Duotone is not a filter, it's a mode, and is used to print in an offset press a monochrome image with two or more inks, sometimes trying to simil a silver or platinum prints. The best photo books are printed in this method.
The reason I use this mode is to show in a computer screen how this image renders if it's printed in silver
Hehehe...there I am jumping to conclusions! Sorry, I thought you used a Duotone plug-in to PS to create the image. Still would be interested to see it without the duotone.