yuv422_yuy2 incorrectly (de)compressed

[StefanFabian]

Hey,
using usb_cam and my webcam, the image is published as yuv422_yuy2.
The compressed topic has the encoding yuv422_yuy2; jpeg compressed mono8 (which sounds like it doesn't really support compressing yuv and compresses the data as mono8).
When I receive this image with image_transport, I get the original encoding but the step size is incorrect.
YUV has a bit depth of 16bits but the step size of the decompressed image is equal to the width of the image not 2 * the width like it should be and the uncompressed image is.

[emrekuru97]

Hey, same situation here, exaclty with the encoding yuv422_yuy2 and plus the encoding yuv422 in compressed image. I don't know where this is done in code, bu a fix would be nice. But I have no problem with the raw_image.

[milidam]

I encountered the same kind of issue, and spent some time understanding why.

It looks like yuv422_yuy2 is not completely supported by the image_transport_plugins project:

In the compressed_image_transport's CompressedPublisher, a yuv422_yuy2-encoded Image is considered as a "colored" one by the enc::isColor(message.encoding) condition, so that the targetFormat becomes bgr8 in the encoded CompressedImage.

On the other hand, at the decoding by the CompressedSubscriber, the JPEG frame is properly extracted by cv::imdecode into a cv::Mat structure; with the default cfg_imdecode_flag (unchanged mode), it thus probably contains RGB channels.
However, the image_encoding is set to yuv422_yuy2, without that the cv::Mat is actually converted to that format.

By manually changing the COmpressedImage's format from yuv422_yuy2; jpeg compressed bgr8 to bgr8; jpeg compressed bgr8 allows for a proper decoding.
However, the resulting decompressed image's encoding is now bgr8, instead of the original yuv422_yuy2.

To fix that, I would expect, somehow, that a case like the following should added to the CompressedSubscriber's internalCallback decoding block

          if ((image_encoding == enc::YUV422_YUY2) || (image_encoding == enc::YUYV)) {
            cv::cvtColor(cv_ptr->image, cv_ptr->image, CV_BGR2YUV);
          }