Republishing CompressedDepth image to Raw image

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I am using the following command to republish compressed depth images to raw message topics:

rosrun image_transport republish compressedDepth in:=/camera/depth/image_raw/ raw out:=/camera/depth/image_raw

However, the above command throws the following error at runtime:

terminate called after throwing an instance of 'std::runtime_error'
  what():  Unknown encoding png
[1]    1475 abort (core dumped)  rosrun image_transport republish compressedDepth  raw