You can make a picture into a negative of itself so that every shade takes on its correspondingly opposite shade.

1. Select the cropping tool from the tool bar, and then select the picture whose image you want to fine-tune.

2. Choose Image Control from the Edit menu.

3. Select Negative.

4. Click Apply to see the results. Any changes that you previously made are included in the reversal of greys to create the negative.

5. Click OK when you're done.
   
   To return to a positive of the selected picture, uncheck the Negative option, click Apply, and then click OK.