You can adjust the exposure slightly
I think you can't in reality adjust the exposure. The exposure is how long the CCD was exposed to the optical image and through what aperture. That was chosen by you or the camera when you pushed the button.
What you can do afterwards on a 'RAW' image is alter the brightness&colour balanceof the pixels, which is not the same thing. If a pixel was overexposed in a bright highlight, or completely black in a shadow, there's nothing you can do to get it back. That was determined when you pushed the button.
The exposure, the image recorded by the CCD, isbased on anoriginal mechanical event, involving an iris diaphragm and anelectronic timer. That's real photography as it's always been. After that it's all data processing.