Again, this may seem like an esoteric point, but it means that when you’re starting with raw image data, you’re starting with the overwhelming majority of all your possible gray values in the brightest two stops of any given exposure. Adobe’s Highlight Recovery technology takes advantage of this fact, giving you a lot more control over highlight detail than you would have if you were starting with tone-mapped (JPEG or TIFF) RGB data.
Adjusting exposure is also much more flexible when starting with raw data. Because exposure values in the original scene are recorded linearly, changing exposure in RAW processing is simply scaling the raw values up or down before the process of tone-mapping changes their linear relationship to each other.
The process of squishing this giant range of linear values down to make an image look the way you expect it to look is called “gamma encoding,” or “tone-mapping.” Again, that’s a one-way street. Once you’ve tone-mapped raw values into a lower bit-depth TIFF or JPEG ﬁle, it’s impossible to recover that highlight detail, or accurately move tones up or down with exposure adjustments.
Another benefit of starting with raw is the ﬂexibility you have choosing a white balance. Since the entire range of colors the camera sensor is capable of capturing is stored in the RAW ﬁle, there’s no need to set white balance when shooting RAW. It can be set to any value later in processing. But once raw data is processed and encoded into RGB, it’s much less flexible. If you’re shooting JPEG, you’re relying on the camera to perform the RAW processing, making it essential to have an accurate white balance set at the time of exp
Finally, in the early days of promoting RAW workflows, we were all fond of saying another benefit of keeping your RAW image files was that RAW processing would get better in the future. I barely believed this bit of marketing myself, but it was the release of the 2012 Process Version in Lightroom 4 that changed my mind forever. Going back to older RAW files, I find that I now have a great deal more latitude, especially in highlight recovery. Opening up deep shadow detail can also be done with a much more natural look. The detail was always there in the files; I just never had the tools to pull it off the RAW file until now.
This improved processing isn’t limited to just better control over highlight and shadow detail. Lightroom 4 also brought us lens profiling and the incredibly powerful Lens Correction tools. Lightroom 5 came with vastly better chromatic aberration correction and new defringing controls. Every time I revisit an old RAW file, I find new ways to make my corrections better than the last time I tried.