@Epicuros wrote:
Thanks for your prompt response Bob. I understand that most often than not a JPEG thumbnail accompanies the RAW file, but when you process RAW images on DPP you have the possibllity of a full screen image and the editing steps are immediately visible. If we were working on a JPEG image, even one with little loss, how valid would be the processing if what we see is a JPEG and not an original RAW image? I find this difficult to conceive... Further, I quite understand why a TIFF file is larger than a JPEG file, but what I don't understand is why it is bigger than a RAW file... I am not a software nerd, so I may be writing nonsense, but we, old guns will never be fully conversant with new tech. 🙂
Don't say that! I'm probably older than you are, and I'm not about to sell us old geezers short. 
The reason a TIFF is larger than a RAW file is that a RAW file records the data exactly as it came from the camera, while TIFF has to deal with the fact that its data could have come from any of a variety of RAW formats and must be recorded in a camera-independent form. One consequence is that it must account for higher resolution (and potentially longer data items) than current cameras normally use.
As for editing, keep in mind that when you're editing a picture, you're just looking at a collection of dots on a screen. Whether the underlying image on which you're working is a JPEG, TIFF, RAW file, or something conceptually different is obscured by implementation detail. The photo editor has to try to ensure that "what you see is what you get", but how it does that is ultimately unimportant. If the final result is, say, a JPEG, then that JPEG must be (assuming that the display or print algorithm does its job correctly) a faithful representation of what the camera saw. As long as that's the case, what goes on in the editor itself is like making sausage: you can't see how it's done and probably wouldn't want to.
So when someone tells you that "what you see (when you're editing a RAW file) is actually a JPEG", that assumes that the editor converts the RAW image to JPEG and turns it over to a JPEG processing module for display. With some editors, maybe that is what happens, but it's not a given. And it doesn't matter anyway, as long as what is done is good enough to satisfy your eyes.
@kvbarkley wrote:Actually, the reason the Tiff is larger is that it takes the bayer image from the sensor and converts it to Full RGB. So the RAW file has only 1 color channel, 1/4 red, 1/4 blue and 1/4 green, while the Tiff has 3 full color channels.
Just what I said! (Although you stated it much more accurately and succinctly.) 
