added dominantColor function

README.md

@@ -49,6 +49,7 @@
       0. [GIF](#gif)
     0. [Write to file](#write-to-file)
     0. [Get metadata](#get-metadata)
+    0. [Get dominant color](#get-dominant-color)
   0. [Batch operations](#batch-operations)
 0. [Copyrights](#copyrights)
 
@@ -706,6 +707,14 @@ tEXt chunks in PNG images, and will get the first tEXt chunk found with the key
 
 `image.getMetadata()`
 
+### Get dominant color
+
+Get the pixel color that occurs most frequently in a picture.
+
+`image.dominantColor(pixels_to_skip)`
+
+0. `pixels_to_skip {Int}`: the number of pixels to skip while iterating through the image. Ex. supplying 1 will skip every other pixel, 0 will skip none. The greater the number the less accuracy the result will have.
+
 ### Batch operations
 
 Each of the [image operations](#image-operations) above can be done as part of

lib/BatchPrototypeInit.js

@@ -37,6 +37,7 @@
         exec: decree(defs.args.exec),
         toBuffer: decree(defs.args.toBuffer),
         writeFile: decree(defs.args.writeFile)
+
     };
 
     var undefinedFilter = util.undefinedFilter,

lib/ImagePrototypeInit.js

@@ -35,7 +35,8 @@
         toBuffer: decree(defs.args.toBuffer),
         writeFile: decree(defs.args.writeFile),
         setPixel: decree(defs.args.setPixel),
-        getPixel: decree(defs.args.getPixel)
+        getPixel: decree(defs.args.getPixel),
+        dominantColor: decree(defs.args.dominantColor)
     };
 
     Image.prototype.__lock = function() {
@@ -68,6 +69,51 @@
         return this.__lwip.height();
     };
 
+
+
+    Image.prototype.dominantColor = function() {
+      var that = this,
+          ret_pixel;
+      judges.dominantColor(
+        arguments,
+          function(skips){
+            if(typeof skips !== 'number' || skips < 0 || parseInt(skips,10) !== skips)
+              throw Error("Pass a positive integer argument for number of pixels to skip over each iteration.");
+
+            var hash = {};
+
+            for(var i = 0; i < that.width(); i++){
+              for(var j = 0; j < that.height(); j+= skips+1){
+                var pixel = that.__lwip.getPixel(i,j),
+                    key = pixel[0].toString()+','+pixel[1].toString()+','+pixel[2].toString()+','+pixel[3].toString(),
+                    occur = hash[key];
+                if( occur === undefined)
+                  hash[key] = 1;
+                else
+                  hash[key]++;
+              }
+            }
+
+            var the_key = '0,0,0,0', count = 0;
+            for(var key in hash){
+              if(hash[key] > count){
+                the_key = key;
+                count = hash[key];
+              }
+            }
+            the_key = the_key.split(',');
+
+            ret_pixel = {
+              r: parseInt(the_key[0],10),
+              g: parseInt(the_key[1],10),
+              b: parseInt(the_key[2],10),
+              a: parseInt(the_key[3],10)
+            };
+        }
+      );
+      return ret_pixel;
+    };
+
     Image.prototype.size = function() {
         return {
             width: this.__lwip.width(),
@@ -114,6 +160,7 @@
         );
     };
 
+
     Image.prototype.resize = function() {
         this.__lock();
         var that = this;

lib/defs.js

@@ -192,6 +192,10 @@
             name: 'callback',
             type: 'function'
         }],
+        dominantColor: [{
+            name: 'type',
+            type: 'number'
+        }],
         darken: [{
             name: 'delta',
             type: 'number'

tests/01.getters/index.js

@@ -104,3 +104,44 @@ describe('lwip.getMetadata', function() {
         });
     });
 });
+
+describe('lwip.dominantColor',function(){
+  var t_image;
+  before(function(done){
+    lwip.open(imgs.jpg.colors, function(err, img) {
+      if (err) return done(err);
+      t_image = img;
+      done();
+    });
+  });
+
+  it('should return the color that occurs the most frequently',function(done){
+      var color = t_image.dominantColor(10);
+      assert( color.r === 255);
+      assert( color.g === 252);
+      assert( color.b === 0);
+      assert( color.a === 100);
+      done();
+  });
+
+  function shouldFail(fail){
+    it('should fail when: '+fail+' is passed as a parameter',function(done){
+      var err_count = 0;
+      try{
+        t_image.dominantColor(fail);
+      }
+      catch(error){
+          err_count++;
+      }
+      finally{
+        assert( err_count === 1);
+      }
+      done();
+    });
+  }
+
+  var fails = [ -1, 3.3, '\'tree\''];
+  for(var i = 0; i < fails.length; i++)
+    shouldFail(fails[i]);
+
+});

tests/imgs.js

@@ -7,7 +7,9 @@ module.exports = {
         gs: join(__dirname, imbase, 'gs.jpg'),
         rgb: join(__dirname, imbase, 'rgb.jpg'),
         noex: join(__dirname, imbase, 'rgbjpg'),
-        inv: join(__dirname, imbase, 'invalid.jpg')
+        inv: join(__dirname, imbase, 'invalid.jpg'),
+        colors: join(__dirname, imbase, 'colors.jpg')
+
     },
     png: {
         gs: join(__dirname, imbase, 'gs.png'),