Originally posted by RBellavance The highlight correction affects the RAW in that it is effectively a "1-stop-underexposed-then-pushed" image. If your RAW converter does not recognize the relevant EXIF tags, the image will appears underexposed by 1 stop.
AFAIK, shadow compensation does not affect the RAW file, it is strictly a "curves" tweak done in-camera to produce the JPG.
what I found is that as far as the correction is concerned on JPEG files, each function, highlight protect and shadow detail preserve, modify the JPEG as follows.
If you consider that JPEG with neutral contrast settings produces an image with average greyscale value at about 120, each full stop has a change of about 45 over the range 25-230
by using either function, shadow detail preserve, or highlight protect, the resulting jpeg has at least one full stop more, either below or above the mean value of 120, or both if they are both selected. the impact is a greatly reduced contrast.
as a comparison minimum contrast has 5 stops between 25 and 230 greyscale, maximum contrast has 4 stops. with shadow and highlight protection active, there are between 6 and 7 stops between 25 and 230 greyscale. at each end of the greyscale range the stops become quite nonlinear, but still their range is also expanded, giving 12-13 stops total detectable range compared to between 10 and 11 stops.
How do you test this?
set your camera to give correct exposure with any lens, such that you have at least 7 full stops of adjustment range to maximum shutter speed. then take shots at each shutter speed increment (ideally 1/3 stops) from maximum shutter speed to as low as you want (but ideally 7 stops or more below the "perfect exposure). The test subject should be a uniformly lit, single color surface.
when you have all the shots taken., measure the greyscale value of the histogram in a photo editor and plot greyscale vs shutter speed (log plot)