Add most dominant colour to image stats #640

src/common.cc

@@ -724,4 +724,25 @@ namespace sharp {
     return std::make_tuple(image, alphaColour);
   }
 
+  /*
+    Removes alpha channel, if any.
+  */
+  VImage RemoveAlpha(VImage image) {
+    if (HasAlpha(image)) {
+      image = image.extract_band(0, VImage::option()->set("n", image.bands() - 1));
+    }
+    return image;
+  }
+
+  /*
+    Ensures alpha channel, if missing.
+  */
+  VImage EnsureAlpha(VImage image) {
+    if (!HasAlpha(image)) {
+      std::vector<double> alpha;
+      alpha.push_back(sharp::MaximumImageAlpha(image.interpretation()));
+      image = image.bandjoin_const(alpha);
+    }
+    return image;
+  }
 }  // namespace sharp

src/common.h

@@ -271,6 +271,16 @@ namespace sharp {
    */
   std::tuple<VImage, std::vector<double>> ApplyAlpha(VImage image, std::vector<double> colour);
 
+  /*
+    Removes alpha channel, if any.
+  */
+  VImage RemoveAlpha(VImage image);
+
+  /*
+    Ensures alpha channel, if missing.
+  */
+  VImage EnsureAlpha(VImage image);
+
 }  // namespace sharp
 
 #endif  // SRC_COMMON_H_

src/operations.cc

@@ -27,29 +27,6 @@ using vips::VImage;
 using vips::VError;
 
 namespace sharp {
-
-  /*
-    Removes alpha channel, if any.
-  */
-  VImage RemoveAlpha(VImage image) {
-    if (HasAlpha(image)) {
-      image = image.extract_band(0, VImage::option()->set("n", image.bands() - 1));
-    }
-    return image;
-  }
-
-  /*
-    Ensures alpha channel, if missing.
-  */
-  VImage EnsureAlpha(VImage image) {
-    if (!HasAlpha(image)) {
-      std::vector<double> alpha;
-      alpha.push_back(sharp::MaximumImageAlpha(image.interpretation()));
-      image = image.bandjoin_const(alpha);
-    }
-    return image;
-  }
-
   /*
    * Tint an image using the specified chroma, preserving the original image luminance
    */

src/operations.h

@@ -25,16 +25,6 @@ using vips::VImage;
 
 namespace sharp {
 
-  /*
-    Removes alpha channel, if any.
-  */
-  VImage RemoveAlpha(VImage image);
-
-  /*
-    Ensures alpha channel, if missing.
-  */
-  VImage EnsureAlpha(VImage image);
-
   /*
    * Tint an image using the specified chroma, preserving the original image luminance
    */

src/stats.cc

@@ -86,6 +86,18 @@ class StatsWorker : public Napi::AsyncWorker {
           0.0,  1.0, 0.0);
         laplacian.set("scale", 9.0);
         baton->sharpness = greyscale.conv(laplacian).deviate();
+        // Most dominant sRGB colour via 4096-bin 3D histogram
+        vips::VImage hist = sharp::RemoveAlpha(image)
+          .colourspace(VIPS_INTERPRETATION_sRGB)
+          .hist_find_ndim(VImage::option()->set("bins", 16));
+        std::complex<double> maxpos = hist.maxpos();
+        int const dx = static_cast<int>(std::real(maxpos));
+        int const dy = static_cast<int>(std::imag(maxpos));
+        std::vector<double> pel = hist(dx, dy);
+        int const dz = std::distance(pel.begin(), std::find(pel.begin(), pel.end(), hist.max()));
+        baton->dominantRed = dx * 16 + 8;
+        baton->dominantGreen = dy * 16 + 8;
+        baton->dominantBlue = dz * 16 + 8;
       } catch (vips::VError const &err) {
         (baton->err).append(err.what());
       }
@@ -133,6 +145,11 @@ class StatsWorker : public Napi::AsyncWorker {
       info.Set("isOpaque", baton->isOpaque);
       info.Set("entropy", baton->entropy);
       info.Set("sharpness", baton->sharpness);
+      Napi::Object dominant = Napi::Object::New(env);
+      dominant.Set("r", baton->dominantRed);
+      dominant.Set("g", baton->dominantGreen);
+      dominant.Set("b", baton->dominantBlue);
+      info.Set("dominant", dominant);
       Callback().MakeCallback(Receiver().Value(), { env.Null(), info });
     } else {
       Callback().MakeCallback(Receiver().Value(), { Napi::Error::New(env, baton->err).Value() });

src/stats.h

@@ -48,6 +48,9 @@ struct StatsBaton {
   bool isOpaque;
   double entropy;
   double sharpness;
+  int dominantRed;
+  int dominantGreen;
+  int dominantBlue;
 
   std::string err;
 
@@ -55,7 +58,10 @@ struct StatsBaton {
     input(nullptr),
     isOpaque(true),
     entropy(0.0),
-    sharpness(0.0)
+    sharpness(0.0),
+    dominantRed(0),
+    dominantGreen(0),
+    dominantBlue(0)
     {}
 };