Curve editing: options and buttons

Option/button	Description
Channel	Separation to which the curve will be applied. Example: The red channel of an RGB image.
Preview	Enabled: Displays a preview of the changes on the PDF document. Tip: Zoom in to speed up the preview display. Remark: As this preview is rendered at a lower resolution than the original image (to speed up the display), there may be some quality loss (e.g. text being less sharp). However, this does not affect the colors.
	Resets the curve.
	You can: Click the curve to add control points to it. Drag control points to edit the curve. Drag control points away from the pane to remove them.
Input - Output	Adjusts a specified input to a specified output brightness value. The curve adjusts correspondingly.
Apply	Applies your changes to the selected images.