The ROS image pipeline is run with the image_proc package. It provides all the conversion utilities for obtaining monochrome and color images from the RAW images acquired from the camera. In the case of FireWire cameras, which may use a Bayer pattern to code the images (actually in the sensor itself), it debayers them to obtain the color images. Once you have calibrated the camera, the image pipeline takes the CameraInfo messages, which contain that information, and rectifies the images. Here, rectification means to un-distort the images, so it takes the coefficients of the distortion model to correct the radial and tangential distortion.
As a result, you will see more topics for your camera in its namespace. In the following screenshots, you can see the image_raw, image_mono, and image_colour topics, which display the RAW, monochrome, and color images, respectively:
The mono color, in this case, is equivalent to the following raw image. Note that for good cameras the...