print on mac os: fix double color management when using printer ICC profiles

src/common/cups_print.c

@@ -547,12 +547,36 @@ void dt_print_file(const dt_imgid_t imgid,
 
     cupsFreeDests(num_dests, dests);
 
-    // if we have a profile, disable cm on CUPS, this is important as dt does the cm
+    // When a printer ICC profile is selected, tell CUPS to skip its
+    // own color management — darktable already did the conversion
+    // via LittleCMS, and the ICC profile is embedded in the PDF.
+    //
+    // Linux: cm-calibration=true causes pdftoraster to set cm_disabled=1,
+    //        skipping its own color management.
+    //
+    // macOS: cgpdftoraster ignores cm-calibration. Instead we send
+    //        AP_ColorMatchingMode=AP_ApplicationColorMatching which
+    //        tells both cgpdftoraster and the printer driver that the
+    //        application already handled color matching.
 
     num_options = cupsAddOption("cm-calibration",
                                 *pinfo->printer.profile ? "true" : "false",
                                 num_options, &options);
 
+#ifdef __APPLE__
+    if(*pinfo->printer.profile)
+    {
+      // dot-notation variant appears to be legacy but is observed in
+      // print jobs from other macOS applications
+      num_options = cupsAddOption("AP.ColorMatchingMode",
+                                  "AP_ApplicationColorMatching",
+                                  num_options, &options);
+      num_options = cupsAddOption("AP_ColorMatchingMode",
+                                  "AP_ApplicationColorMatching",
+                                  num_options, &options);
+    }
+#endif
+
     // media to print on
 
     num_options = cupsAddOption("media", pinfo->paper.name, num_options, &options);

src/libs/print_settings.c

@@ -445,7 +445,7 @@ static void _create_pdf(dt_job_t *job,
 
   const float page_width  = dt_pdf_mm_to_point(width);
   const float page_height = dt_pdf_mm_to_point(height);
-  const int icc_id = 0;
+  int icc_id = 0;
 
   dt_pdf_image_t *pdf_image[MAX_IMAGE_PER_PAGE];
 
@@ -454,11 +454,19 @@ static void _create_pdf(dt_job_t *job,
                                params->prt.printer.resolution,
                                DT_PDF_STREAM_ENCODER_FLATE);
 
-/*
-  // ??? should a profile be embedded here?
-  if(*printer_profile)
-    icc_id = dt_pdf_add_icc(pdf, printer_profile);
-*/
+#ifdef __APPLE__
+  // On macOS, embed the printer ICC profile in the PDF so the
+  // already-converted pixel data is correctly tagged with its actual
+  // color space. Without this, cgpdftoraster assumes DeviceRGB = sRGB
+  // and misinterprets the data.
+  //
+  // On Linux this must NOT be done — Poppler (inside pdftoraster) would
+  // see the ICCBased color space and convert the data back to sRGB,
+  // undoing the LittleCMS conversion. Linux uses cm-calibration instead.
+  if(params->p_icc_profile && *params->p_icc_profile)
+    icc_id = dt_pdf_add_icc(pdf, params->p_icc_profile);
+#endif
+
   int32_t count = 0;
 
   for(int k=0; k<imgs.count; k++)
@@ -779,6 +787,13 @@ static void _print_button_clicked(GtkWidget *widget, dt_lib_module_t *self)
   params->p_icc_intent = ps->v_pintent;
   params->black_point_compensation = ps->v_black_point_compensation;
 
+  // Propagate the printer profile selection so dt_print_file() can
+  // tell CUPS to skip color management when dt already did the
+  // ICC conversion. See cups_print.c for platform-specific details.
+  if(ps->v_piccprofile && *ps->v_piccprofile)
+    g_strlcpy(params->prt.printer.profile, ps->v_piccprofile,
+              sizeof(params->prt.printer.profile));
+
   dt_control_add_job(DT_JOB_QUEUE_USER_EXPORT, job);
 }