For the image below I want the shadows to be slightly more open and I want the highlights on the onion to be more flat and more detailed at the same time. That means adding contrast to the highlights and flattening the mid-highlights. I don’t mind if the table goes flat.
1. Start in the top highlight and make a point. Then do this for the next two highlights going down.
2. Select the middle highlight point and simply pull it down a few notches with your down arrow on the keyboard. This will both flatten and add contrast (separation) to the highlights. Notice the histogram location.
3. In the next two points you can pull your mid-tones back to normal and bring up your shadows a smidgen. Then mix and modify all those adjustments. In my case I ended up making the adjustment much more extreme but notice how the curve is not all squiggly. Even though I have many data points on the curve, they are not destroying the tonal integrity of the image.
Master-curve-only iteration (for comparison):