wrong "format" for compressed 16bit png images

[christian-rauch]

Creating a CompressedImage in Python via:

img_msg = self.cvbridge.cv2_to_compressed_imgmsg(img, dst_format="png")

where img is is np.uint16, creates a compressed image message with img_msg.format = "png", i.e. it sets format directly to dst_format:

vision_opencv/cv_bridge/python/cv_bridge/core.py

Line 216 in a3736d2

cmprs_img_msg.format = dst_format

However, rqt_image_view only displays the compressed 16bit png image properly when the format is set to:

img_msg.format = "16UC1; png compressed"