The tone curve

Use point curves to adjust overall tone or individual red, green and blue channels.

The curve group sits between Tone and Colour. Select RGB, R, G or B, then click the plot to add a point and drag it to adjust. Each channel supports up to sixteen points. Double-click an interior point to remove it. Endpoints can move but cannot be removed.

Curve interpolation preserves point order and avoids overshoot between neighbours. Values use the sRGB-encoded range. A luminance histogram appears behind the plot on the same axes.

Adjust from the photograph. Press T or click the target button in the header. Drag vertically on the photograph to brighten or darken the sampled tone in the active channel. Sampling excludes the curve so it measures the curve’s input. Each drag is one undo step. The tool stays active between drags. The button reads Done while it is active; that button, T, esc, a click on the border around the photograph, folding the Tone curve group, or dragging any other control turns it off.

While the tool is active, moving the pointer shows the sampled tone as a filled dot on the curve, with input and output values below. Moving the pointer alone does not save an edit or rerender the photograph.

The point editor. Click the point-editor button beside the readout below the plot to list the active channel’s points. Select a point, then type its input and output values or press Adjust to move it with the arrow keys. You can also add a point in the widest gap or delete an interior point. The editor opens beside the sidebar and stays open while you drag points on the plot, so their values remain visible. Click the point-editor button again to close it.

Preview and points. Hovering over the plot shows input and output values. Clicking an identity curve can place a temporary point without marking the photograph edited. It is saved only after moving off the diagonal. Changing channels, changing photographs or selecting ORIGINAL discards the temporary point. At sixteen points, the add-point handle dims until a point is removed.

Colour ribbon and other curves. The ribbon under the plot shows the colour produced at each tone by all four curves. Adjusted channels appear as thin curves behind the active channel; unchanged channels are omitted. Applied looks show dashed reference curves. Your curve and the look’s curve combine, and the look’s Amount affects the displayed result. Bypassing the curve group makes the ribbon neutral.

Copy curves. Right-click the plot or a channel button to act on that channel, even when another is displayed:

• Copy curve and Paste curve transfer one channel, including between Background and mask layers.
• Copy all channels and Paste all channels transfer all four.
• Apply RGB to the other channels, or the corresponding named channel, copies its shape to the others.

Applying the composite RGB curve to R, G and B resets RGB to the diagonal in the same step, preserving the rendered result. The curve clipboard lasts for the session and is separate from treatment copying with ⇧⌘C and ⇧⌘V.

Curves support group RESET, bypass and undo. Identity curves are not stored as edits. Tone sliders and curves are evaluated together over the cached RAW decode, so curve dragging has similar cost to Tone dragging.