Adds preview functions

Descriptor.h

@@ -32,6 +32,12 @@ public:
 		return true;
 	}
 
+	//Function which should output some example(s) to file
+	//that show how this descriptor works.
+	virtual void preview(Image* img) {
+		cout << "No preview defined. :-( " << endl;
+	}
+
 	//Helper functions
 	//TODO: Move these somewhere else. Maybe a friend-class?
 	double* CalculateDCT(Image* img) {
@@ -125,7 +131,7 @@ public:
 		int green_b = (b << (64 - 16) >> (64 - 8)).to_ulong();
 		int blue_b = (b << (64 - 8) >> (64 - 8)).to_ulong();
 		return abs(red_a - red_b) + abs(green_a - green_b) + abs(blue_a - blue_b);
-	};
+	}
 	string ToString() {
 		return "averageColor";
 	}
@@ -332,7 +338,7 @@ public:
 			if (a[i] != b[i]) biterror++;
 		}
 		return biterror;
-	};
+	}
 	string ToString() {
 		return "threshold";
 	}
@@ -365,10 +371,19 @@ public:
 			if (a[i] != b[i]) biterror++;
 		}
 		return biterror;
-	};
+	}
 	string ToString() {
 		return "DCTPearson";
 	}
+	void preview(Image* img){
+		Image* dct = new Image(*img);
+		Image* local_image = new Image(*img);
+
+		//double* converted = CalculateDCsT(dct);
+		local_image->type(GrayscaleType);
+		local_image->sample(Geometry("8x8!")); //64 pixels
+		local_image->write("DCTPearson.png");
+	}
 };
 
 class DCTMedian : public Descriptor {
@@ -398,7 +413,7 @@ public:
 			if (a[i] != b[i]) biterror++;
 		}
 		return biterror;
-	};
+	}
 	string ToString() {
 		return "DCTMedian";
 	}