Curves Tool

    Menu -> Image -> Curves



Curves Tool
The Curves tool is the most sophisticated tool used to adjust the tonality of images.

Adjust Color Curves
Channel
There are four options: Value for luminosity and contrast; Red, Green, and Blue for saturation.

Reset Channel
This button deletes all changes made to the selected channel.

Reset All
This button deletes all changes made to the all channels.

Main Editing Area Input and Output Value Domains:
The horizontal bar (x-axis) represents input values (they are value levels from 0 to 255).
The vertical bar (y-axis) is only a scale for output colors of the selected channel.

The control curve is drawn on a grid and goes from bottom left corner to top right corner. Pointer x/y position is permanently displayed in top left part of the grid. If you click on the curve, a Control point is created. You can move it to bend the curve. If you click outside of the curve, a control point is also created, and the curve includes it automatically.

So, each point of the curve represents an 'x' level, corresponding to an 'y' color. If, for example, you move a curve segment to the right, id est to highlights, you can see that these highlights are corresponding to darker output tones and that image pixels corresponding to this curve segment will go darker. With color channels, moving right will decrease saturation and can reach the complementary color.

To delete all control points (apart from both ends), click on the Reset Channel button. To delete only one point, move it onto another point or to grid border.

Linear and Logarithmic buttons
These buttons allow to choose the Linear or Logarithmic type of the histogram.

Curve Type
Open
This button allows you to select a file holding curve settings.

Save
This button allows you to save any curves settings you have set to a file that can be loaded later.