Hue Curves is a powerful effect that allows you to modify the hue, lightness or saturation (HLS) of a shot using an interactive graph.
Hue / Lightness / Saturation
The Hue, Lightness and Saturation toggle buttons on the left of the graph select how the graph affects the image.
The Hist button shows or hides the histogram display in the graph window.
You can select (pick) areas of colour from the image using your mouse, and these areas will be displayed on the graph as an aid to graph manpulation.
Add Point / Delete Point
You can Add or Delete points from the graph by toggling these buttons on, and then clicking on the graph. This allows finer manipulation of the area of the image affected by the effect.
The Scale slider adjusts the scale of the graph shown.
Hue Curves is the only tool that utilizes the top menu of both the Color and the Image panels.
The top buttons on the Image panel select one of six preset points on a spectrum. These presets assign the menu controls of the Color panel to red, yellow, green, cyan, blue, or magenta. When the Color panel is set to [Menu 2], labeled Positive, the knobs adjust hue, luminance and saturation of the selected color. This tool can isolate and adjust several colors in the same layer.
If Color panel [Menu 3], labeled Inverse, is active the selected color is left unchanged and the other 5 points are adjusted.
[Menu 3] Inverse makes it very easy to create black and white images with one color retained.Color panel [Menu 1], labeled All, selects all six points and configures the Hue Curves to work the same as the HLS tool. This might seem redundant but the default processing path puts Hue Curves first in a layer and HLS as last. Hue Curves All is useful for creating duotone and split tone effects in one layer, whilst HLS modifies the layer correction as well as the natural color.