When photographing subjects that are destined to be printed in sizes larger that 16 x 20 inches, the process is to shoot the image in RAW at full resolution using a dSLR camera (they have sensors that are over 15 times larger than a P&S camera (telling us you have a 14 mp sensor tells us nothing about your camera, whether it is a P&S or dSLR camera, important information)
After copying the original RAW files to the computer the RAW file is then processed taking into consideration any custom white balance and compensation for the lens brand and focal length used.
Those processed RAW files are then saved as a 16-bit TIFF file, a file that has NO compression and that will produce the highest quality prints. As you can see, the process for printing large files has to be considered BEFORE the photo is captured, this means you have to pre-visualize the shot as well as plan on using your cameras highest resolution.
I just processed a RAW file to be used as a 4x6 foot poster. The resulting TIFF file is about 1.4 gb, yes gb.
Of course when making such large prints, you have to have images that are as close to perfectly exposed and perfectly sharp (NO camera or subject movement and the subject in perfect focus)
