The Tone Curve is an extension to the basic Sliders and thus provides a greater level of tone and contrast control by allowing the user to modify the various different levels of light within a photograph.

One of the most apparent such features is the little circle on the “top Left Corner” of the Curve Box. By clicking on this little circle, the circle will show 2 arrows, one above and one below the circle. This means that the user can now actively Drag the Cursor over the image with the left click pressed and change the tonal values of the image whilst hovering over the image.

The changes in the image are visible in the Tone Curve box which changes with each adjustment of the selected light level, however, the changes made are global, and affect all the pixels within the image and not just the area where you are hovering.

Where the tone curve becomes very powerful and differentiates from the sliders, is using the "individual points editor”, located at the bottom right corner of the Tone Curve box.

Here you can can adjust and lock different points of the graph without affecting other adjustments. An example will be to drag it up from the centre to increase exposure. lock it in place and then reduce the curve in the middle of this point and the end of the curve to the right and bring down the highlights and then lock the point. Alternatively, you can do the same on the other side of the curve to increase or decrease shadows.

You can do this for RGB or Red, Green and Blue individually, and none of these changes affect any basic slider adjustments that you may have already made.

A good practice is to adjust using the basic, Highlight, Shadows, Whites and Blacks sliders first, and then fine tune with the Tone Curve.