One of the easiest, yet effective ways to tone a photograph is to use Gradient Map adjustment layer. The technique is very straightforward: add Gradient Map adjustment layer and play with the colors and sliders.
One of the advantages of this method is you get instant visual feedback of the changes before you apply them, whether you change colors or opacity. You still have the flexibility to combine the Gradient Map adjustment layer with different Blending modes and/or Blend If settings.
Gradient Map adjustment layer can be used give the photo black-and-white treatment, to simulate duotones as well as basic split-toning effects. Play with the sliders, change the Smoothness setting, change the opacity of the stops, change the color, add stops, remove stops, move the color midpoint. The possibilities are endless and best of all, this technique is non-destructive and can be fine-tuned any time.
I usually save interesting settings to a separate Gradient Map "GRD" file, so I can recall the settings with one mouse click. This gives added flexibility to back-up all useful gradient maps and use them on another computer. I usually have a copy of my gradient maps on a memory stick.
Take a look at the examples. Only one Gradient Map adjustment layer was applied to achieve the desired toning.
