Add manual brightness/contrast/saturation sliders to color correction screen

[e-t-l]

After scanning and cropping, on the screen that gives color correction options "Original," "Auto," "Grayscale," "B & W," would it be possible to add an optional slider for Contrast and Brightness, and ideally also for Saturation (in Original/Auto modes)? I find that the grayscale mode does not have enough contrast (i.e. too many levels), while black-and-white mode has too much contrast (i.e. only 2 levels). It would be nice for users to be able to control the brightness/contrast/saturation of the scan themselves. Thanks!