Adds preview functions

DescriptorManager.cpp

@@ -256,4 +256,14 @@ void DescriptorManager::outputRank(string imagename, int method) {
 	for (std::multiset<pair<unsigned long long, string>>::iterator it = distances.begin(); it != distances.end(); ++it) {
 			cout << "(" << it->first << ", " << it->second << ")" << endl;
 	}
+}
+
+//Just runs the preview functions of all the descriptors on given image.
+//No need to init before this.
+void DescriptorManager::generatePreviews(string imagename) {
+	fs::path imagePath(img_path / imagename);
+	Image* img = new Image(imagePath.generic_string());
+	for (int i = 0; i < numDescriptors; i++) {
+		descriptor_types[i]->preview(img);
+	}
 }