Yes, a RAW file is like a negative. A PSD file is like a print.
The RAW file contains all the original data recorded by the camera. A PSD file renders the RAW data into an image humans can comprehend. The PSD file may have no input from the photographer when it is first rendered in CS2, but there is human semi-subjective input. For instance the PSD will use the white balance setting in the camera when the photo was recorded. But the RAW data contains no color temperature information whatsoever. The same goes for display sharpening and noise filtering.
Shooting in RAW has several advantages. The RAW file contains all the information recorded by the sensor. In-camera jpegs throw away large amounts of sensor information in order to provide convenience. If the scene is perfectly exposed (or even well-exposed), the discarded data is not required by the human eye and brain to properly perceive the image. Sadly the RAW to jpeg conversion software knows nothing at all about how well the image was exposed. The people who designed the software had no choice but to assume the exposure was perfect. Unfortunately I am not able to achieve perfection with every exposure, so I prefer to shoot in RAW whenever possible. I can make decisions about what data from the RAW image should be used to best represent the scene/subjects. The better the exposure, the less important my decisions become – and vice-versa. Once I have the optimum version of the RAW image, I can convert it to a jpeg knowing the discarded information is not needed.
Adobe LightRoom, or a similar program, would make more sense. LR renders the RAW data and lets you process the image to suit your needs. LR never modifies the RAW data. PSDs aare not required for image processing. LR keeps a detailed database (called a Catalog in LR) that records every modification you make to the rendered RAW image. Every time a RAW image is viewed in LR the processing steps are applied to the original RAW data to recreate the rendered image. The image is never duplicated which is much more efficient. Upon export for viewing outside of LR or printing, a new, separate file is created (usually a jpeg).
Finally, LR can transfer a rendered version of the RAW data to Photoshop (maybe even CS2, who knows?). You can process the image with more powerful tools if LR's tool are inadequate (LR does not use layers) and then import the resulting
PSD file into LR as a new separate file.
