RectifyNodelet was not subscribing to image_mono

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I am trying to customize Imageproc node to add a time stamp on each input frame. The output from mono was perfectly fine. The Image from mono has time stamp on it.

But the RectifyNodelet was not able to subscribe to It. I have converted raw_msg to a cv::Mat and the used putText for stamping arrival time on it. Then converted the same to sensors:msg using CvImage().toImageMsg

Could anybody please let me know what might be the reason.