->dsc.filters != 0;
+  const gboolean is_xtrans = pipe->dsc.filters == 9u;
+  const gboolean is_bayer = !is_xtrans && pipe->dsc.filters != 0;
 
-  dt_dev_clear_scharr_mask(piece->pipe);
+  dt_dev_clear_scharr_mask(pipe);
 
   const dt_iop_demosaic_data_t *d = piece->data;
   const dt_iop_demosaic_gui_data_t *g = self->gui_data;
@@ -758,41 +758,41 @@ int process_cl(dt_iop_module_t *self,
   // We do a PPG to RCD demosaicer fallback here as the used driver is known to fail.
   // Also could "return DT_OPENCL_DT_EXCEPTION" for a cpu fallback
   if(demosaicing_method == DT_IOP_DEMOSAIC_PPG
-     && dt_opencl_exception(piece->pipe->devid, DT_OPENCL_AMD_APP))
+     && dt_opencl_exception(pipe->devid, DT_OPENCL_AMD_APP))
     demosaicing_method = DT_IOP_DEMOSAIC_RCD;
 
   const int width = roi_in->width;
   const int height = roi_in->height;
 
   if(width < 16 || height < 16)
-    demosaicing_method = is_xtrans ? DT_IOP_DEMOSAIC_MARKEST3_VNG : DT_IOP_DEMOSAIC_VNG4;
+    demosaicing_method = is_xtrans ? DT_IOP_DEMOSAIC_VNG : DT_IOP_DEMOSAIC_VNG4;
 
   gboolean showmask = FALSE;
   if(self->dev->gui_attached && fullpipe)
   {
     if(g->visual_mask)
     {
       showmask = TRUE;
-      piece->pipe->mask_display = DT_DEV_PIXELPIPE_DISPLAY_MASK;
+      pipe->mask_display = DT_DEV_PIXELPIPE_DISPLAY_MASK;
     }
     // take care of passthru modes
-    if(piece->pipe->mask_display == DT_DEV_PIXELPIPE_DISPLAY_PASSTHRU)
+    if(pipe->mask_display == DT_DEV_PIXELPIPE_DISPLAY_PASSTHRU)
       demosaicing_method = is_xtrans ? DT_IOP_DEMOSAIC_MARKESTEIJN : DT_IOP_DEMOSAIC_RCD;
   }
 
-  const int devid = piece->pipe->devid;
+  const int devid = pipe->devid;
 
   cl_int err = CL_MEM_OBJECT_ALLOCATION_FAILURE;
 
   if(dev_in  == NULL || dev_out == NULL) return err;
 
   if(!fullscale)
   {
-    dt_print_pipe(DT_DEBUG_PIPE, "demosaic approx zoom", piece->pipe, self, piece->pipe->devid, roi_in, roi_out);
+    dt_print_pipe(DT_DEBUG_PIPE, "demosaic approx zoom", pipe, self, devid, roi_in, roi_out);
     const int zero = 0;
     if(is_xtrans)
     {
-      cl_mem dev_xtrans = dt_opencl_copy_host_to_device_constant(devid, sizeof(piece->pipe->dsc.xtrans), piece->pipe->dsc.xtrans);
+      cl_mem dev_xtrans = dt_opencl_copy_host_to_device_constant(devid, sizeof(pipe->dsc.xtrans), pipe->dsc.xtrans);
       if(dev_xtrans == NULL) return err;
       // sample third-size image
       err = dt_opencl_enqueue_kernel_2d_args(devid, gd->kernel_zoom_third_size, roi_out->width, roi_out->height,
@@ -804,11 +804,11 @@ int process_cl(dt_iop_module_t *self,
     else if(demosaicing_method == DT_IOP_DEMOSAIC_PASSTHROUGH_MONOCHROME)
       return dt_opencl_enqueue_kernel_2d_args(devid, gd->kernel_zoom_passthrough_monochrome, roi_out->width, roi_out->height,
           CLARG(dev_in), CLARG(dev_out), CLARG(roi_out->width), CLARG(roi_out->height), CLARG(zero), CLARG(zero), CLARG(width),
-          CLARG(height), CLARG(roi_out->scale), CLARG(piece->pipe->dsc.filters));
+          CLARG(height), CLARG(roi_out->scale), CLARG(pipe->dsc.filters));
     else // bayer
       return dt_opencl_enqueue_kernel_2d_args(devid, gd->kernel_zoom_half_size, roi_out->width, roi_out->height,
           CLARG(dev_in), CLARG(dev_out), CLARG(roi_out->width), CLARG(roi_out->height), CLARG(zero), CLARG(zero), CLARG(width),
-          CLARG(height), CLARG(roi_out->scale), CLARG(piece->pipe->dsc.filters));
+          CLARG(height), CLARG(roi_out->scale), CLARG(pipe->dsc.filters));
   }
 
   const gboolean direct = roi_out->width == width && roi_out->height == height && feqf(roi_in->scale, roi_out->scale, 1e-8f);
@@ -847,24 +847,19 @@ int process_cl(dt_iop_module_t *self,
     err = process_vng_cl(self, piece, in_image, out_image, roi_in, FALSE);
     if(err != CL_SUCCESS) goto finish;
   }
-  else if(demosaicing_method == DT_IOP_DEMOSAIC_MARKEST3_VNG)
-  {
-    err = process_vng_cl(self, piece, in_image, out_image, roi_in, qual_flags & DT_DEMOSAIC_ONLY_VNG_LINEAR);
-    if(err != CL_SUCCESS) goto finish;
-  }
   else if(base_demosaicing_method == DT_IOP_DEMOSAIC_MARKESTEIJN || base_demosaicing_method == DT_IOP_DEMOSAIC_MARKESTEIJN_3)
   {
     err = process_markesteijn_cl(self, piece, in_image, out_image, roi_in);
     if(err != CL_SUCCESS) goto finish;
   }
   else
   {
-    dt_print(DT_DEBUG_OPENCL, "[opencl_demosaic] demosaicing method %d not yet supported by opencl code", demosaicing_method);
+    dt_print(DT_DEBUG_ALWAYS, "[opencl_demosaic] demosaicing method %d not yet supported by opencl code", demosaicing_method);
     err = DT_OPENCL_PROCESS_CL;
     goto finish;
   }
 
-  if(piece->pipe->want_detail_mask)
+  if(pipe->want_detail_mask)
   {
     err = dt_dev_write_scharr_mask_cl(piece, out_image, roi_in, TRUE);
     if(err != CL_SUCCESS) goto finish;
@@ -881,7 +876,7 @@ int process_cl(dt_iop_module_t *self,
       size_t region[] = { width, height, 1 };
       err = dt_opencl_enqueue_copy_image(devid, out_image, cp_image, origin, origin, region);
       if(err == CL_SUCCESS)
-        err = process_vng_cl(self, piece, in_image, low_image, roi_in, FALSE);
+        err = process_vng_cl(self, piece, in_image, low_image, roi_in, TRUE);
       if(err == CL_SUCCESS)
         err = color_smoothing_cl(self, piece, low_image, low_image, roi_in, DT_DEMOSAIC_SMOOTH_2);
       if(err == CL_SUCCESS)
@@ -904,7 +899,7 @@ int process_cl(dt_iop_module_t *self,
     if(err != CL_SUCCESS) goto finish;
   }
 
-  dt_print_pipe(DT_DEBUG_PIPE, direct ? "demosaic inplace" : "demosaic clip_and_zoom", piece->pipe, self, piece->pipe->devid, roi_in, roi_out);
+  dt_print_pipe(DT_DEBUG_PIPE, direct ? "demosaic inplace" : "demosaic clip_and_zoom", pipe, self, devid, roi_in, roi_out);
   if(!direct)
     err = dt_iop_clip_and_zoom_roi_cl(devid, dev_out, out_image, roi_out, roi_in);
 
@@ -1271,19 +1266,20 @@ void gui_changed(dt_iop_module_t *self, GtkWidget *w, void *previous)
     dt_dev_reload_image(self->dev, self->dev->image_storage.id);
   }
 
+  if(!w || w != g->dual_thrs)
+  {
+    dt_bauhaus_widget_set_quad_active(g->dual_thrs, FALSE);
+    g->visual_mask = FALSE;
+  }
+
   // as the dual modes change behaviour for previous pipeline modules we do a reprocess
   if(isdual && (w == g->demosaic_method_bayer || w == g->demosaic_method_xtrans))
     dt_dev_reprocess_center(self->dev);
 }
 
 void gui_update(dt_iop_module_t *self)
 {
-  dt_iop_demosaic_gui_data_t *g = self->gui_data;
-  dt_bauhaus_widget_set_quad_active(g->dual_thrs, FALSE);
-
-  g->visual_mask = FALSE;
   gui_changed(self, NULL, NULL);
-
   gtk_stack_set_visible_child_name(GTK_STACK(self->widget), self->default_enabled ? "raw" : "non_raw");
 }
 
@@ -1319,11 +1315,11 @@ void gui_init(dt_iop_module_t *self)
   const int xtranspos = dt_bauhaus_combobox_get_from_value(g->demosaic_method_bayer, DT_DEMOSAIC_XTRANS);
 
   for(int i=0;i<7;i++) dt_bauhaus_combobox_remove_at(g->demosaic_method_bayer, xtranspos);
-  gtk_widget_set_tooltip_text(g->demosaic_method_bayer, _("Bayer sensor demosaicing method, PPG and RCD are fast, AMaZE and LMMSE are slow.\nLMMSE is suited best for high ISO images.\ndual demosaicers double processing time."));
+  gtk_widget_set_tooltip_text(g->demosaic_method_bayer, _("Bayer sensor demosaicing method, PPG and RCD are fast, AMaZE and LMMSE are slow.\nLMMSE is suited best for high ISO images.\ndual demosaicers increase processing time by blending a VNG variant in a second pass."));
 
   g->demosaic_method_xtrans = dt_bauhaus_combobox_from_params(self, "demosaicing_method");
   for(int i=0;i<xtranspos;i++) dt_bauhaus_combobox_remove_at(g->demosaic_method_xtrans, 0);
-  gtk_widget_set_tooltip_text(g->demosaic_method_xtrans, _("X-Trans sensor demosaicing method, Markesteijn 3-pass and frequency domain chroma are slow.\ndual demosaicers double processing time."));
+  gtk_widget_set_tooltip_text(g->demosaic_method_xtrans, _("X-Trans sensor demosaicing method, Markesteijn 3-pass and frequency domain chroma are slow.\ndual demosaicers increase processing time by blending a VNG variant in a second pass."));
 
   g->demosaic_method_bayerfour = dt_bauhaus_combobox_from_params(self, "demosaicing_method");
   for(int i=0;i<7;i++) dt_bauhaus_combobox_remove_at(g->demosaic_method_bayerfour, xtranspos);