[gegl] workshop: add a gray component replacement implementation

[Øyvind "pippin" Kolås <ok src gnome org>]

commit a472e833dac808903fa2eddd7a2053be5005c385
Author: Øyvind Kolås <pippin gimp org>
Date:   Mon Dec 3 23:04:48 2018 +0100

    workshop: add a gray component replacement implementation
    
    This implementation assumes that C=M=Y is gray, this could be
    improved by extracting some more information from the ICC profile
    of the space. However the changes when converted to RGB for display
    by GEGL using applications will be wysiwyg.
    
    For now the inklimit slider has to be pushed to the right for the
    final render. It might well be better to have two separate ops
    for this and juggle them in ui code instead.

 operations/workshop/Makefile.am |   1 +
 operations/workshop/gcr.c       | 122 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 123 insertions(+)
---
diff --git a/operations/workshop/Makefile.am b/operations/workshop/Makefile.am
index b1985416d..faacec525 100644
--- a/operations/workshop/Makefile.am
+++ b/operations/workshop/Makefile.am
@@ -17,6 +17,7 @@ ops = \
        ditto.la \
        domain-transform.la \
        gradient-map.la \
+       gcr.la \
        hstack.la \
        enlarge.la \
        aces-rrt.la \
diff --git a/operations/workshop/gcr.c b/operations/workshop/gcr.c
new file mode 100644
index 000000000..463a5534e
--- /dev/null
+++ b/operations/workshop/gcr.c
@@ -0,0 +1,122 @@
+/* This file is an image processing operation for GEGL
+ *
+ * GEGL is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * GEGL is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with GEGL; if not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright 2018 Øyvind Kolås <pippin gimp org>
+ */
+
+#include "config.h"
+#include <glib/gi18n-lib.h>
+
+#ifdef GEGL_PROPERTIES
+
+  property_double (inklimit, "Inklevel warn", 250.0)
+  value_range (0.0, 400.0)
+
+  property_double (amount, "amount", 100.0)
+  value_range (0.0, 100.0)
+
+
+#else
+
+#define GEGL_OP_POINT_FILTER
+#define GEGL_OP_NAME     gcr
+#define GEGL_OP_C_SOURCE gcr.c
+
+#include "gegl-op.h"
+#include <stdio.h>
+
+static gboolean
+process (GeglOperation       *op,
+         void                *in_buf,
+         void                *out_buf,
+         glong                samples,
+         const GeglRectangle *roi,
+         gint                 level)
+{
+  GeglProperties *o = GEGL_PROPERTIES (op);
+
+  glong   i;
+  float *in  = in_buf;
+  float *out = out_buf;
+
+  for (i=0; i<samples; i++)
+    {
+      float C = in[0];
+      float M = in[1];
+      float Y = in[2];
+      float K = in[3];
+#if 1
+      float mincol = C;
+      float pullout;
+
+      if (M < mincol) mincol = M;
+      if (Y < mincol) mincol = Y;
+
+      pullout = mincol * o->amount / 100.0;
+
+      C = (C - pullout) / (1.0 - pullout);
+      M = (M - pullout) / (1.0 - pullout);
+      Y = (Y - pullout) / (1.0 - pullout);
+
+      K = 1.0- ((1.0 - K) * (1.0- pullout));
+
+      if (C + M + Y + K > o->inklimit / 100.0)
+      {
+        C = 0; Y= 0; M = 1.0; K=0.0;
+      }
+#endif
+
+      out[0]=C;
+      out[1]=M;
+      out[2]=Y;
+      out[3]=K;
+      out[4]=in[4];
+
+      in += 5;
+      out+= 5;
+    }
+  return TRUE;
+}
+
+static void prepare (GeglOperation *operation)
+{
+  const Babl *format = gegl_operation_get_source_format (operation, "input");
+  format = babl_format_with_space ("CMYKA float", format);
+  gegl_operation_set_format (operation, "input", format);
+  gegl_operation_set_format (operation, "output", format);
+}
+
+
+static void
+gegl_op_class_init (GeglOpClass *klass)
+{
+  GeglOperationClass            *operation_class;
+  GeglOperationPointFilterClass *point_filter_class;
+
+  operation_class    = GEGL_OPERATION_CLASS (klass);
+  point_filter_class = GEGL_OPERATION_POINT_FILTER_CLASS (klass);
+
+  operation_class->prepare = prepare;
+  point_filter_class->process = process;
+
+  gegl_operation_class_set_keys (operation_class,
+    "name"        , "gegl:gcr",
+    "categories"  , "color",
+    "title"       , "Gray Component Replacement",
+    "description" , "Reduces total ink-coverage by transferring color from CMY to K component",
+    NULL);
+}
+
+#endif