“ A Duotone takes a monochrome grayscale image and allows you to take the tonal range, from lightest tones to darkest, and allocate a different color to specific part of the tonal range.” - http://www.luminous-landscape.com

How is a Duotone produced? Well in photoshop, of course. A Duotone is two colors used to bring out the tones of a photo. Duotones became popular when printmakers had a problem with printing black and white photos on computer printers. Black actually has 256 tones to it, which can’t be reproduced on computer printers. So photoshop has made a solution for this printing dilemma.

Duotones have actually brought not only graphic artist to photoshop, but have also found a following in photographers who now use photoshop as a useful tool in printing their images; Duotones are a way to bring the tones of black and white photos. By adding a color to a black and white picture the tonal range can be easily seen in photos. This is why so many photographers utilize duotones in photoshop.