The Convert to Duotone filter
You can use the Convert to Duotone filter to convert both color images and black-and-white images into duotones. Duotones increase the tonal range of a grayscale image by using different colors to reproduce different gray levels.
The Convert to Duotone filter
To create a duotone in an image
Select an image file.
On the Window menu, click Image Editor.
Click the Convert to Duotone filter.
In the Convert to Duotone dialog box, select a light and dark color by clicking the respective color buttons.
Adjust the brightness and contrast by using the sliders. Negative numbers reduce brightness and contrast.