To give some examples of what I was talking about earlier, firstly this is a before and after of the classic underexposed photo - in this case the camera has tried to balance the very bright snow and the comparatively dark Alfie:
(Bigger version here -
http://johnmcl7.smugmug.com/Other/General/i-TsXRJj9/0/O/Alfiebeforafter.jpg)
I took this picture as a raw file and then used 'fill light' in Lightroom to lift the dark areas without overexposing the rest of the picture to bring the detail back in Alfie's face and body. There's also a White Balance shift as I went for a warmer setting, you can only really do this with a large sensor camera (Digital SLR, micro 4/3, NEX etc.)
I noticed when shooting how underexposed Alfie was against the snow so I set the camera's exposure compensation to +1 stop which in aperture priority mode forces the camera to shoot at half the shutter speed which gives more detail on the dark subjects like Alfie but overexposing other parts of the scene. This shot is an error because I didn't remove the exposure compensation so the camera has overexposed the whole scene:
(Bigger version here -
http://johnmcl7.smugmug.com/Other/General/i-zhHTTJz/0/O/Alfiebeforeafter2.jpg)
In this case I did the opposite action of fill light and instead used the recovery tool to bring back some of the brighter areas which I've managed to get away with mostly because most of the scene is darker, you can see in the after picture the bright areas at the back particularly in the middle are still too bright. This is a problem in shots like this one:
Or this one:
Alfie's exposure is fine straight out of the camera but the snow is far too bright and it can't be brought back, it's so over exposed the detail has been lost so even pushing the raw file as much as possible does very little.
John