The preprocessing corrections are not applied by default. These can be employed to address image problems that are particularly problematic and require manual corrections.
These corrections are not affected by the 'Strength' slider.
This is an optional 'gamma' correction, and is great for fixing very under- or over-exposed images. You can use this to recover or add up to five stops of light. If working with a raw file, make these changes in your image processor (such as Adobe Camera Raw or Lightroom) before invoking Perfectly Clear. But this adjustment is particularly useful for small adjustments or dealing with JPEG or TIFF files (not processed in other software).
This allows you to apply a color or corrective filter to your images. These corrections simulate traditional photography filters that would be attached in front of a lens.
In version 3.1, the Neutral Density Corrective Filter has been added to the main Preprocessing tool to allow it to be adjusted more quickly - and now you can apply it as well as one other Corrective Filter.