To convert an image to a duotone, you change a bitmap to the grayscale color mode and enhance it using one to four additional colors, giving the image greater tonal depth. When you change an image to a duotone, a tone curve grid that represents the dynamic tone curves that are used throughout the conversion is displayed. The horizontal plane (x-axis) displays the 256 possible shades of gray in a grayscale image (0 is black, 255 is white). The vertical plane (y-axis) indicates the intensity of a color (from 0 to 100 percent) that is applied to the corresponding grayscale values. For example, a grayscale pixel with a color value of 25 is printed with a 25-percent tint of the color. By adjusting the tone curves, you can control the color and intensity of the tone that is added to an image. When you change an image to a duotone, you can specify the colors to overprint when you print an image. Overprint colors are used to preserve color integrity when inks overlap. When you display the image, each color is applied on the screen in sequence, creating a layered effect. You can view all instances in which the colors you choose for the duotone conversion overlap. Associated with each instance is the color that is produced by the overlap. You can also choose new overprint colors to see how they overlap. Duotones will hold their color ink information when saving to Encapsulated PostScript (EPS), Portable Document Format (PDF) and CorelDRAW (CDR) file formats. Other file formats don’t support duotone images. If you want to adjust the color’s tone curve, click the ink tone curve on the grid to add a node, and drag the node to adjust the percentage of color at that point on the Source.