Add support for alpha pngs by adding per stream type decode functions (#106)

Co-authored-by: Matthew Bries <[email protected]>

Author: matt-attack

include/web_video_server/image_streamer.h

@@ -55,6 +55,7 @@ class ImageTransportImageStreamer : public ImageStreamer
   virtual void start();
 
 protected:
+  virtual cv::Mat decodeImage(const sensor_msgs::ImageConstPtr& msg);
   virtual void sendImage(const cv::Mat &, const ros::Time &time) = 0;
   virtual void restreamFrame(double max_age);
   virtual void initialize(const cv::Mat &);

include/web_video_server/png_streamers.h

@@ -19,6 +19,7 @@ class PngStreamer : public ImageTransportImageStreamer
   ~PngStreamer();
 protected:
   virtual void sendImage(const cv::Mat &, const ros::Time &time);
+  virtual cv::Mat decodeImage(const sensor_msgs::ImageConstPtr& msg);
 
 private:
   MultipartStream stream_;
@@ -42,6 +43,7 @@ class PngSnapshotStreamer : public ImageTransportImageStreamer
   ~PngSnapshotStreamer();
 protected:
   virtual void sendImage(const cv::Mat &, const ros::Time &time);
+  virtual cv::Mat decodeImage(const sensor_msgs::ImageConstPtr& msg);
 
 private:
   int quality_;

src/image_streamer.cpp

@@ -81,6 +81,29 @@ void ImageTransportImageStreamer::restreamFrame(double max_age)
   }
 }
 
+cv::Mat ImageTransportImageStreamer::decodeImage(const sensor_msgs::ImageConstPtr& msg)
+{
+  if (msg->encoding.find("F") != std::string::npos)
+  {
+    // scale floating point images
+    cv::Mat float_image_bridge = cv_bridge::toCvCopy(msg, msg->encoding)->image;
+    cv::Mat_<float> float_image = float_image_bridge;
+    double max_val;
+    cv::minMaxIdx(float_image, 0, &max_val);
+
+    if (max_val > 0)
+    {
+      float_image *= (255 / max_val);
+    }
+    return float_image;
+  }
+  else
+  {
+    // Convert to OpenCV native BGR color
+    return cv_bridge::toCvCopy(msg, "bgr8")->image;
+  }
+}
+
 void ImageTransportImageStreamer::imageCallback(const sensor_msgs::ImageConstPtr &msg)
 {
   if (inactive_)
@@ -89,25 +112,7 @@ void ImageTransportImageStreamer::imageCallback(const sensor_msgs::ImageConstPtr
   cv::Mat img;
   try
   {
-    if (msg->encoding.find("F") != std::string::npos)
-    {
-      // scale floating point images
-      cv::Mat float_image_bridge = cv_bridge::toCvCopy(msg, msg->encoding)->image;
-      cv::Mat_<float> float_image = float_image_bridge;
-      double max_val;
-      cv::minMaxIdx(float_image, 0, &max_val);
-
-      if (max_val > 0)
-      {
-        float_image *= (255 / max_val);
-      }
-      img = float_image;
-    }
-    else
-    {
-      // Convert to OpenCV native BGR color
-      img = cv_bridge::toCvCopy(msg, "bgr8")->image;
-    }
+    img = decodeImage(msg);
 
     int input_width = img.cols;
     int input_height = img.rows;

src/png_streamers.cpp

@@ -1,6 +1,8 @@
 #include "web_video_server/png_streamers.h"
 #include "async_web_server_cpp/http_reply.hpp"
 
+#include <cv_bridge/cv_bridge.h>
+
 namespace web_video_server
 {
 
@@ -18,6 +20,21 @@ PngStreamer::~PngStreamer()
   boost::mutex::scoped_lock lock(send_mutex_); // protects sendImage.
 }
 
+cv::Mat PngStreamer::decodeImage(const sensor_msgs::ImageConstPtr& msg)
+{
+  // Handle alpha values since PNG supports it
+  if (sensor_msgs::image_encodings::hasAlpha(msg->encoding))
+  {
+    return cv_bridge::toCvCopy(msg, "bgra8")->image;
+  }
+  else
+  {
+    // Use the normal decode otherwise
+    return ImageTransportImageStreamer::decodeImage(msg);
+  }
+}
+
+
 void PngStreamer::sendImage(const cv::Mat &img, const ros::Time &time)
 {
   std::vector<int> encode_params;
@@ -64,6 +81,20 @@ PngSnapshotStreamer::~PngSnapshotStreamer()
   boost::mutex::scoped_lock lock(send_mutex_); // protects sendImage.
 }
 
+cv::Mat PngSnapshotStreamer::decodeImage(const sensor_msgs::ImageConstPtr& msg)
+{
+  // Handle alpha values since PNG supports it
+  if (sensor_msgs::image_encodings::hasAlpha(msg->encoding))
+  {
+    return cv_bridge::toCvCopy(msg, "bgra8")->image;
+  }
+  else
+  {
+    // Use the normal decode otherwise
+    return ImageTransportImageStreamer::decodeImage(msg);
+  }
+}
+
 void PngSnapshotStreamer::sendImage(const cv::Mat &img, const ros::Time &time)
 {
   std::vector<int> encode_params;