added more comments on the png compression format for depth images

Author: saikishor

src/gazebo_ros_realsense.cpp

@@ -41,6 +41,7 @@ void GazeboRosRealsense::Load(physics::ModelPtr _model, sdf::ElementPtr _sdf) {
   this->itnode_ = new image_transport::ImageTransport(*this->rosnode_);
 
   // set 'png' compression format for depth images
+  // default functional parameters for compressed_image_transport to have lossless png compression
   rosnode_->setParam(rosnode_->resolveName(cameraParamsMap_[DEPTH_CAMERA_NAME].topic_name) + "/compressed/format", "png");
   rosnode_->setParam(rosnode_->resolveName(cameraParamsMap_[DEPTH_CAMERA_NAME].topic_name) + "/compressed/png_level", 1);