Improving contrast without altering saturation in the Curve tool

The combined RGB mode is usually the first choice for fine-tuning contrast in most images, however, increasing contrast typically results in an increase in saturation. This can be confirmed by checking the color values before and after adjustment.

It may be acceptable in landscapes, but an increase in saturation may not be desirable for certain images such as portraits. When that is the case, the Luma mode should be adopted instead. In most respects, the Luma curve can be adjusted in the same way that you would adjust an RGB curve. In fact, with more extreme adjustments, the Luma curve has a more realistic response. 

1. Go to the Exposure tool tab.
   
   
2. In the Curve tool, select the Luma tab.
   
   
3. Click directly on the slope to add a control point in the tonal region that you want to adjust. The upper-right part of the slope adjusts highlights and the center adjusts mid-tones. The bottom or lower-left part adjusts the shadows.
   
   
4. To decrease or increase contrast in the chosen region, click and drag the control point to left or right.
   
   
5. To lighten or darken the selected region, drag a control point up or down.
   
   
6. Add more points to the curve to adjust other areas. To remove a control point, click and press delete/backspace or drag it off the curve.
   
   
7. As an option, you can also add points by selecting the Curve Point Picker and clicking on the area of your image that you want to adjust in the Viewer.
   
   

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