How to extract depth data from rosbags(contains depth and RGB data) as picture frames

I have a Bagfile containing Raw depth and RGB data. I converted the RGB data into images using the tutorial http://wiki.ros.org/rosbag/Tutorials/Exporting%20image%20and%20video%20data But when I used the same for converting raw depth to images, I get an error stating " cannot convert 32FC1 to RGB8". This is my launch file: I went through Google for various suggestions given to do the same but I being a beginner find most of the solution vague or misleading and I end up confusing myself. I need to know whether my approach was right or should I do something else? If so what should I do exactly.Please help me through this