I was asked the other day to provide a "decent way to convert color [images] to duotone and still retain relevant information". I learned later that they wanted quite a bit more than this, but I proceeded to create the instructions to do so.

While these images may not portray the issue very well, this method does give the user total control over the gradation of converting the image to a grayscale image, preparing for a duotone conversion. Figure one is the original image, Figure two was the sample that the author wanted more control over, and figure 3 is the controlled conversion.

For the full tutorial visit: http://frederickweb.com/duotone-demo/color2duo4don.htm