agx, sigmoid: follow the output's peak for HDR export

RELEASE_NOTES.md

@@ -230,6 +230,17 @@ changes (where available).
 
 ## Other Changes
 
+- AgX and sigmoid now adapt to HDR output, so one edit exports to
+  SDR, HLG and PQ alike. HLG output peaks at 1000 nits, and PQ output
+  at the new "PQ peak" setting of the export module, 1000 nits by
+  default, which export presets store and darktable-cli sets with
+  `--pq-peak`. With AgX, shadows and midtones keep their SDR brightness
+  and highlights extend to the peak, following Blender's AgX HDR, with
+  a new "HDR purity" slider for the highlights' saturation. Sigmoid
+  scales its target white to the peak, up to 1600% (3248 nits). SDR
+  output is unchanged. Existing edits render as before, and a "follow
+  output peak" toggle in each module opts them in.
+
 - PNG exports using a PQ output color profile now include content
   light level metadata (MaxCLL and MaxFALL) for HDR tone mapping.
 
@@ -360,6 +371,9 @@ changes (where available).
   opened: going back in the history showed masks from before the step
   that added them.
 
+- Fixed AgX rendering everything above the pivot black when pivot
+  target output was 100% and shoulder power was 7 or more.
+
 - Fixed shift-click on the selected entry of the history stack, which
   did nothing instead of revealing that module in the right-hand panel.
 

data/darktableconfig.xml.in

@@ -2684,6 +2684,13 @@
     <shortdescription>always use LittleCMS 2 to apply output color profile</shortdescription>
     <longdescription>this is slower than the default.</longdescription>
   </dtconfig>
+  <dtconfig>
+    <name>plugins/lighttable/export/pq_peak_nits</name>
+    <type min="203" max="10000">int</type>
+    <default>1000</default>
+    <shortdescription>PQ peak luminance</shortdescription>
+    <longdescription>the brightest highlight a PQ (HDR) output should reach, in nits. tone mappers that follow the output map their white to this peak. HLG output always peaks at 1000 nits and SDR output at the 203 nit reference white.</longdescription>
+  </dtconfig>
   <dtconfig>
     <name>plugins/lighttable/export/high_quality_processing</name>
     <type>bool</type>

data/kernels/agx.cl

@@ -21,6 +21,19 @@
 
 #define _epsilon 1E-6f
 
+// Must match hdr_params_t in C code
+typedef struct dt_iop_agx_hdr_params_t
+{
+  int enabled;
+  float headroom;
+  float purity;
+  float log_min;
+  float pivot_x;
+  float pivot_y;
+  float toe_scale;
+  float shoulder_scale;
+} dt_iop_agx_hdr_params_t;
+
 // Must match tone_mapping_params_t in C code
 typedef struct dt_iop_agx_tone_mapping_params_t
 {
@@ -55,6 +68,7 @@ typedef struct dt_iop_agx_tone_mapping_params_t
   float look_original_hue_mix_ratio;
   int look_tuned;
   int restore_hue;
+  dt_iop_agx_hdr_params_t hdr;
 } dt_iop_agx_tone_mapping_params_t;
 
 static inline void _agx_compress_into_gamut(float4 *pixel)
@@ -175,6 +189,36 @@ static inline float _agx_lerp_hue(const float original_hue, const float processe
     return mixed_hue - floor(mixed_hue);
 }
 
+// see _hdr_darken() in agx.c
+static inline float _agx_hdr_darken(const float x, const dt_iop_agx_hdr_params_t *hdr)
+{
+    const float log_x = clamp(1.0f - dtcl_log2(fmax(x, 1e-12f)) / hdr->log_min, 0.0f, 1.0f);
+    const float u = log_x - hdr->pivot_x;
+    const float log_y = u < 0.0f
+        ? _agx_scaled_sigmoid(log_x, hdr->toe_scale, 1.0f, 3.0f, hdr->pivot_x, hdr->pivot_y)
+        : hdr->pivot_y + hdr->shoulder_scale * u / (hdr->shoulder_scale + u);
+    return x > 0.0f ? dtcl_exp2(hdr->log_min * (1.0f - log_y)) : 0.0f;
+}
+
+// see _agx_hdr() in agx.c
+static inline void _agx_hdr(float4 *pixel, const dt_iop_agx_hdr_params_t *hdr)
+{
+    const float4 hsv_before = RGB_2_HSV(*pixel);
+    float4 darkened = *pixel;
+    darkened.x = _agx_hdr_darken(pixel->x, hdr);
+    darkened.y = _agx_hdr_darken(pixel->y, hdr);
+    darkened.z = _agx_hdr_darken(pixel->z, hdr);
+    float4 hsv_after = RGB_2_HSV(darkened);
+
+    hsv_after.x = _agx_lerp_hue(hsv_before.x, hsv_after.x, 1.0f - hdr->purity);
+    hsv_after.y = hsv_before.y + hdr->purity * (hsv_after.y - hsv_before.y);
+    darkened = HSV_2_RGB(hsv_after);
+
+    pixel->x = hdr->headroom * darkened.x;
+    pixel->y = hdr->headroom * darkened.y;
+    pixel->z = hdr->headroom * darkened.z;
+}
+
 static inline void _agx_tone_mapping(float4 *rgb_in_out, const dt_iop_agx_tone_mapping_params_t *params, constant float *rendering_to_xyz)
 {
     float4 hsv_pixel = (float4)(0.0f, 0.0f, 0.0f, 0.0f);
@@ -199,6 +243,11 @@ static inline void _agx_tone_mapping(float4 *rgb_in_out, const dt_iop_agx_tone_m
     transformed_pixel.y = dtcl_pow(fmax(0.0f, transformed_pixel.y), params->curve_gamma);
     transformed_pixel.z = dtcl_pow(fmax(0.0f, transformed_pixel.z), params->curve_gamma);
 
+    if(params->hdr.enabled)
+    {
+        _agx_hdr(&transformed_pixel, &params->hdr);
+    }
+
     if(params->restore_hue)
     {
         hsv_pixel = RGB_2_HSV(transformed_pixel);

src/cli/main.c

@@ -34,6 +34,7 @@
 #include "common/history.h"
 #include "common/image.h"
 #include "common/image_cache.h"
+#include "common/iop_profile.h"
 #include "common/points.h"
 #include "control/conf.h"
 #include "develop/imageop.h"
@@ -102,6 +103,8 @@ fprintf(stderr, "darktable %s\n"
                 "   --icc-file <file> specify icc filename, default to NONE\n"
                 "   --icc-intent <intent> specify icc intent, default to LAST\n"
                 "                     use --help icc-intent for list of supported intents\n"
+                "   --pq-peak <nits>  peak luminance of PQ output, 203 to 10000,\n"
+                "                     default from the export module's setting\n"
                 "   --print-paths     print the resolved configdir, cachedir, tmpdir,\n"
                 "                     datadir, moduledir, localedir and library paths\n"
                 "                     for this install, then exit\n"
@@ -250,6 +253,7 @@ int main(int argc, char *arg[])
   dt_colorspaces_color_profile_type_t icc_type = DT_COLORSPACE_NONE;
   gchar *icc_filename = NULL;
   dt_iop_color_intent_t icc_intent = DT_INTENT_LAST;
+  int pq_peak_nits = 0;
 
   int k;
   for(k = 1; k < argc; k++)
@@ -438,6 +442,17 @@ int main(int argc, char *arg[])
           exit(1);
         }
       }
+      else if(!strcmp(arg[k], "--pq-peak") && argc > k + 1)
+      {
+        k++;
+        pq_peak_nits = atoi(arg[k]);
+        if(pq_peak_nits < DT_HDR_REFERENCE_WHITE_NITS || pq_peak_nits > 10000)
+        {
+          fprintf(stderr, _("incorrect PQ peak for --pq-peak: '%s'\n"), arg[k]);
+          usage(arg[0]);
+          exit(1);
+        }
+      }
       else if(!strcmp(arg[k], "-v") || !strcmp(arg[k], "--verbose"))
       {
         verbose = TRUE;
@@ -880,6 +895,9 @@ int main(int argc, char *arg[])
 
   // TODO: add a callback to set the bpp without going through the config
 
+  // the exports below run in this thread
+  dt_ioppr_set_thread_pq_peak_nits(pq_peak_nits);
+
   int num = 1, res = 0;
   for(GList *iter = id_list; iter; iter = g_list_next(iter), num++)
   {

src/common/iop_profile.c

@@ -806,6 +806,35 @@ dt_ioppr_set_pipe_input_profile_info(struct dt_develop_t *dev,
   return profile_info;
 }
 
+// per thread, so that an export job keeps the peak it was started with
+// without writing the setting shared with the export module and the darkroom
+static __thread int _thread_pq_peak_nits = 0;
+
+void dt_ioppr_set_thread_pq_peak_nits(const int nits)
+{
+  _thread_pq_peak_nits = nits;
+}
+
+static float _output_headroom(const dt_colorspaces_color_profile_type_t type)
+{
+  switch(dt_colorspaces_hdr_transfer(type))
+  {
+    case DT_HDR_PQ:
+    {
+      const int nits = _thread_pq_peak_nits > 0
+        ? _thread_pq_peak_nits
+        : dt_conf_get_int("plugins/lighttable/export/pq_peak_nits");
+      return fmaxf(1.0f, nits / DT_HDR_REFERENCE_WHITE_NITS);
+    }
+    case DT_HDR_HLG_REC2020:
+    case DT_HDR_HLG_P3:
+      // colorout's OOTF clips HLG at the nominal 1000 nit display
+      return DT_HDR_HLG_PEAK_NITS / DT_HDR_REFERENCE_WHITE_NITS;
+    default:
+      return 1.0f;
+  }
+}
+
 dt_iop_order_iccprofile_info_t *
 dt_ioppr_set_pipe_output_profile_info(struct dt_develop_t *dev,
                                       struct dt_dev_pixelpipe_t *pipe,
@@ -834,6 +863,7 @@ dt_ioppr_set_pipe_output_profile_info(struct dt_develop_t *dev,
     profile_info = dt_ioppr_add_profile_info_to_list(dev, DT_COLORSPACE_SRGB, "", intent);
   }
   pipe->output_profile_info = profile_info;
+  pipe->output_headroom = _output_headroom(profile_info->type);
 
   return profile_info;
 }

src/common/iop_profile.h

@@ -116,6 +116,10 @@ dt_ioppr_set_pipe_output_profile_info(struct dt_develop_t *dev,
                                       const char *filename,
                                       const int intent);
 
+/** set the PQ peak, in nits, for the pipes processed by the calling thread,
+   or 0 to read it from the export module's setting again */
+void dt_ioppr_set_thread_pq_peak_nits(const int nits);
+
 /** Record the export profile, used as a cache-identity tag. Returns the (possibly NULL)
    interned profile-info pointer, no fallback for sRGB in case of failure. */
 dt_iop_order_iccprofile_info_t *

src/control/jobs/control_jobs.c

@@ -105,6 +105,7 @@ typedef struct dt_control_export_t
   dt_colorspaces_color_profile_type_t icc_type;
   gchar *icc_filename;
   dt_iop_color_intent_t icc_intent;
+  int pq_peak_nits;
   gchar *metadata_export;
 } dt_control_export_t;
 
@@ -2096,6 +2097,9 @@ static int32_t _control_export_job_run(dt_job_t *job)
   GList *t = params->index;
   double prev_time = 0;
 
+  // the peak set when the export was queued, not the setting's current value
+  dt_ioppr_set_thread_pq_peak_nits(settings->pq_peak_nits);
+
   while(t && !_job_cancelled(job))
   {
     const dt_imgid_t imgid = GPOINTER_TO_INT(t->data);
@@ -2148,6 +2152,7 @@ static int32_t _control_export_job_run(dt_job_t *job)
     fraction += 1.0 / total;
     _update_progress(job, fraction, &prev_time);
   }
+  dt_ioppr_set_thread_pq_peak_nits(0);
   g_list_free_full(metadata.list, g_free);
 
   if(mstorage->finalize_store) mstorage->finalize_store(mstorage, sdata);
@@ -2747,6 +2752,7 @@ void dt_control_export(GList *imgid_list,
                        const dt_colorspaces_color_profile_type_t icc_type,
                        const gchar *icc_filename,
                        const dt_iop_color_intent_t icc_intent,
+                       const int pq_peak_nits,
                        const gchar *metadata_export)
 {
   dt_job_t *job = dt_control_job_create(&_control_export_job_run, "export");
@@ -2803,6 +2809,7 @@ void dt_control_export(GList *imgid_list,
   data->icc_type = icc_type;
   data->icc_filename = g_strdup(icc_filename);
   data->icc_intent = icc_intent;
+  data->pq_peak_nits = pq_peak_nits;
   data->metadata_export = g_strdup(metadata_export);
 
   dt_control_job_add_progress(job, _("export images"), TRUE);

src/control/jobs/control_jobs.h

@@ -64,6 +64,7 @@ void dt_control_export(GList *imgid_list,
                        const dt_colorspaces_color_profile_type_t icc_type,
                        const gchar *icc_filename,
                        const dt_iop_color_intent_t icc_intent,
+                       const int pq_peak_nits,
                        const gchar *metadata_export);
 void dt_control_merge_hdr(void);
 void dt_control_import(GList *imgs, const char *datetime_override, const gboolean inplace);

src/develop/pixelpipe_cache.c

@@ -122,6 +122,8 @@ static dt_hash_t _dev_pixelpipe_cache_basichash(dt_dev_pixelpipe_t *pipe,
   hash = dt_hash(hash, &pipe->work_profile_info, sizeof(pipe->work_profile_info));
   hash = dt_hash(hash, &pipe->output_profile_info, sizeof(pipe->output_profile_info));
   hash = dt_hash(hash, &pipe->export_profile_info, sizeof(pipe->export_profile_info));
+  // the PQ peak is a preference, so the output profile alone does not fix the headroom
+  hash = dt_hash(hash, &pipe->output_headroom, sizeof(pipe->output_headroom));
 
   // go through all modules up to position and compute a hash using the operation and params.
   GList *pieces = pipe->nodes;

src/develop/pixelpipe_hb.c

@@ -318,6 +318,7 @@ static gboolean _dev_pixelpipe_init_cached(dt_dev_pixelpipe_t *pipe,
   pipe->input_profile_info = NULL;
   pipe->output_profile_info = NULL;
   pipe->export_profile_info = NULL;
+  pipe->output_headroom = 1.0f;
   pipe->runs = 0;
   pipe->bcache_data = NULL;
   pipe->bcache_size = 0;

src/develop/pixelpipe_hb.h

@@ -237,6 +237,9 @@ typedef struct dt_dev_pixelpipe_t
   struct dt_iop_order_iccprofile_info_t *output_profile_info;
   /** used only as a cache-identity tag to invalidate the cache **/
   struct dt_iop_order_iccprofile_info_t *export_profile_info;
+  /** peak luminance of the output relative to the 203 nit reference white,
+      1.0 for SDR; set with the output profile, read by tone mappers **/
+  float output_headroom;
 
   // instances of pixelpipe, stored in GList of dt_dev_pixelpipe_iop_t
   GList *nodes;