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Is there a nice way to convert the built-in JPEG compressed image message to an AWT BufferedImage?

asked 2013-04-05 09:26:56 -0600

dljsjr gravatar image

updated 2013-04-05 09:28:50 -0600

Like it says on the tin, we need to process a compressed_image transport from Java code. We aren't developing on Android and so can't leverage any of the Android-specific stuff packaged in to rosjava.

Specifically, we need to go from a CompressedImage message to a native AWT BufferedImage. But to do this, we need a lot of information required to decompress the image that we can't seem to get a hold of (things like width and height, which I suppose we could get from the CameraInfo but we're trying to keep the number of subscription handlers to a minimum because they seem to be pretty heavyweight in all of our benchmarks).

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answered 2013-04-05 10:35:50 -0600

dljsjr gravatar image

Looks like this was as simple as using a ByteArrayInputStream and ImageIO.read(). We ran in to some hiccups because we forgot to offset from the ChannelBuffer but we got it figured out.

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Hey, working on the same problem, what do you mean by offset the ChannelBuffer?

Robocop87 gravatar imageRobocop87 ( 2014-12-15 05:28:10 -0600 )edit

I'm having the same problem also, could you post more details about your solution?

jubeira gravatar imagejubeira ( 2017-04-11 14:28:56 -0600 )edit
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answered 2017-04-17 08:01:29 -0600

jubeira gravatar image

updated 2017-04-17 08:55:31 -0600

For the record, here's the way I found to subscribe to a compressed image topic and save the received images to files using rosjava (no Android required):

@Override
public void onStart(ConnectedNode node) {
  final Log log = node.getLog();
  latch = new CountDownLatch(0);
  Subscriber<CompressedImage> subscriber = node.newSubscriber(topic, "sensor_msgs/CompressedImage");
  log.info("Subscribed to " + topic);

  subscriber.addMessageListener(new MessageListener<CompressedImage>() {
      @Override
      public void onNewMessage(CompressedImage message) {
          log.info("New image is here! Format: " + message.getFormat());

          if (!message.getFormat().contains("jpeg")) {
              log.warn("Only jpeg images are supported");
              return;
          }

          // The latch allows the node to finish saving the image before a new one arrives.
          if (latch.getCount() == 0) {
              latch = new CountDownLatch(1);
              ChannelBuffer buffer = message.getData();
              log.info("Array length: " + buffer.array().length);
              try {
                  // Look for the start of the image inside the buffer
                  // In the tests with TangoRosStreamer, the offset is always 0x3F,
                  // perhaps it's not necessary to search for the index every time.
                  int imageStart = Bytes.indexOf(buffer.array(), JPG_START);
                  if (imageStart < 0) {
                      throw new Exception("Invalid JPG format: start not found");
                  }

                  File outputFile = new File("image_" + Integer.toString(imgNumber) + ".jpg");
                  OutputStream outStream = new FileOutputStream(outputFile);
                  outStream.write(buffer.array(), imageStart, buffer.array().length - imageStart);
                  log.info("Wrote file");
                  outStream.close();
                  imgNumber++;
              } catch (Exception e) {
                  System.out.println("Listener exception: " + e.getClass() + " msg: " + e.getMessage());
              } finally {
                  latch.countDown();
              }
          }
      }
  });
}

The byte array can also be converted to a BufferedImage after getting the index of the start (see this answer: http://stackoverflow.com/questions/12... )

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Asked: 2013-04-05 09:26:56 -0600

Seen: 690 times

Last updated: Apr 17 '17