For this exercise we are to take an image of someone in part shade and selecting them and make an enhancement such as a levels or curves adjustment. For my image I also chose a bright background. Normally you would use a fill flash for this type of photography and I have later shown how the raw conversion 'fill light' has helped.
Here is the original image, as seen the subject is in shade which does not produce a pleasing image.
I then used the lasso tool to select around the subject, then refining it with shift (add) and alt (minus) keys to get as good a selection as possible. I find that a poor selection is obvious when boosting part of a high contrasting image. After saving the selection I then feathered the selection by 20px.
Using the levels adjustment I then brought in the right hand slider to meet the edge of the histogram which has produced the following, this I feel is a good improvement, that is not unrealistic.
Pushing the levels further produces an image that I think has too much manipulation and does not work. Perhaps adding more contrast and saturation may help but that would also darken the selection as well.
Finally, using the raw converter and the fill light slider at 53 produced this image. This is remarkably similar to the first version that has been adjusted with a selection, but the raw conversion has done this with no selection!