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In the world of four-color (Cyan, Magenta, Yellow and black aka CMYK) printing, duotone is the name given the process of multiple tone printing using two, three or four different color inks. This process requires the press be set up with special inks instead of the standard CMYK inks that are used for four-color printing. Typically the paper is first printed using a dark base color and then a second lighter color is overprinted to fill in, tint, and tone the photograph and, more importantly, add depth. When two colors of inks are used its call duotone, when three inks are used its a tritone, and when four are used it is a quadtone.
As with all photographic techniques there is more than one way to accomplish this technique. Located inconspicuously in Photoshops Image menu (Image > Mode > Duotone) is the Duotone command that can open many creative doors for the photographer interested in making and printing monochrome images. In order to apply the Duotone command, the image must first be in Grayscale mode (Image > Mode > Grayscale.) When starting with a color image, you must first convert it using any of the software thats available, including Photoshops own Black & White (Image > Adjustments > Black and White) conversion, so its always a two-step process.
When you select Image > Duotone you’ll see a dialog box showing the two colors that can be used. To use sets of colors that are guaranteed to work together, click the dialogs Load button to find Adobes Duotone Presets folder. This is true for both Mac OS and Windows versions of the program. In the current version of Adobe Photoshop there are three choices: Gray Black Duotones, Pantone Duotones, and Process Duotones. Open any folder and click on one of the choices. (These presets can be found by going to the Photoshop folder and looking inside the Presets folder, where you will find a Duotones folder and inside that theres another folder with those three sets or presets I just mentioned.)
To use sets of colors that are guaranteed to work together, click the dialogs Load button to get to Adobes Duotone Presets folder. Unless youre a graphics designer and familiar with Pantone colors the best way to find a combination is to click and try. Hint: The warm and cool tones are clearly identified so that will point you in the right direction. If you don’t like the results that you get from a particular preset, keep trying others until you find one that you like. To retain the subtle colors you just added, you’ll need to convert the Duotone file back into RGB format and save the finished file in Photoshops native format (.PSD) or another formats such as TIFF so you can make prints. If the image will just be used on the Web, fuggedaboudit and just use Photoshops Save for Web command.
Joe is the author of Creative Digital Monochrome Effects (http://amzn.to/echu3G) published by Lark Books.